xref: /openbmc/u-boot/README (revision ba7cc6c6)
1#
2# (C) Copyright 2000 - 2013
3# Wolfgang Denk, DENX Software Engineering, wd@denx.de.
4#
5# SPDX-License-Identifier:	GPL-2.0+
6#
7
8Summary:
9========
10
11This directory contains the source code for U-Boot, a boot loader for
12Embedded boards based on PowerPC, ARM, MIPS and several other
13processors, which can be installed in a boot ROM and used to
14initialize and test the hardware or to download and run application
15code.
16
17The development of U-Boot is closely related to Linux: some parts of
18the source code originate in the Linux source tree, we have some
19header files in common, and special provision has been made to
20support booting of Linux images.
21
22Some attention has been paid to make this software easily
23configurable and extendable. For instance, all monitor commands are
24implemented with the same call interface, so that it's very easy to
25add new commands. Also, instead of permanently adding rarely used
26code (for instance hardware test utilities) to the monitor, you can
27load and run it dynamically.
28
29
30Status:
31=======
32
33In general, all boards for which a configuration option exists in the
34Makefile have been tested to some extent and can be considered
35"working". In fact, many of them are used in production systems.
36
37In case of problems see the CHANGELOG file to find out who contributed
38the specific port. In addition, there are various MAINTAINERS files
39scattered throughout the U-Boot source identifying the people or
40companies responsible for various boards and subsystems.
41
42Note: As of August, 2010, there is no longer a CHANGELOG file in the
43actual U-Boot source tree; however, it can be created dynamically
44from the Git log using:
45
46	make CHANGELOG
47
48
49Where to get help:
50==================
51
52In case you have questions about, problems with or contributions for
53U-Boot, you should send a message to the U-Boot mailing list at
54<u-boot@lists.denx.de>. There is also an archive of previous traffic
55on the mailing list - please search the archive before asking FAQ's.
56Please see http://lists.denx.de/pipermail/u-boot and
57http://dir.gmane.org/gmane.comp.boot-loaders.u-boot
58
59
60Where to get source code:
61=========================
62
63The U-Boot source code is maintained in the Git repository at
64git://www.denx.de/git/u-boot.git ; you can browse it online at
65http://www.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=summary
66
67The "snapshot" links on this page allow you to download tarballs of
68any version you might be interested in. Official releases are also
69available for FTP download from the ftp://ftp.denx.de/pub/u-boot/
70directory.
71
72Pre-built (and tested) images are available from
73ftp://ftp.denx.de/pub/u-boot/images/
74
75
76Where we come from:
77===================
78
79- start from 8xxrom sources
80- create PPCBoot project (http://sourceforge.net/projects/ppcboot)
81- clean up code
82- make it easier to add custom boards
83- make it possible to add other [PowerPC] CPUs
84- extend functions, especially:
85  * Provide extended interface to Linux boot loader
86  * S-Record download
87  * network boot
88  * PCMCIA / CompactFlash / ATA disk / SCSI ... boot
89- create ARMBoot project (http://sourceforge.net/projects/armboot)
90- add other CPU families (starting with ARM)
91- create U-Boot project (http://sourceforge.net/projects/u-boot)
92- current project page: see http://www.denx.de/wiki/U-Boot
93
94
95Names and Spelling:
96===================
97
98The "official" name of this project is "Das U-Boot". The spelling
99"U-Boot" shall be used in all written text (documentation, comments
100in source files etc.). Example:
101
102	This is the README file for the U-Boot project.
103
104File names etc. shall be based on the string "u-boot". Examples:
105
106	include/asm-ppc/u-boot.h
107
108	#include <asm/u-boot.h>
109
110Variable names, preprocessor constants etc. shall be either based on
111the string "u_boot" or on "U_BOOT". Example:
112
113	U_BOOT_VERSION		u_boot_logo
114	IH_OS_U_BOOT		u_boot_hush_start
115
116
117Versioning:
118===========
119
120Starting with the release in October 2008, the names of the releases
121were changed from numerical release numbers without deeper meaning
122into a time stamp based numbering. Regular releases are identified by
123names consisting of the calendar year and month of the release date.
124Additional fields (if present) indicate release candidates or bug fix
125releases in "stable" maintenance trees.
126
127Examples:
128	U-Boot v2009.11	    - Release November 2009
129	U-Boot v2009.11.1   - Release 1 in version November 2009 stable tree
130	U-Boot v2010.09-rc1 - Release candidate 1 for September 2010 release
131
132
133Directory Hierarchy:
134====================
135
136/arch			Architecture specific files
137  /arc			Files generic to ARC architecture
138  /arm			Files generic to ARM architecture
139  /m68k			Files generic to m68k architecture
140  /microblaze		Files generic to microblaze architecture
141  /mips			Files generic to MIPS architecture
142  /nds32		Files generic to NDS32 architecture
143  /nios2		Files generic to Altera NIOS2 architecture
144  /openrisc		Files generic to OpenRISC architecture
145  /powerpc		Files generic to PowerPC architecture
146  /sandbox		Files generic to HW-independent "sandbox"
147  /sh			Files generic to SH architecture
148  /x86			Files generic to x86 architecture
149/api			Machine/arch independent API for external apps
150/board			Board dependent files
151/cmd			U-Boot commands functions
152/common			Misc architecture independent functions
153/configs		Board default configuration files
154/disk			Code for disk drive partition handling
155/doc			Documentation (don't expect too much)
156/drivers		Commonly used device drivers
157/dts			Contains Makefile for building internal U-Boot fdt.
158/examples		Example code for standalone applications, etc.
159/fs			Filesystem code (cramfs, ext2, jffs2, etc.)
160/include		Header Files
161/lib			Library routines generic to all architectures
162/Licenses		Various license files
163/net			Networking code
164/post			Power On Self Test
165/scripts		Various build scripts and Makefiles
166/test			Various unit test files
167/tools			Tools to build S-Record or U-Boot images, etc.
168
169Software Configuration:
170=======================
171
172Configuration is usually done using C preprocessor defines; the
173rationale behind that is to avoid dead code whenever possible.
174
175There are two classes of configuration variables:
176
177* Configuration _OPTIONS_:
178  These are selectable by the user and have names beginning with
179  "CONFIG_".
180
181* Configuration _SETTINGS_:
182  These depend on the hardware etc. and should not be meddled with if
183  you don't know what you're doing; they have names beginning with
184  "CONFIG_SYS_".
185
186Previously, all configuration was done by hand, which involved creating
187symbolic links and editing configuration files manually. More recently,
188U-Boot has added the Kbuild infrastructure used by the Linux kernel,
189allowing you to use the "make menuconfig" command to configure your
190build.
191
192
193Selection of Processor Architecture and Board Type:
194---------------------------------------------------
195
196For all supported boards there are ready-to-use default
197configurations available; just type "make <board_name>_defconfig".
198
199Example: For a TQM823L module type:
200
201	cd u-boot
202	make TQM823L_defconfig
203
204Note: If you're looking for the default configuration file for a board
205you're sure used to be there but is now missing, check the file
206doc/README.scrapyard for a list of no longer supported boards.
207
208Sandbox Environment:
209--------------------
210
211U-Boot can be built natively to run on a Linux host using the 'sandbox'
212board. This allows feature development which is not board- or architecture-
213specific to be undertaken on a native platform. The sandbox is also used to
214run some of U-Boot's tests.
215
216See board/sandbox/README.sandbox for more details.
217
218
219Board Initialisation Flow:
220--------------------------
221
222This is the intended start-up flow for boards. This should apply for both
223SPL and U-Boot proper (i.e. they both follow the same rules).
224
225Note: "SPL" stands for "Secondary Program Loader," which is explained in
226more detail later in this file.
227
228At present, SPL mostly uses a separate code path, but the function names
229and roles of each function are the same. Some boards or architectures
230may not conform to this.  At least most ARM boards which use
231CONFIG_SPL_FRAMEWORK conform to this.
232
233Execution typically starts with an architecture-specific (and possibly
234CPU-specific) start.S file, such as:
235
236	- arch/arm/cpu/armv7/start.S
237	- arch/powerpc/cpu/mpc83xx/start.S
238	- arch/mips/cpu/start.S
239
240and so on. From there, three functions are called; the purpose and
241limitations of each of these functions are described below.
242
243lowlevel_init():
244	- purpose: essential init to permit execution to reach board_init_f()
245	- no global_data or BSS
246	- there is no stack (ARMv7 may have one but it will soon be removed)
247	- must not set up SDRAM or use console
248	- must only do the bare minimum to allow execution to continue to
249		board_init_f()
250	- this is almost never needed
251	- return normally from this function
252
253board_init_f():
254	- purpose: set up the machine ready for running board_init_r():
255		i.e. SDRAM and serial UART
256	- global_data is available
257	- stack is in SRAM
258	- BSS is not available, so you cannot use global/static variables,
259		only stack variables and global_data
260
261	Non-SPL-specific notes:
262	- dram_init() is called to set up DRAM. If already done in SPL this
263		can do nothing
264
265	SPL-specific notes:
266	- you can override the entire board_init_f() function with your own
267		version as needed.
268	- preloader_console_init() can be called here in extremis
269	- should set up SDRAM, and anything needed to make the UART work
270	- these is no need to clear BSS, it will be done by crt0.S
271	- must return normally from this function (don't call board_init_r()
272		directly)
273
274Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at
275this point the stack and global_data are relocated to below
276CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of
277memory.
278
279board_init_r():
280	- purpose: main execution, common code
281	- global_data is available
282	- SDRAM is available
283	- BSS is available, all static/global variables can be used
284	- execution eventually continues to main_loop()
285
286	Non-SPL-specific notes:
287	- U-Boot is relocated to the top of memory and is now running from
288		there.
289
290	SPL-specific notes:
291	- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
292		CONFIG_SPL_STACK_R_ADDR points into SDRAM
293	- preloader_console_init() can be called here - typically this is
294		done by selecting CONFIG_SPL_BOARD_INIT and then supplying a
295		spl_board_init() function containing this call
296	- loads U-Boot or (in falcon mode) Linux
297
298
299
300Configuration Options:
301----------------------
302
303Configuration depends on the combination of board and CPU type; all
304such information is kept in a configuration file
305"include/configs/<board_name>.h".
306
307Example: For a TQM823L module, all configuration settings are in
308"include/configs/TQM823L.h".
309
310
311Many of the options are named exactly as the corresponding Linux
312kernel configuration options. The intention is to make it easier to
313build a config tool - later.
314
315
316The following options need to be configured:
317
318- CPU Type:	Define exactly one, e.g. CONFIG_MPC85XX.
319
320- Board Type:	Define exactly one, e.g. CONFIG_MPC8540ADS.
321
322- Marvell Family Member
323		CONFIG_SYS_MVFS		- define it if you want to enable
324					  multiple fs option at one time
325					  for marvell soc family
326
327- 85xx CPU Options:
328		CONFIG_SYS_PPC64
329
330		Specifies that the core is a 64-bit PowerPC implementation (implements
331		the "64" category of the Power ISA). This is necessary for ePAPR
332		compliance, among other possible reasons.
333
334		CONFIG_SYS_FSL_TBCLK_DIV
335
336		Defines the core time base clock divider ratio compared to the
337		system clock.  On most PQ3 devices this is 8, on newer QorIQ
338		devices it can be 16 or 32.  The ratio varies from SoC to Soc.
339
340		CONFIG_SYS_FSL_PCIE_COMPAT
341
342		Defines the string to utilize when trying to match PCIe device
343		tree nodes for the given platform.
344
345		CONFIG_SYS_FSL_ERRATUM_A004510
346
347		Enables a workaround for erratum A004510.  If set,
348		then CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV and
349		CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY must be set.
350
351		CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV
352		CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV2 (optional)
353
354		Defines one or two SoC revisions (low 8 bits of SVR)
355		for which the A004510 workaround should be applied.
356
357		The rest of SVR is either not relevant to the decision
358		of whether the erratum is present (e.g. p2040 versus
359		p2041) or is implied by the build target, which controls
360		whether CONFIG_SYS_FSL_ERRATUM_A004510 is set.
361
362		See Freescale App Note 4493 for more information about
363		this erratum.
364
365		CONFIG_A003399_NOR_WORKAROUND
366		Enables a workaround for IFC erratum A003399. It is only
367		required during NOR boot.
368
369		CONFIG_A008044_WORKAROUND
370		Enables a workaround for T1040/T1042 erratum A008044. It is only
371		required during NAND boot and valid for Rev 1.0 SoC revision
372
373		CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY
374
375		This is the value to write into CCSR offset 0x18600
376		according to the A004510 workaround.
377
378		CONFIG_SYS_FSL_DSP_DDR_ADDR
379		This value denotes start offset of DDR memory which is
380		connected exclusively to the DSP cores.
381
382		CONFIG_SYS_FSL_DSP_M2_RAM_ADDR
383		This value denotes start offset of M2 memory
384		which is directly connected to the DSP core.
385
386		CONFIG_SYS_FSL_DSP_M3_RAM_ADDR
387		This value denotes start offset of M3 memory which is directly
388		connected to the DSP core.
389
390		CONFIG_SYS_FSL_DSP_CCSRBAR_DEFAULT
391		This value denotes start offset of DSP CCSR space.
392
393		CONFIG_SYS_FSL_SINGLE_SOURCE_CLK
394		Single Source Clock is clocking mode present in some of FSL SoC's.
395		In this mode, a single differential clock is used to supply
396		clocks to the sysclock, ddrclock and usbclock.
397
398		CONFIG_SYS_CPC_REINIT_F
399		This CONFIG is defined when the CPC is configured as SRAM at the
400		time of U-Boot entry and is required to be re-initialized.
401
402		CONFIG_DEEP_SLEEP
403		Indicates this SoC supports deep sleep feature. If deep sleep is
404		supported, core will start to execute uboot when wakes up.
405
406- Generic CPU options:
407		CONFIG_SYS_GENERIC_GLOBAL_DATA
408		Defines global data is initialized in generic board board_init_f().
409		If this macro is defined, global data is created and cleared in
410		generic board board_init_f(). Without this macro, architecture/board
411		should initialize global data before calling board_init_f().
412
413		CONFIG_SYS_BIG_ENDIAN, CONFIG_SYS_LITTLE_ENDIAN
414
415		Defines the endianess of the CPU. Implementation of those
416		values is arch specific.
417
418		CONFIG_SYS_FSL_DDR
419		Freescale DDR driver in use. This type of DDR controller is
420		found in mpc83xx, mpc85xx, mpc86xx as well as some ARM core
421		SoCs.
422
423		CONFIG_SYS_FSL_DDR_ADDR
424		Freescale DDR memory-mapped register base.
425
426		CONFIG_SYS_FSL_DDR_EMU
427		Specify emulator support for DDR. Some DDR features such as
428		deskew training are not available.
429
430		CONFIG_SYS_FSL_DDRC_GEN1
431		Freescale DDR1 controller.
432
433		CONFIG_SYS_FSL_DDRC_GEN2
434		Freescale DDR2 controller.
435
436		CONFIG_SYS_FSL_DDRC_GEN3
437		Freescale DDR3 controller.
438
439		CONFIG_SYS_FSL_DDRC_GEN4
440		Freescale DDR4 controller.
441
442		CONFIG_SYS_FSL_DDRC_ARM_GEN3
443		Freescale DDR3 controller for ARM-based SoCs.
444
445		CONFIG_SYS_FSL_DDR1
446		Board config to use DDR1. It can be enabled for SoCs with
447		Freescale DDR1 or DDR2 controllers, depending on the board
448		implemetation.
449
450		CONFIG_SYS_FSL_DDR2
451		Board config to use DDR2. It can be enabled for SoCs with
452		Freescale DDR2 or DDR3 controllers, depending on the board
453		implementation.
454
455		CONFIG_SYS_FSL_DDR3
456		Board config to use DDR3. It can be enabled for SoCs with
457		Freescale DDR3 or DDR3L controllers.
458
459		CONFIG_SYS_FSL_DDR3L
460		Board config to use DDR3L. It can be enabled for SoCs with
461		DDR3L controllers.
462
463		CONFIG_SYS_FSL_DDR4
464		Board config to use DDR4. It can be enabled for SoCs with
465		DDR4 controllers.
466
467		CONFIG_SYS_FSL_IFC_BE
468		Defines the IFC controller register space as Big Endian
469
470		CONFIG_SYS_FSL_IFC_LE
471		Defines the IFC controller register space as Little Endian
472
473		CONFIG_SYS_FSL_IFC_CLK_DIV
474		Defines divider of platform clock(clock input to IFC controller).
475
476		CONFIG_SYS_FSL_LBC_CLK_DIV
477		Defines divider of platform clock(clock input to eLBC controller).
478
479		CONFIG_SYS_FSL_PBL_PBI
480		It enables addition of RCW (Power on reset configuration) in built image.
481		Please refer doc/README.pblimage for more details
482
483		CONFIG_SYS_FSL_PBL_RCW
484		It adds PBI(pre-boot instructions) commands in u-boot build image.
485		PBI commands can be used to configure SoC before it starts the execution.
486		Please refer doc/README.pblimage for more details
487
488		CONFIG_SPL_FSL_PBL
489		It adds a target to create boot binary having SPL binary in PBI format
490		concatenated with u-boot binary.
491
492		CONFIG_SYS_FSL_DDR_BE
493		Defines the DDR controller register space as Big Endian
494
495		CONFIG_SYS_FSL_DDR_LE
496		Defines the DDR controller register space as Little Endian
497
498		CONFIG_SYS_FSL_DDR_SDRAM_BASE_PHY
499		Physical address from the view of DDR controllers. It is the
500		same as CONFIG_SYS_DDR_SDRAM_BASE for  all Power SoCs. But
501		it could be different for ARM SoCs.
502
503		CONFIG_SYS_FSL_DDR_INTLV_256B
504		DDR controller interleaving on 256-byte. This is a special
505		interleaving mode, handled by Dickens for Freescale layerscape
506		SoCs with ARM core.
507
508		CONFIG_SYS_FSL_DDR_MAIN_NUM_CTRLS
509		Number of controllers used as main memory.
510
511		CONFIG_SYS_FSL_OTHER_DDR_NUM_CTRLS
512		Number of controllers used for other than main memory.
513
514		CONFIG_SYS_FSL_HAS_DP_DDR
515		Defines the SoC has DP-DDR used for DPAA.
516
517		CONFIG_SYS_FSL_SEC_BE
518		Defines the SEC controller register space as Big Endian
519
520		CONFIG_SYS_FSL_SEC_LE
521		Defines the SEC controller register space as Little Endian
522
523- MIPS CPU options:
524		CONFIG_SYS_INIT_SP_OFFSET
525
526		Offset relative to CONFIG_SYS_SDRAM_BASE for initial stack
527		pointer. This is needed for the temporary stack before
528		relocation.
529
530		CONFIG_SYS_MIPS_CACHE_MODE
531
532		Cache operation mode for the MIPS CPU.
533		See also arch/mips/include/asm/mipsregs.h.
534		Possible values are:
535			CONF_CM_CACHABLE_NO_WA
536			CONF_CM_CACHABLE_WA
537			CONF_CM_UNCACHED
538			CONF_CM_CACHABLE_NONCOHERENT
539			CONF_CM_CACHABLE_CE
540			CONF_CM_CACHABLE_COW
541			CONF_CM_CACHABLE_CUW
542			CONF_CM_CACHABLE_ACCELERATED
543
544		CONFIG_SYS_XWAY_EBU_BOOTCFG
545
546		Special option for Lantiq XWAY SoCs for booting from NOR flash.
547		See also arch/mips/cpu/mips32/start.S.
548
549		CONFIG_XWAY_SWAP_BYTES
550
551		Enable compilation of tools/xway-swap-bytes needed for Lantiq
552		XWAY SoCs for booting from NOR flash. The U-Boot image needs to
553		be swapped if a flash programmer is used.
554
555- ARM options:
556		CONFIG_SYS_EXCEPTION_VECTORS_HIGH
557
558		Select high exception vectors of the ARM core, e.g., do not
559		clear the V bit of the c1 register of CP15.
560
561		COUNTER_FREQUENCY
562		Generic timer clock source frequency.
563
564		COUNTER_FREQUENCY_REAL
565		Generic timer clock source frequency if the real clock is
566		different from COUNTER_FREQUENCY, and can only be determined
567		at run time.
568
569- Tegra SoC options:
570		CONFIG_TEGRA_SUPPORT_NON_SECURE
571
572		Support executing U-Boot in non-secure (NS) mode. Certain
573		impossible actions will be skipped if the CPU is in NS mode,
574		such as ARM architectural timer initialization.
575
576- Linux Kernel Interface:
577		CONFIG_CLOCKS_IN_MHZ
578
579		U-Boot stores all clock information in Hz
580		internally. For binary compatibility with older Linux
581		kernels (which expect the clocks passed in the
582		bd_info data to be in MHz) the environment variable
583		"clocks_in_mhz" can be defined so that U-Boot
584		converts clock data to MHZ before passing it to the
585		Linux kernel.
586		When CONFIG_CLOCKS_IN_MHZ is defined, a definition of
587		"clocks_in_mhz=1" is automatically included in the
588		default environment.
589
590		CONFIG_MEMSIZE_IN_BYTES		[relevant for MIPS only]
591
592		When transferring memsize parameter to Linux, some versions
593		expect it to be in bytes, others in MB.
594		Define CONFIG_MEMSIZE_IN_BYTES to make it in bytes.
595
596		CONFIG_OF_LIBFDT
597
598		New kernel versions are expecting firmware settings to be
599		passed using flattened device trees (based on open firmware
600		concepts).
601
602		CONFIG_OF_LIBFDT
603		 * New libfdt-based support
604		 * Adds the "fdt" command
605		 * The bootm command automatically updates the fdt
606
607		OF_TBCLK - The timebase frequency.
608		OF_STDOUT_PATH - The path to the console device
609
610		boards with QUICC Engines require OF_QE to set UCC MAC
611		addresses
612
613		CONFIG_OF_BOARD_SETUP
614
615		Board code has addition modification that it wants to make
616		to the flat device tree before handing it off to the kernel
617
618		CONFIG_OF_SYSTEM_SETUP
619
620		Other code has addition modification that it wants to make
621		to the flat device tree before handing it off to the kernel.
622		This causes ft_system_setup() to be called before booting
623		the kernel.
624
625		CONFIG_OF_IDE_FIXUP
626
627		U-Boot can detect if an IDE device is present or not.
628		If not, and this new config option is activated, U-Boot
629		removes the ATA node from the DTS before booting Linux,
630		so the Linux IDE driver does not probe the device and
631		crash. This is needed for buggy hardware (uc101) where
632		no pull down resistor is connected to the signal IDE5V_DD7.
633
634		CONFIG_MACH_TYPE	[relevant for ARM only][mandatory]
635
636		This setting is mandatory for all boards that have only one
637		machine type and must be used to specify the machine type
638		number as it appears in the ARM machine registry
639		(see http://www.arm.linux.org.uk/developer/machines/).
640		Only boards that have multiple machine types supported
641		in a single configuration file and the machine type is
642		runtime discoverable, do not have to use this setting.
643
644- vxWorks boot parameters:
645
646		bootvx constructs a valid bootline using the following
647		environments variables: bootdev, bootfile, ipaddr, netmask,
648		serverip, gatewayip, hostname, othbootargs.
649		It loads the vxWorks image pointed bootfile.
650
651		Note: If a "bootargs" environment is defined, it will overwride
652		the defaults discussed just above.
653
654- Cache Configuration:
655		CONFIG_SYS_ICACHE_OFF - Do not enable instruction cache in U-Boot
656		CONFIG_SYS_DCACHE_OFF - Do not enable data cache in U-Boot
657		CONFIG_SYS_L2CACHE_OFF- Do not enable L2 cache in U-Boot
658
659- Cache Configuration for ARM:
660		CONFIG_SYS_L2_PL310 - Enable support for ARM PL310 L2 cache
661				      controller
662		CONFIG_SYS_PL310_BASE - Physical base address of PL310
663					controller register space
664
665- Serial Ports:
666		CONFIG_PL010_SERIAL
667
668		Define this if you want support for Amba PrimeCell PL010 UARTs.
669
670		CONFIG_PL011_SERIAL
671
672		Define this if you want support for Amba PrimeCell PL011 UARTs.
673
674		CONFIG_PL011_CLOCK
675
676		If you have Amba PrimeCell PL011 UARTs, set this variable to
677		the clock speed of the UARTs.
678
679		CONFIG_PL01x_PORTS
680
681		If you have Amba PrimeCell PL010 or PL011 UARTs on your board,
682		define this to a list of base addresses for each (supported)
683		port. See e.g. include/configs/versatile.h
684
685		CONFIG_SERIAL_HW_FLOW_CONTROL
686
687		Define this variable to enable hw flow control in serial driver.
688		Current user of this option is drivers/serial/nsl16550.c driver
689
690- Console Baudrate:
691		CONFIG_BAUDRATE - in bps
692		Select one of the baudrates listed in
693		CONFIG_SYS_BAUDRATE_TABLE, see below.
694
695- Autoboot Command:
696		CONFIG_BOOTCOMMAND
697		Only needed when CONFIG_BOOTDELAY is enabled;
698		define a command string that is automatically executed
699		when no character is read on the console interface
700		within "Boot Delay" after reset.
701
702		CONFIG_BOOTARGS
703		This can be used to pass arguments to the bootm
704		command. The value of CONFIG_BOOTARGS goes into the
705		environment value "bootargs".
706
707		CONFIG_RAMBOOT and CONFIG_NFSBOOT
708		The value of these goes into the environment as
709		"ramboot" and "nfsboot" respectively, and can be used
710		as a convenience, when switching between booting from
711		RAM and NFS.
712
713- Bootcount:
714		CONFIG_BOOTCOUNT_LIMIT
715		Implements a mechanism for detecting a repeating reboot
716		cycle, see:
717		http://www.denx.de/wiki/view/DULG/UBootBootCountLimit
718
719		CONFIG_BOOTCOUNT_ENV
720		If no softreset save registers are found on the hardware
721		"bootcount" is stored in the environment. To prevent a
722		saveenv on all reboots, the environment variable
723		"upgrade_available" is used. If "upgrade_available" is
724		0, "bootcount" is always 0, if "upgrade_available" is
725		1 "bootcount" is incremented in the environment.
726		So the Userspace Applikation must set the "upgrade_available"
727		and "bootcount" variable to 0, if a boot was successfully.
728
729- Pre-Boot Commands:
730		CONFIG_PREBOOT
731
732		When this option is #defined, the existence of the
733		environment variable "preboot" will be checked
734		immediately before starting the CONFIG_BOOTDELAY
735		countdown and/or running the auto-boot command resp.
736		entering interactive mode.
737
738		This feature is especially useful when "preboot" is
739		automatically generated or modified. For an example
740		see the LWMON board specific code: here "preboot" is
741		modified when the user holds down a certain
742		combination of keys on the (special) keyboard when
743		booting the systems
744
745- Serial Download Echo Mode:
746		CONFIG_LOADS_ECHO
747		If defined to 1, all characters received during a
748		serial download (using the "loads" command) are
749		echoed back. This might be needed by some terminal
750		emulations (like "cu"), but may as well just take
751		time on others. This setting #define's the initial
752		value of the "loads_echo" environment variable.
753
754- Kgdb Serial Baudrate: (if CONFIG_CMD_KGDB is defined)
755		CONFIG_KGDB_BAUDRATE
756		Select one of the baudrates listed in
757		CONFIG_SYS_BAUDRATE_TABLE, see below.
758
759- Monitor Functions:
760		Monitor commands can be included or excluded
761		from the build by using the #include files
762		<config_cmd_all.h> and #undef'ing unwanted
763		commands, or adding #define's for wanted commands.
764
765		The default command configuration includes all commands
766		except those marked below with a "*".
767
768		CONFIG_CMD_AES		  AES 128 CBC encrypt/decrypt
769		CONFIG_CMD_ASKENV	* ask for env variable
770		CONFIG_CMD_BDI		  bdinfo
771		CONFIG_CMD_BOOTD	  bootd
772		CONFIG_CMD_BOOTI	* ARM64 Linux kernel Image support
773		CONFIG_CMD_CACHE	* icache, dcache
774		CONFIG_CMD_CONSOLE	  coninfo
775		CONFIG_CMD_DHCP		* DHCP support
776		CONFIG_CMD_DIAG		* Diagnostics
777		CONFIG_CMD_ECHO		  echo arguments
778		CONFIG_CMD_EDITENV	  edit env variable
779		CONFIG_CMD_ELF		* bootelf, bootvx
780		CONFIG_CMD_ENV_EXISTS	* check existence of env variable
781		CONFIG_CMD_EXPORTENV	* export the environment
782		CONFIG_CMD_EXT2		* ext2 command support
783		CONFIG_CMD_EXT4		* ext4 command support
784		CONFIG_CMD_FS_GENERIC	* filesystem commands (e.g. load, ls)
785					  that work for multiple fs types
786		CONFIG_CMD_FS_UUID	* Look up a filesystem UUID
787		CONFIG_CMD_SAVEENV	  saveenv
788		CONFIG_CMD_FLASH	  flinfo, erase, protect
789		CONFIG_CMD_FPGA		  FPGA device initialization support
790		CONFIG_CMD_GO		* the 'go' command (exec code)
791		CONFIG_CMD_GREPENV	* search environment
792		CONFIG_CMD_I2C		* I2C serial bus support
793		CONFIG_CMD_IMI		  iminfo
794		CONFIG_CMD_IMLS		  List all images found in NOR flash
795		CONFIG_CMD_IMLS_NAND	* List all images found in NAND flash
796		CONFIG_CMD_IMPORTENV	* import an environment
797		CONFIG_CMD_INI		* import data from an ini file into the env
798		CONFIG_CMD_ITEST	  Integer/string test of 2 values
799		CONFIG_CMD_LDRINFO	* ldrinfo (display Blackfin loader)
800		CONFIG_CMD_LINK_LOCAL	* link-local IP address auto-configuration
801					  (169.254.*.*)
802		CONFIG_CMD_LOADB	  loadb
803		CONFIG_CMD_LOADS	  loads
804		CONFIG_CMD_MD5SUM	* print md5 message digest
805					  (requires CONFIG_CMD_MEMORY and CONFIG_MD5)
806		CONFIG_CMD_MEMINFO	* Display detailed memory information
807		CONFIG_CMD_MEMORY	  md, mm, nm, mw, cp, cmp, crc, base,
808					  loop, loopw
809		CONFIG_CMD_MEMTEST	* mtest
810		CONFIG_CMD_MISC		  Misc functions like sleep etc
811		CONFIG_CMD_MMC		* MMC memory mapped support
812		CONFIG_CMD_MII		* MII utility commands
813		CONFIG_CMD_NET		  bootp, tftpboot, rarpboot
814		CONFIG_CMD_NFS		  NFS support
815		CONFIG_CMD_PCI		* pciinfo
816		CONFIG_CMD_PCMCIA		* PCMCIA support
817		CONFIG_CMD_PING		* send ICMP ECHO_REQUEST to network
818					  host
819		CONFIG_CMD_PORTIO	* Port I/O
820		CONFIG_CMD_READ		* Read raw data from partition
821		CONFIG_CMD_REGINFO	* Register dump
822		CONFIG_CMD_RUN		  run command in env variable
823		CONFIG_CMD_SANDBOX	* sb command to access sandbox features
824		CONFIG_CMD_SAVES	* save S record dump
825		CONFIG_CMD_SDRAM	* print SDRAM configuration information
826					  (requires CONFIG_CMD_I2C)
827		CONFIG_CMD_SF		* Read/write/erase SPI NOR flash
828		CONFIG_CMD_SOFTSWITCH	* Soft switch setting command for BF60x
829		CONFIG_CMD_SOURCE	  "source" command Support
830		CONFIG_CMD_SPI		* SPI serial bus support
831		CONFIG_CMD_TFTPSRV	* TFTP transfer in server mode
832		CONFIG_CMD_TFTPPUT	* TFTP put command (upload)
833		CONFIG_CMD_TIME		* run command and report execution time (ARM specific)
834		CONFIG_CMD_TIMER	* access to the system tick timer
835		CONFIG_CMD_USB		* USB support
836		CONFIG_CMD_CDP		* Cisco Discover Protocol support
837		CONFIG_CMD_XIMG		  Load part of Multi Image
838		CONFIG_CMD_UUID		* Generate random UUID or GUID string
839
840		EXAMPLE: If you want all functions except of network
841		support you can write:
842
843		#include "config_cmd_all.h"
844		#undef CONFIG_CMD_NET
845
846	Other Commands:
847		fdt (flattened device tree) command: CONFIG_OF_LIBFDT
848
849	Note:	Don't enable the "icache" and "dcache" commands
850		(configuration option CONFIG_CMD_CACHE) unless you know
851		what you (and your U-Boot users) are doing. Data
852		cache cannot be enabled on systems like the
853		8xx (where accesses to the IMMR region must be
854		uncached), and it cannot be disabled on all other
855		systems where we (mis-) use the data cache to hold an
856		initial stack and some data.
857
858
859		XXX - this list needs to get updated!
860
861- Removal of commands
862		If no commands are needed to boot, you can disable
863		CONFIG_CMDLINE to remove them. In this case, the command line
864		will not be available, and when U-Boot wants to execute the
865		boot command (on start-up) it will call board_run_command()
866		instead. This can reduce image size significantly for very
867		simple boot procedures.
868
869- Regular expression support:
870		CONFIG_REGEX
871		If this variable is defined, U-Boot is linked against
872		the SLRE (Super Light Regular Expression) library,
873		which adds regex support to some commands, as for
874		example "env grep" and "setexpr".
875
876- Device tree:
877		CONFIG_OF_CONTROL
878		If this variable is defined, U-Boot will use a device tree
879		to configure its devices, instead of relying on statically
880		compiled #defines in the board file. This option is
881		experimental and only available on a few boards. The device
882		tree is available in the global data as gd->fdt_blob.
883
884		U-Boot needs to get its device tree from somewhere. This can
885		be done using one of the three options below:
886
887		CONFIG_OF_EMBED
888		If this variable is defined, U-Boot will embed a device tree
889		binary in its image. This device tree file should be in the
890		board directory and called <soc>-<board>.dts. The binary file
891		is then picked up in board_init_f() and made available through
892		the global data structure as gd->blob.
893
894		CONFIG_OF_SEPARATE
895		If this variable is defined, U-Boot will build a device tree
896		binary. It will be called u-boot.dtb. Architecture-specific
897		code will locate it at run-time. Generally this works by:
898
899			cat u-boot.bin u-boot.dtb >image.bin
900
901		and in fact, U-Boot does this for you, creating a file called
902		u-boot-dtb.bin which is useful in the common case. You can
903		still use the individual files if you need something more
904		exotic.
905
906		CONFIG_OF_BOARD
907		If this variable is defined, U-Boot will use the device tree
908		provided by the board at runtime instead of embedding one with
909		the image. Only boards defining board_fdt_blob_setup() support
910		this option (see include/fdtdec.h file).
911
912- Watchdog:
913		CONFIG_WATCHDOG
914		If this variable is defined, it enables watchdog
915		support for the SoC. There must be support in the SoC
916		specific code for a watchdog. For the 8xx
917		CPUs, the SIU Watchdog feature is enabled in the SYPCR
918		register.  When supported for a specific SoC is
919		available, then no further board specific code should
920		be needed to use it.
921
922		CONFIG_HW_WATCHDOG
923		When using a watchdog circuitry external to the used
924		SoC, then define this variable and provide board
925		specific code for the "hw_watchdog_reset" function.
926
927		CONFIG_AT91_HW_WDT_TIMEOUT
928		specify the timeout in seconds. default 2 seconds.
929
930- U-Boot Version:
931		CONFIG_VERSION_VARIABLE
932		If this variable is defined, an environment variable
933		named "ver" is created by U-Boot showing the U-Boot
934		version as printed by the "version" command.
935		Any change to this variable will be reverted at the
936		next reset.
937
938- Real-Time Clock:
939
940		When CONFIG_CMD_DATE is selected, the type of the RTC
941		has to be selected, too. Define exactly one of the
942		following options:
943
944		CONFIG_RTC_PCF8563	- use Philips PCF8563 RTC
945		CONFIG_RTC_MC13XXX	- use MC13783 or MC13892 RTC
946		CONFIG_RTC_MC146818	- use MC146818 RTC
947		CONFIG_RTC_DS1307	- use Maxim, Inc. DS1307 RTC
948		CONFIG_RTC_DS1337	- use Maxim, Inc. DS1337 RTC
949		CONFIG_RTC_DS1338	- use Maxim, Inc. DS1338 RTC
950		CONFIG_RTC_DS1339	- use Maxim, Inc. DS1339 RTC
951		CONFIG_RTC_DS164x	- use Dallas DS164x RTC
952		CONFIG_RTC_ISL1208	- use Intersil ISL1208 RTC
953		CONFIG_RTC_MAX6900	- use Maxim, Inc. MAX6900 RTC
954		CONFIG_RTC_DS1337_NOOSC	- Turn off the OSC output for DS1337
955		CONFIG_SYS_RV3029_TCR	- enable trickle charger on
956					  RV3029 RTC.
957
958		Note that if the RTC uses I2C, then the I2C interface
959		must also be configured. See I2C Support, below.
960
961- GPIO Support:
962		CONFIG_PCA953X		- use NXP's PCA953X series I2C GPIO
963
964		The CONFIG_SYS_I2C_PCA953X_WIDTH option specifies a list of
965		chip-ngpio pairs that tell the PCA953X driver the number of
966		pins supported by a particular chip.
967
968		Note that if the GPIO device uses I2C, then the I2C interface
969		must also be configured. See I2C Support, below.
970
971- I/O tracing:
972		When CONFIG_IO_TRACE is selected, U-Boot intercepts all I/O
973		accesses and can checksum them or write a list of them out
974		to memory. See the 'iotrace' command for details. This is
975		useful for testing device drivers since it can confirm that
976		the driver behaves the same way before and after a code
977		change. Currently this is supported on sandbox and arm. To
978		add support for your architecture, add '#include <iotrace.h>'
979		to the bottom of arch/<arch>/include/asm/io.h and test.
980
981		Example output from the 'iotrace stats' command is below.
982		Note that if the trace buffer is exhausted, the checksum will
983		still continue to operate.
984
985			iotrace is enabled
986			Start:  10000000	(buffer start address)
987			Size:   00010000	(buffer size)
988			Offset: 00000120	(current buffer offset)
989			Output: 10000120	(start + offset)
990			Count:  00000018	(number of trace records)
991			CRC32:  9526fb66	(CRC32 of all trace records)
992
993- Timestamp Support:
994
995		When CONFIG_TIMESTAMP is selected, the timestamp
996		(date and time) of an image is printed by image
997		commands like bootm or iminfo. This option is
998		automatically enabled when you select CONFIG_CMD_DATE .
999
1000- Partition Labels (disklabels) Supported:
1001		Zero or more of the following:
1002		CONFIG_MAC_PARTITION   Apple's MacOS partition table.
1003		CONFIG_ISO_PARTITION   ISO partition table, used on CDROM etc.
1004		CONFIG_EFI_PARTITION   GPT partition table, common when EFI is the
1005				       bootloader.  Note 2TB partition limit; see
1006				       disk/part_efi.c
1007		CONFIG_MTD_PARTITIONS  Memory Technology Device partition table.
1008
1009		If IDE or SCSI support is enabled (CONFIG_IDE or
1010		CONFIG_SCSI) you must configure support for at
1011		least one non-MTD partition type as well.
1012
1013- IDE Reset method:
1014		CONFIG_IDE_RESET_ROUTINE - this is defined in several
1015		board configurations files but used nowhere!
1016
1017		CONFIG_IDE_RESET - is this is defined, IDE Reset will
1018		be performed by calling the function
1019			ide_set_reset(int reset)
1020		which has to be defined in a board specific file
1021
1022- ATAPI Support:
1023		CONFIG_ATAPI
1024
1025		Set this to enable ATAPI support.
1026
1027- LBA48 Support
1028		CONFIG_LBA48
1029
1030		Set this to enable support for disks larger than 137GB
1031		Also look at CONFIG_SYS_64BIT_LBA.
1032		Whithout these , LBA48 support uses 32bit variables and will 'only'
1033		support disks up to 2.1TB.
1034
1035		CONFIG_SYS_64BIT_LBA:
1036			When enabled, makes the IDE subsystem use 64bit sector addresses.
1037			Default is 32bit.
1038
1039- SCSI Support:
1040		CONFIG_SYS_SCSI_MAX_LUN [8], CONFIG_SYS_SCSI_MAX_SCSI_ID [7] and
1041		CONFIG_SYS_SCSI_MAX_DEVICE [CONFIG_SYS_SCSI_MAX_SCSI_ID *
1042		CONFIG_SYS_SCSI_MAX_LUN] can be adjusted to define the
1043		maximum numbers of LUNs, SCSI ID's and target
1044		devices.
1045
1046		The environment variable 'scsidevs' is set to the number of
1047		SCSI devices found during the last scan.
1048
1049- NETWORK Support (PCI):
1050		CONFIG_E1000
1051		Support for Intel 8254x/8257x gigabit chips.
1052
1053		CONFIG_E1000_SPI
1054		Utility code for direct access to the SPI bus on Intel 8257x.
1055		This does not do anything useful unless you set at least one
1056		of CONFIG_CMD_E1000 or CONFIG_E1000_SPI_GENERIC.
1057
1058		CONFIG_E1000_SPI_GENERIC
1059		Allow generic access to the SPI bus on the Intel 8257x, for
1060		example with the "sspi" command.
1061
1062		CONFIG_CMD_E1000
1063		Management command for E1000 devices.  When used on devices
1064		with SPI support you can reprogram the EEPROM from U-Boot.
1065
1066		CONFIG_EEPRO100
1067		Support for Intel 82557/82559/82559ER chips.
1068		Optional CONFIG_EEPRO100_SROM_WRITE enables EEPROM
1069		write routine for first time initialisation.
1070
1071		CONFIG_TULIP
1072		Support for Digital 2114x chips.
1073		Optional CONFIG_TULIP_SELECT_MEDIA for board specific
1074		modem chip initialisation (KS8761/QS6611).
1075
1076		CONFIG_NATSEMI
1077		Support for National dp83815 chips.
1078
1079		CONFIG_NS8382X
1080		Support for National dp8382[01] gigabit chips.
1081
1082- NETWORK Support (other):
1083
1084		CONFIG_DRIVER_AT91EMAC
1085		Support for AT91RM9200 EMAC.
1086
1087			CONFIG_RMII
1088			Define this to use reduced MII inteface
1089
1090			CONFIG_DRIVER_AT91EMAC_QUIET
1091			If this defined, the driver is quiet.
1092			The driver doen't show link status messages.
1093
1094		CONFIG_CALXEDA_XGMAC
1095		Support for the Calxeda XGMAC device
1096
1097		CONFIG_LAN91C96
1098		Support for SMSC's LAN91C96 chips.
1099
1100			CONFIG_LAN91C96_USE_32_BIT
1101			Define this to enable 32 bit addressing
1102
1103		CONFIG_SMC91111
1104		Support for SMSC's LAN91C111 chip
1105
1106			CONFIG_SMC91111_BASE
1107			Define this to hold the physical address
1108			of the device (I/O space)
1109
1110			CONFIG_SMC_USE_32_BIT
1111			Define this if data bus is 32 bits
1112
1113			CONFIG_SMC_USE_IOFUNCS
1114			Define this to use i/o functions instead of macros
1115			(some hardware wont work with macros)
1116
1117		CONFIG_DRIVER_TI_EMAC
1118		Support for davinci emac
1119
1120			CONFIG_SYS_DAVINCI_EMAC_PHY_COUNT
1121			Define this if you have more then 3 PHYs.
1122
1123		CONFIG_FTGMAC100
1124		Support for Faraday's FTGMAC100 Gigabit SoC Ethernet
1125
1126			CONFIG_FTGMAC100_EGIGA
1127			Define this to use GE link update with gigabit PHY.
1128			Define this if FTGMAC100 is connected to gigabit PHY.
1129			If your system has 10/100 PHY only, it might not occur
1130			wrong behavior. Because PHY usually return timeout or
1131			useless data when polling gigabit status and gigabit
1132			control registers. This behavior won't affect the
1133			correctnessof 10/100 link speed update.
1134
1135		CONFIG_SMC911X
1136		Support for SMSC's LAN911x and LAN921x chips
1137
1138			CONFIG_SMC911X_BASE
1139			Define this to hold the physical address
1140			of the device (I/O space)
1141
1142			CONFIG_SMC911X_32_BIT
1143			Define this if data bus is 32 bits
1144
1145			CONFIG_SMC911X_16_BIT
1146			Define this if data bus is 16 bits. If your processor
1147			automatically converts one 32 bit word to two 16 bit
1148			words you may also try CONFIG_SMC911X_32_BIT.
1149
1150		CONFIG_SH_ETHER
1151		Support for Renesas on-chip Ethernet controller
1152
1153			CONFIG_SH_ETHER_USE_PORT
1154			Define the number of ports to be used
1155
1156			CONFIG_SH_ETHER_PHY_ADDR
1157			Define the ETH PHY's address
1158
1159			CONFIG_SH_ETHER_CACHE_WRITEBACK
1160			If this option is set, the driver enables cache flush.
1161
1162- PWM Support:
1163		CONFIG_PWM_IMX
1164		Support for PWM module on the imx6.
1165
1166- TPM Support:
1167		CONFIG_TPM
1168		Support TPM devices.
1169
1170		CONFIG_TPM_TIS_INFINEON
1171		Support for Infineon i2c bus TPM devices. Only one device
1172		per system is supported at this time.
1173
1174			CONFIG_TPM_TIS_I2C_BURST_LIMITATION
1175			Define the burst count bytes upper limit
1176
1177		CONFIG_TPM_ST33ZP24
1178		Support for STMicroelectronics TPM devices. Requires DM_TPM support.
1179
1180			CONFIG_TPM_ST33ZP24_I2C
1181			Support for STMicroelectronics ST33ZP24 I2C devices.
1182			Requires TPM_ST33ZP24 and I2C.
1183
1184			CONFIG_TPM_ST33ZP24_SPI
1185			Support for STMicroelectronics ST33ZP24 SPI devices.
1186			Requires TPM_ST33ZP24 and SPI.
1187
1188		CONFIG_TPM_ATMEL_TWI
1189		Support for Atmel TWI TPM device. Requires I2C support.
1190
1191		CONFIG_TPM_TIS_LPC
1192		Support for generic parallel port TPM devices. Only one device
1193		per system is supported at this time.
1194
1195			CONFIG_TPM_TIS_BASE_ADDRESS
1196			Base address where the generic TPM device is mapped
1197			to. Contemporary x86 systems usually map it at
1198			0xfed40000.
1199
1200		CONFIG_CMD_TPM
1201		Add tpm monitor functions.
1202		Requires CONFIG_TPM. If CONFIG_TPM_AUTH_SESSIONS is set, also
1203		provides monitor access to authorized functions.
1204
1205		CONFIG_TPM
1206		Define this to enable the TPM support library which provides
1207		functional interfaces to some TPM commands.
1208		Requires support for a TPM device.
1209
1210		CONFIG_TPM_AUTH_SESSIONS
1211		Define this to enable authorized functions in the TPM library.
1212		Requires CONFIG_TPM and CONFIG_SHA1.
1213
1214- USB Support:
1215		At the moment only the UHCI host controller is
1216		supported (PIP405, MIP405); define
1217		CONFIG_USB_UHCI to enable it.
1218		define CONFIG_USB_KEYBOARD to enable the USB Keyboard
1219		and define CONFIG_USB_STORAGE to enable the USB
1220		storage devices.
1221		Note:
1222		Supported are USB Keyboards and USB Floppy drives
1223		(TEAC FD-05PUB).
1224
1225		CONFIG_USB_EHCI_TXFIFO_THRESH enables setting of the
1226		txfilltuning field in the EHCI controller on reset.
1227
1228		CONFIG_USB_DWC2_REG_ADDR the physical CPU address of the DWC2
1229		HW module registers.
1230
1231- USB Device:
1232		Define the below if you wish to use the USB console.
1233		Once firmware is rebuilt from a serial console issue the
1234		command "setenv stdin usbtty; setenv stdout usbtty" and
1235		attach your USB cable. The Unix command "dmesg" should print
1236		it has found a new device. The environment variable usbtty
1237		can be set to gserial or cdc_acm to enable your device to
1238		appear to a USB host as a Linux gserial device or a
1239		Common Device Class Abstract Control Model serial device.
1240		If you select usbtty = gserial you should be able to enumerate
1241		a Linux host by
1242		# modprobe usbserial vendor=0xVendorID product=0xProductID
1243		else if using cdc_acm, simply setting the environment
1244		variable usbtty to be cdc_acm should suffice. The following
1245		might be defined in YourBoardName.h
1246
1247			CONFIG_USB_DEVICE
1248			Define this to build a UDC device
1249
1250			CONFIG_USB_TTY
1251			Define this to have a tty type of device available to
1252			talk to the UDC device
1253
1254			CONFIG_USBD_HS
1255			Define this to enable the high speed support for usb
1256			device and usbtty. If this feature is enabled, a routine
1257			int is_usbd_high_speed(void)
1258			also needs to be defined by the driver to dynamically poll
1259			whether the enumeration has succeded at high speed or full
1260			speed.
1261
1262			CONFIG_SYS_CONSOLE_IS_IN_ENV
1263			Define this if you want stdin, stdout &/or stderr to
1264			be set to usbtty.
1265
1266		If you have a USB-IF assigned VendorID then you may wish to
1267		define your own vendor specific values either in BoardName.h
1268		or directly in usbd_vendor_info.h. If you don't define
1269		CONFIG_USBD_MANUFACTURER, CONFIG_USBD_PRODUCT_NAME,
1270		CONFIG_USBD_VENDORID and CONFIG_USBD_PRODUCTID, then U-Boot
1271		should pretend to be a Linux device to it's target host.
1272
1273			CONFIG_USBD_MANUFACTURER
1274			Define this string as the name of your company for
1275			- CONFIG_USBD_MANUFACTURER "my company"
1276
1277			CONFIG_USBD_PRODUCT_NAME
1278			Define this string as the name of your product
1279			- CONFIG_USBD_PRODUCT_NAME "acme usb device"
1280
1281			CONFIG_USBD_VENDORID
1282			Define this as your assigned Vendor ID from the USB
1283			Implementors Forum. This *must* be a genuine Vendor ID
1284			to avoid polluting the USB namespace.
1285			- CONFIG_USBD_VENDORID 0xFFFF
1286
1287			CONFIG_USBD_PRODUCTID
1288			Define this as the unique Product ID
1289			for your device
1290			- CONFIG_USBD_PRODUCTID 0xFFFF
1291
1292- ULPI Layer Support:
1293		The ULPI (UTMI Low Pin (count) Interface) PHYs are supported via
1294		the generic ULPI layer. The generic layer accesses the ULPI PHY
1295		via the platform viewport, so you need both the genric layer and
1296		the viewport enabled. Currently only Chipidea/ARC based
1297		viewport is supported.
1298		To enable the ULPI layer support, define CONFIG_USB_ULPI and
1299		CONFIG_USB_ULPI_VIEWPORT in your board configuration file.
1300		If your ULPI phy needs a different reference clock than the
1301		standard 24 MHz then you have to define CONFIG_ULPI_REF_CLK to
1302		the appropriate value in Hz.
1303
1304- MMC Support:
1305		The MMC controller on the Intel PXA is supported. To
1306		enable this define CONFIG_MMC. The MMC can be
1307		accessed from the boot prompt by mapping the device
1308		to physical memory similar to flash. Command line is
1309		enabled with CONFIG_CMD_MMC. The MMC driver also works with
1310		the FAT fs. This is enabled with CONFIG_CMD_FAT.
1311
1312		CONFIG_SH_MMCIF
1313		Support for Renesas on-chip MMCIF controller
1314
1315			CONFIG_SH_MMCIF_ADDR
1316			Define the base address of MMCIF registers
1317
1318			CONFIG_SH_MMCIF_CLK
1319			Define the clock frequency for MMCIF
1320
1321		CONFIG_SUPPORT_EMMC_BOOT
1322		Enable some additional features of the eMMC boot partitions.
1323
1324		CONFIG_SUPPORT_EMMC_RPMB
1325		Enable the commands for reading, writing and programming the
1326		key for the Replay Protection Memory Block partition in eMMC.
1327
1328- USB Device Firmware Update (DFU) class support:
1329		CONFIG_USB_FUNCTION_DFU
1330		This enables the USB portion of the DFU USB class
1331
1332		CONFIG_CMD_DFU
1333		This enables the command "dfu" which is used to have
1334		U-Boot create a DFU class device via USB.  This command
1335		requires that the "dfu_alt_info" environment variable be
1336		set and define the alt settings to expose to the host.
1337
1338		CONFIG_DFU_MMC
1339		This enables support for exposing (e)MMC devices via DFU.
1340
1341		CONFIG_DFU_NAND
1342		This enables support for exposing NAND devices via DFU.
1343
1344		CONFIG_DFU_RAM
1345		This enables support for exposing RAM via DFU.
1346		Note: DFU spec refer to non-volatile memory usage, but
1347		allow usages beyond the scope of spec - here RAM usage,
1348		one that would help mostly the developer.
1349
1350		CONFIG_SYS_DFU_DATA_BUF_SIZE
1351		Dfu transfer uses a buffer before writing data to the
1352		raw storage device. Make the size (in bytes) of this buffer
1353		configurable. The size of this buffer is also configurable
1354		through the "dfu_bufsiz" environment variable.
1355
1356		CONFIG_SYS_DFU_MAX_FILE_SIZE
1357		When updating files rather than the raw storage device,
1358		we use a static buffer to copy the file into and then write
1359		the buffer once we've been given the whole file.  Define
1360		this to the maximum filesize (in bytes) for the buffer.
1361		Default is 4 MiB if undefined.
1362
1363		DFU_DEFAULT_POLL_TIMEOUT
1364		Poll timeout [ms], is the timeout a device can send to the
1365		host. The host must wait for this timeout before sending
1366		a subsequent DFU_GET_STATUS request to the device.
1367
1368		DFU_MANIFEST_POLL_TIMEOUT
1369		Poll timeout [ms], which the device sends to the host when
1370		entering dfuMANIFEST state. Host waits this timeout, before
1371		sending again an USB request to the device.
1372
1373- USB Device Android Fastboot support:
1374		CONFIG_USB_FUNCTION_FASTBOOT
1375		This enables the USB part of the fastboot gadget
1376
1377		CONFIG_CMD_FASTBOOT
1378		This enables the command "fastboot" which enables the Android
1379		fastboot mode for the platform's USB device. Fastboot is a USB
1380		protocol for downloading images, flashing and device control
1381		used on Android devices.
1382		See doc/README.android-fastboot for more information.
1383
1384		CONFIG_ANDROID_BOOT_IMAGE
1385		This enables support for booting images which use the Android
1386		image format header.
1387
1388		CONFIG_FASTBOOT_BUF_ADDR
1389		The fastboot protocol requires a large memory buffer for
1390		downloads. Define this to the starting RAM address to use for
1391		downloaded images.
1392
1393		CONFIG_FASTBOOT_BUF_SIZE
1394		The fastboot protocol requires a large memory buffer for
1395		downloads. This buffer should be as large as possible for a
1396		platform. Define this to the size available RAM for fastboot.
1397
1398		CONFIG_FASTBOOT_FLASH
1399		The fastboot protocol includes a "flash" command for writing
1400		the downloaded image to a non-volatile storage device. Define
1401		this to enable the "fastboot flash" command.
1402
1403		CONFIG_FASTBOOT_FLASH_MMC_DEV
1404		The fastboot "flash" command requires additional information
1405		regarding the non-volatile storage device. Define this to
1406		the eMMC device that fastboot should use to store the image.
1407
1408		CONFIG_FASTBOOT_GPT_NAME
1409		The fastboot "flash" command supports writing the downloaded
1410		image to the Protective MBR and the Primary GUID Partition
1411		Table. (Additionally, this downloaded image is post-processed
1412		to generate and write the Backup GUID Partition Table.)
1413		This occurs when the specified "partition name" on the
1414		"fastboot flash" command line matches this value.
1415		The default is "gpt" if undefined.
1416
1417		CONFIG_FASTBOOT_MBR_NAME
1418		The fastboot "flash" command supports writing the downloaded
1419		image to DOS MBR.
1420		This occurs when the "partition name" specified on the
1421		"fastboot flash" command line matches this value.
1422		If not defined the default value "mbr" is used.
1423
1424- Journaling Flash filesystem support:
1425		CONFIG_JFFS2_NAND
1426		Define these for a default partition on a NAND device
1427
1428		CONFIG_SYS_JFFS2_FIRST_SECTOR,
1429		CONFIG_SYS_JFFS2_FIRST_BANK, CONFIG_SYS_JFFS2_NUM_BANKS
1430		Define these for a default partition on a NOR device
1431
1432- Keyboard Support:
1433		See Kconfig help for available keyboard drivers.
1434
1435		CONFIG_KEYBOARD
1436
1437		Define this to enable a custom keyboard support.
1438		This simply calls drv_keyboard_init() which must be
1439		defined in your board-specific files. This option is deprecated
1440		and is only used by novena. For new boards, use driver model
1441		instead.
1442
1443- Video support:
1444		CONFIG_FSL_DIU_FB
1445		Enable the Freescale DIU video driver.	Reference boards for
1446		SOCs that have a DIU should define this macro to enable DIU
1447		support, and should also define these other macros:
1448
1449			CONFIG_SYS_DIU_ADDR
1450			CONFIG_VIDEO
1451			CONFIG_CFB_CONSOLE
1452			CONFIG_VIDEO_SW_CURSOR
1453			CONFIG_VGA_AS_SINGLE_DEVICE
1454			CONFIG_VIDEO_LOGO
1455			CONFIG_VIDEO_BMP_LOGO
1456
1457		The DIU driver will look for the 'video-mode' environment
1458		variable, and if defined, enable the DIU as a console during
1459		boot.  See the documentation file doc/README.video for a
1460		description of this variable.
1461
1462- LCD Support:	CONFIG_LCD
1463
1464		Define this to enable LCD support (for output to LCD
1465		display); also select one of the supported displays
1466		by defining one of these:
1467
1468		CONFIG_ATMEL_LCD:
1469
1470			HITACHI TX09D70VM1CCA, 3.5", 240x320.
1471
1472		CONFIG_NEC_NL6448AC33:
1473
1474			NEC NL6448AC33-18. Active, color, single scan.
1475
1476		CONFIG_NEC_NL6448BC20
1477
1478			NEC NL6448BC20-08. 6.5", 640x480.
1479			Active, color, single scan.
1480
1481		CONFIG_NEC_NL6448BC33_54
1482
1483			NEC NL6448BC33-54. 10.4", 640x480.
1484			Active, color, single scan.
1485
1486		CONFIG_SHARP_16x9
1487
1488			Sharp 320x240. Active, color, single scan.
1489			It isn't 16x9, and I am not sure what it is.
1490
1491		CONFIG_SHARP_LQ64D341
1492
1493			Sharp LQ64D341 display, 640x480.
1494			Active, color, single scan.
1495
1496		CONFIG_HLD1045
1497
1498			HLD1045 display, 640x480.
1499			Active, color, single scan.
1500
1501		CONFIG_OPTREX_BW
1502
1503			Optrex	 CBL50840-2 NF-FW 99 22 M5
1504			or
1505			Hitachi	 LMG6912RPFC-00T
1506			or
1507			Hitachi	 SP14Q002
1508
1509			320x240. Black & white.
1510
1511		CONFIG_LCD_ALIGNMENT
1512
1513		Normally the LCD is page-aligned (typically 4KB). If this is
1514		defined then the LCD will be aligned to this value instead.
1515		For ARM it is sometimes useful to use MMU_SECTION_SIZE
1516		here, since it is cheaper to change data cache settings on
1517		a per-section basis.
1518
1519
1520		CONFIG_LCD_ROTATION
1521
1522		Sometimes, for example if the display is mounted in portrait
1523		mode or even if it's mounted landscape but rotated by 180degree,
1524		we need to rotate our content of the display relative to the
1525		framebuffer, so that user can read the messages which are
1526		printed out.
1527		Once CONFIG_LCD_ROTATION is defined, the lcd_console will be
1528		initialized with a given rotation from "vl_rot" out of
1529		"vidinfo_t" which is provided by the board specific code.
1530		The value for vl_rot is coded as following (matching to
1531		fbcon=rotate:<n> linux-kernel commandline):
1532		0 = no rotation respectively 0 degree
1533		1 = 90 degree rotation
1534		2 = 180 degree rotation
1535		3 = 270 degree rotation
1536
1537		If CONFIG_LCD_ROTATION is not defined, the console will be
1538		initialized with 0degree rotation.
1539
1540		CONFIG_LCD_BMP_RLE8
1541
1542		Support drawing of RLE8-compressed bitmaps on the LCD.
1543
1544		CONFIG_I2C_EDID
1545
1546		Enables an 'i2c edid' command which can read EDID
1547		information over I2C from an attached LCD display.
1548
1549- Splash Screen Support: CONFIG_SPLASH_SCREEN
1550
1551		If this option is set, the environment is checked for
1552		a variable "splashimage". If found, the usual display
1553		of logo, copyright and system information on the LCD
1554		is suppressed and the BMP image at the address
1555		specified in "splashimage" is loaded instead. The
1556		console is redirected to the "nulldev", too. This
1557		allows for a "silent" boot where a splash screen is
1558		loaded very quickly after power-on.
1559
1560		CONFIG_SPLASHIMAGE_GUARD
1561
1562		If this option is set, then U-Boot will prevent the environment
1563		variable "splashimage" from being set to a problematic address
1564		(see doc/README.displaying-bmps).
1565		This option is useful for targets where, due to alignment
1566		restrictions, an improperly aligned BMP image will cause a data
1567		abort. If you think you will not have problems with unaligned
1568		accesses (for example because your toolchain prevents them)
1569		there is no need to set this option.
1570
1571		CONFIG_SPLASH_SCREEN_ALIGN
1572
1573		If this option is set the splash image can be freely positioned
1574		on the screen. Environment variable "splashpos" specifies the
1575		position as "x,y". If a positive number is given it is used as
1576		number of pixel from left/top. If a negative number is given it
1577		is used as number of pixel from right/bottom. You can also
1578		specify 'm' for centering the image.
1579
1580		Example:
1581		setenv splashpos m,m
1582			=> image at center of screen
1583
1584		setenv splashpos 30,20
1585			=> image at x = 30 and y = 20
1586
1587		setenv splashpos -10,m
1588			=> vertically centered image
1589			   at x = dspWidth - bmpWidth - 9
1590
1591- Gzip compressed BMP image support: CONFIG_VIDEO_BMP_GZIP
1592
1593		If this option is set, additionally to standard BMP
1594		images, gzipped BMP images can be displayed via the
1595		splashscreen support or the bmp command.
1596
1597- Run length encoded BMP image (RLE8) support: CONFIG_VIDEO_BMP_RLE8
1598
1599		If this option is set, 8-bit RLE compressed BMP images
1600		can be displayed via the splashscreen support or the
1601		bmp command.
1602
1603- Compression support:
1604		CONFIG_GZIP
1605
1606		Enabled by default to support gzip compressed images.
1607
1608		CONFIG_BZIP2
1609
1610		If this option is set, support for bzip2 compressed
1611		images is included. If not, only uncompressed and gzip
1612		compressed images are supported.
1613
1614		NOTE: the bzip2 algorithm requires a lot of RAM, so
1615		the malloc area (as defined by CONFIG_SYS_MALLOC_LEN) should
1616		be at least 4MB.
1617
1618- MII/PHY support:
1619		CONFIG_PHY_ADDR
1620
1621		The address of PHY on MII bus.
1622
1623		CONFIG_PHY_CLOCK_FREQ (ppc4xx)
1624
1625		The clock frequency of the MII bus
1626
1627		CONFIG_PHY_RESET_DELAY
1628
1629		Some PHY like Intel LXT971A need extra delay after
1630		reset before any MII register access is possible.
1631		For such PHY, set this option to the usec delay
1632		required. (minimum 300usec for LXT971A)
1633
1634		CONFIG_PHY_CMD_DELAY (ppc4xx)
1635
1636		Some PHY like Intel LXT971A need extra delay after
1637		command issued before MII status register can be read
1638
1639- IP address:
1640		CONFIG_IPADDR
1641
1642		Define a default value for the IP address to use for
1643		the default Ethernet interface, in case this is not
1644		determined through e.g. bootp.
1645		(Environment variable "ipaddr")
1646
1647- Server IP address:
1648		CONFIG_SERVERIP
1649
1650		Defines a default value for the IP address of a TFTP
1651		server to contact when using the "tftboot" command.
1652		(Environment variable "serverip")
1653
1654		CONFIG_KEEP_SERVERADDR
1655
1656		Keeps the server's MAC address, in the env 'serveraddr'
1657		for passing to bootargs (like Linux's netconsole option)
1658
1659- Gateway IP address:
1660		CONFIG_GATEWAYIP
1661
1662		Defines a default value for the IP address of the
1663		default router where packets to other networks are
1664		sent to.
1665		(Environment variable "gatewayip")
1666
1667- Subnet mask:
1668		CONFIG_NETMASK
1669
1670		Defines a default value for the subnet mask (or
1671		routing prefix) which is used to determine if an IP
1672		address belongs to the local subnet or needs to be
1673		forwarded through a router.
1674		(Environment variable "netmask")
1675
1676- Multicast TFTP Mode:
1677		CONFIG_MCAST_TFTP
1678
1679		Defines whether you want to support multicast TFTP as per
1680		rfc-2090; for example to work with atftp.  Lets lots of targets
1681		tftp down the same boot image concurrently.  Note: the Ethernet
1682		driver in use must provide a function: mcast() to join/leave a
1683		multicast group.
1684
1685- BOOTP Recovery Mode:
1686		CONFIG_BOOTP_RANDOM_DELAY
1687
1688		If you have many targets in a network that try to
1689		boot using BOOTP, you may want to avoid that all
1690		systems send out BOOTP requests at precisely the same
1691		moment (which would happen for instance at recovery
1692		from a power failure, when all systems will try to
1693		boot, thus flooding the BOOTP server. Defining
1694		CONFIG_BOOTP_RANDOM_DELAY causes a random delay to be
1695		inserted before sending out BOOTP requests. The
1696		following delays are inserted then:
1697
1698		1st BOOTP request:	delay 0 ... 1 sec
1699		2nd BOOTP request:	delay 0 ... 2 sec
1700		3rd BOOTP request:	delay 0 ... 4 sec
1701		4th and following
1702		BOOTP requests:		delay 0 ... 8 sec
1703
1704		CONFIG_BOOTP_ID_CACHE_SIZE
1705
1706		BOOTP packets are uniquely identified using a 32-bit ID. The
1707		server will copy the ID from client requests to responses and
1708		U-Boot will use this to determine if it is the destination of
1709		an incoming response. Some servers will check that addresses
1710		aren't in use before handing them out (usually using an ARP
1711		ping) and therefore take up to a few hundred milliseconds to
1712		respond. Network congestion may also influence the time it
1713		takes for a response to make it back to the client. If that
1714		time is too long, U-Boot will retransmit requests. In order
1715		to allow earlier responses to still be accepted after these
1716		retransmissions, U-Boot's BOOTP client keeps a small cache of
1717		IDs. The CONFIG_BOOTP_ID_CACHE_SIZE controls the size of this
1718		cache. The default is to keep IDs for up to four outstanding
1719		requests. Increasing this will allow U-Boot to accept offers
1720		from a BOOTP client in networks with unusually high latency.
1721
1722- DHCP Advanced Options:
1723		You can fine tune the DHCP functionality by defining
1724		CONFIG_BOOTP_* symbols:
1725
1726		CONFIG_BOOTP_SUBNETMASK
1727		CONFIG_BOOTP_GATEWAY
1728		CONFIG_BOOTP_HOSTNAME
1729		CONFIG_BOOTP_NISDOMAIN
1730		CONFIG_BOOTP_BOOTPATH
1731		CONFIG_BOOTP_BOOTFILESIZE
1732		CONFIG_BOOTP_DNS
1733		CONFIG_BOOTP_DNS2
1734		CONFIG_BOOTP_SEND_HOSTNAME
1735		CONFIG_BOOTP_NTPSERVER
1736		CONFIG_BOOTP_TIMEOFFSET
1737		CONFIG_BOOTP_VENDOREX
1738		CONFIG_BOOTP_MAY_FAIL
1739
1740		CONFIG_BOOTP_SERVERIP - TFTP server will be the serverip
1741		environment variable, not the BOOTP server.
1742
1743		CONFIG_BOOTP_MAY_FAIL - If the DHCP server is not found
1744		after the configured retry count, the call will fail
1745		instead of starting over.  This can be used to fail over
1746		to Link-local IP address configuration if the DHCP server
1747		is not available.
1748
1749		CONFIG_BOOTP_DNS2 - If a DHCP client requests the DNS
1750		serverip from a DHCP server, it is possible that more
1751		than one DNS serverip is offered to the client.
1752		If CONFIG_BOOTP_DNS2 is enabled, the secondary DNS
1753		serverip will be stored in the additional environment
1754		variable "dnsip2". The first DNS serverip is always
1755		stored in the variable "dnsip", when CONFIG_BOOTP_DNS
1756		is defined.
1757
1758		CONFIG_BOOTP_SEND_HOSTNAME - Some DHCP servers are capable
1759		to do a dynamic update of a DNS server. To do this, they
1760		need the hostname of the DHCP requester.
1761		If CONFIG_BOOTP_SEND_HOSTNAME is defined, the content
1762		of the "hostname" environment variable is passed as
1763		option 12 to the DHCP server.
1764
1765		CONFIG_BOOTP_DHCP_REQUEST_DELAY
1766
1767		A 32bit value in microseconds for a delay between
1768		receiving a "DHCP Offer" and sending the "DHCP Request".
1769		This fixes a problem with certain DHCP servers that don't
1770		respond 100% of the time to a "DHCP request". E.g. On an
1771		AT91RM9200 processor running at 180MHz, this delay needed
1772		to be *at least* 15,000 usec before a Windows Server 2003
1773		DHCP server would reply 100% of the time. I recommend at
1774		least 50,000 usec to be safe. The alternative is to hope
1775		that one of the retries will be successful but note that
1776		the DHCP timeout and retry process takes a longer than
1777		this delay.
1778
1779 - Link-local IP address negotiation:
1780		Negotiate with other link-local clients on the local network
1781		for an address that doesn't require explicit configuration.
1782		This is especially useful if a DHCP server cannot be guaranteed
1783		to exist in all environments that the device must operate.
1784
1785		See doc/README.link-local for more information.
1786
1787 - CDP Options:
1788		CONFIG_CDP_DEVICE_ID
1789
1790		The device id used in CDP trigger frames.
1791
1792		CONFIG_CDP_DEVICE_ID_PREFIX
1793
1794		A two character string which is prefixed to the MAC address
1795		of the device.
1796
1797		CONFIG_CDP_PORT_ID
1798
1799		A printf format string which contains the ascii name of
1800		the port. Normally is set to "eth%d" which sets
1801		eth0 for the first Ethernet, eth1 for the second etc.
1802
1803		CONFIG_CDP_CAPABILITIES
1804
1805		A 32bit integer which indicates the device capabilities;
1806		0x00000010 for a normal host which does not forwards.
1807
1808		CONFIG_CDP_VERSION
1809
1810		An ascii string containing the version of the software.
1811
1812		CONFIG_CDP_PLATFORM
1813
1814		An ascii string containing the name of the platform.
1815
1816		CONFIG_CDP_TRIGGER
1817
1818		A 32bit integer sent on the trigger.
1819
1820		CONFIG_CDP_POWER_CONSUMPTION
1821
1822		A 16bit integer containing the power consumption of the
1823		device in .1 of milliwatts.
1824
1825		CONFIG_CDP_APPLIANCE_VLAN_TYPE
1826
1827		A byte containing the id of the VLAN.
1828
1829- Status LED:	CONFIG_LED_STATUS
1830
1831		Several configurations allow to display the current
1832		status using a LED. For instance, the LED will blink
1833		fast while running U-Boot code, stop blinking as
1834		soon as a reply to a BOOTP request was received, and
1835		start blinking slow once the Linux kernel is running
1836		(supported by a status LED driver in the Linux
1837		kernel). Defining CONFIG_LED_STATUS enables this
1838		feature in U-Boot.
1839
1840		Additional options:
1841
1842		CONFIG_LED_STATUS_GPIO
1843		The status LED can be connected to a GPIO pin.
1844		In such cases, the gpio_led driver can be used as a
1845		status LED backend implementation. Define CONFIG_LED_STATUS_GPIO
1846		to include the gpio_led driver in the U-Boot binary.
1847
1848		CONFIG_GPIO_LED_INVERTED_TABLE
1849		Some GPIO connected LEDs may have inverted polarity in which
1850		case the GPIO high value corresponds to LED off state and
1851		GPIO low value corresponds to LED on state.
1852		In such cases CONFIG_GPIO_LED_INVERTED_TABLE may be defined
1853		with a list of GPIO LEDs that have inverted polarity.
1854
1855- I2C Support:	CONFIG_SYS_I2C
1856
1857		This enable the NEW i2c subsystem, and will allow you to use
1858		i2c commands at the u-boot command line (as long as you set
1859		CONFIG_CMD_I2C in CONFIG_COMMANDS) and communicate with i2c
1860		based realtime clock chips or other i2c devices. See
1861		common/cmd_i2c.c for a description of the command line
1862		interface.
1863
1864		ported i2c driver to the new framework:
1865		- drivers/i2c/soft_i2c.c:
1866		  - activate first bus with CONFIG_SYS_I2C_SOFT define
1867		    CONFIG_SYS_I2C_SOFT_SPEED and CONFIG_SYS_I2C_SOFT_SLAVE
1868		    for defining speed and slave address
1869		  - activate second bus with I2C_SOFT_DECLARATIONS2 define
1870		    CONFIG_SYS_I2C_SOFT_SPEED_2 and CONFIG_SYS_I2C_SOFT_SLAVE_2
1871		    for defining speed and slave address
1872		  - activate third bus with I2C_SOFT_DECLARATIONS3 define
1873		    CONFIG_SYS_I2C_SOFT_SPEED_3 and CONFIG_SYS_I2C_SOFT_SLAVE_3
1874		    for defining speed and slave address
1875		  - activate fourth bus with I2C_SOFT_DECLARATIONS4 define
1876		    CONFIG_SYS_I2C_SOFT_SPEED_4 and CONFIG_SYS_I2C_SOFT_SLAVE_4
1877		    for defining speed and slave address
1878
1879		- drivers/i2c/fsl_i2c.c:
1880		  - activate i2c driver with CONFIG_SYS_I2C_FSL
1881		    define CONFIG_SYS_FSL_I2C_OFFSET for setting the register
1882		    offset CONFIG_SYS_FSL_I2C_SPEED for the i2c speed and
1883		    CONFIG_SYS_FSL_I2C_SLAVE for the slave addr of the first
1884		    bus.
1885		  - If your board supports a second fsl i2c bus, define
1886		    CONFIG_SYS_FSL_I2C2_OFFSET for the register offset
1887		    CONFIG_SYS_FSL_I2C2_SPEED for the speed and
1888		    CONFIG_SYS_FSL_I2C2_SLAVE for the slave address of the
1889		    second bus.
1890
1891		- drivers/i2c/tegra_i2c.c:
1892		  - activate this driver with CONFIG_SYS_I2C_TEGRA
1893		  - This driver adds 4 i2c buses with a fix speed from
1894		    100000 and the slave addr 0!
1895
1896		- drivers/i2c/ppc4xx_i2c.c
1897		  - activate this driver with CONFIG_SYS_I2C_PPC4XX
1898		  - CONFIG_SYS_I2C_PPC4XX_CH0 activate hardware channel 0
1899		  - CONFIG_SYS_I2C_PPC4XX_CH1 activate hardware channel 1
1900
1901		- drivers/i2c/i2c_mxc.c
1902		  - activate this driver with CONFIG_SYS_I2C_MXC
1903		  - enable bus 1 with CONFIG_SYS_I2C_MXC_I2C1
1904		  - enable bus 2 with CONFIG_SYS_I2C_MXC_I2C2
1905		  - enable bus 3 with CONFIG_SYS_I2C_MXC_I2C3
1906		  - enable bus 4 with CONFIG_SYS_I2C_MXC_I2C4
1907		  - define speed for bus 1 with CONFIG_SYS_MXC_I2C1_SPEED
1908		  - define slave for bus 1 with CONFIG_SYS_MXC_I2C1_SLAVE
1909		  - define speed for bus 2 with CONFIG_SYS_MXC_I2C2_SPEED
1910		  - define slave for bus 2 with CONFIG_SYS_MXC_I2C2_SLAVE
1911		  - define speed for bus 3 with CONFIG_SYS_MXC_I2C3_SPEED
1912		  - define slave for bus 3 with CONFIG_SYS_MXC_I2C3_SLAVE
1913		  - define speed for bus 4 with CONFIG_SYS_MXC_I2C4_SPEED
1914		  - define slave for bus 4 with CONFIG_SYS_MXC_I2C4_SLAVE
1915		If those defines are not set, default value is 100000
1916		for speed, and 0 for slave.
1917
1918		- drivers/i2c/rcar_i2c.c:
1919		  - activate this driver with CONFIG_SYS_I2C_RCAR
1920		  - This driver adds 4 i2c buses
1921
1922		  - CONFIG_SYS_RCAR_I2C0_BASE for setting the register channel 0
1923		  - CONFIG_SYS_RCAR_I2C0_SPEED for for the speed channel 0
1924		  - CONFIG_SYS_RCAR_I2C1_BASE for setting the register channel 1
1925		  - CONFIG_SYS_RCAR_I2C1_SPEED for for the speed channel 1
1926		  - CONFIG_SYS_RCAR_I2C2_BASE for setting the register channel 2
1927		  - CONFIG_SYS_RCAR_I2C2_SPEED for for the speed channel 2
1928		  - CONFIG_SYS_RCAR_I2C3_BASE for setting the register channel 3
1929		  - CONFIG_SYS_RCAR_I2C3_SPEED for for the speed channel 3
1930		  - CONFIF_SYS_RCAR_I2C_NUM_CONTROLLERS for number of i2c buses
1931
1932		- drivers/i2c/sh_i2c.c:
1933		  - activate this driver with CONFIG_SYS_I2C_SH
1934		  - This driver adds from 2 to 5 i2c buses
1935
1936		  - CONFIG_SYS_I2C_SH_BASE0 for setting the register channel 0
1937		  - CONFIG_SYS_I2C_SH_SPEED0 for for the speed channel 0
1938		  - CONFIG_SYS_I2C_SH_BASE1 for setting the register channel 1
1939		  - CONFIG_SYS_I2C_SH_SPEED1 for for the speed channel 1
1940		  - CONFIG_SYS_I2C_SH_BASE2 for setting the register channel 2
1941		  - CONFIG_SYS_I2C_SH_SPEED2 for for the speed channel 2
1942		  - CONFIG_SYS_I2C_SH_BASE3 for setting the register channel 3
1943		  - CONFIG_SYS_I2C_SH_SPEED3 for for the speed channel 3
1944		  - CONFIG_SYS_I2C_SH_BASE4 for setting the register channel 4
1945		  - CONFIG_SYS_I2C_SH_SPEED4 for for the speed channel 4
1946		  - CONFIG_SYS_I2C_SH_NUM_CONTROLLERS for number of i2c buses
1947
1948		- drivers/i2c/omap24xx_i2c.c
1949		  - activate this driver with CONFIG_SYS_I2C_OMAP24XX
1950		  - CONFIG_SYS_OMAP24_I2C_SPEED speed channel 0
1951		  - CONFIG_SYS_OMAP24_I2C_SLAVE slave addr channel 0
1952		  - CONFIG_SYS_OMAP24_I2C_SPEED1 speed channel 1
1953		  - CONFIG_SYS_OMAP24_I2C_SLAVE1 slave addr channel 1
1954		  - CONFIG_SYS_OMAP24_I2C_SPEED2 speed channel 2
1955		  - CONFIG_SYS_OMAP24_I2C_SLAVE2 slave addr channel 2
1956		  - CONFIG_SYS_OMAP24_I2C_SPEED3 speed channel 3
1957		  - CONFIG_SYS_OMAP24_I2C_SLAVE3 slave addr channel 3
1958		  - CONFIG_SYS_OMAP24_I2C_SPEED4 speed channel 4
1959		  - CONFIG_SYS_OMAP24_I2C_SLAVE4 slave addr channel 4
1960
1961		- drivers/i2c/zynq_i2c.c
1962		  - activate this driver with CONFIG_SYS_I2C_ZYNQ
1963		  - set CONFIG_SYS_I2C_ZYNQ_SPEED for speed setting
1964		  - set CONFIG_SYS_I2C_ZYNQ_SLAVE for slave addr
1965
1966		- drivers/i2c/s3c24x0_i2c.c:
1967		  - activate this driver with CONFIG_SYS_I2C_S3C24X0
1968		  - This driver adds i2c buses (11 for Exynos5250, Exynos5420
1969		    9 i2c buses for Exynos4 and 1 for S3C24X0 SoCs from Samsung)
1970		    with a fix speed from 100000 and the slave addr 0!
1971
1972		- drivers/i2c/ihs_i2c.c
1973		  - activate this driver with CONFIG_SYS_I2C_IHS
1974		  - CONFIG_SYS_I2C_IHS_CH0 activate hardware channel 0
1975		  - CONFIG_SYS_I2C_IHS_SPEED_0 speed channel 0
1976		  - CONFIG_SYS_I2C_IHS_SLAVE_0 slave addr channel 0
1977		  - CONFIG_SYS_I2C_IHS_CH1 activate hardware channel 1
1978		  - CONFIG_SYS_I2C_IHS_SPEED_1 speed channel 1
1979		  - CONFIG_SYS_I2C_IHS_SLAVE_1 slave addr channel 1
1980		  - CONFIG_SYS_I2C_IHS_CH2 activate hardware channel 2
1981		  - CONFIG_SYS_I2C_IHS_SPEED_2 speed channel 2
1982		  - CONFIG_SYS_I2C_IHS_SLAVE_2 slave addr channel 2
1983		  - CONFIG_SYS_I2C_IHS_CH3 activate hardware channel 3
1984		  - CONFIG_SYS_I2C_IHS_SPEED_3 speed channel 3
1985		  - CONFIG_SYS_I2C_IHS_SLAVE_3 slave addr channel 3
1986		  - activate dual channel with CONFIG_SYS_I2C_IHS_DUAL
1987		  - CONFIG_SYS_I2C_IHS_SPEED_0_1 speed channel 0_1
1988		  - CONFIG_SYS_I2C_IHS_SLAVE_0_1 slave addr channel 0_1
1989		  - CONFIG_SYS_I2C_IHS_SPEED_1_1 speed channel 1_1
1990		  - CONFIG_SYS_I2C_IHS_SLAVE_1_1 slave addr channel 1_1
1991		  - CONFIG_SYS_I2C_IHS_SPEED_2_1 speed channel 2_1
1992		  - CONFIG_SYS_I2C_IHS_SLAVE_2_1 slave addr channel 2_1
1993		  - CONFIG_SYS_I2C_IHS_SPEED_3_1 speed channel 3_1
1994		  - CONFIG_SYS_I2C_IHS_SLAVE_3_1 slave addr channel 3_1
1995
1996		additional defines:
1997
1998		CONFIG_SYS_NUM_I2C_BUSES
1999		Hold the number of i2c buses you want to use.
2000
2001		CONFIG_SYS_I2C_DIRECT_BUS
2002		define this, if you don't use i2c muxes on your hardware.
2003		if CONFIG_SYS_I2C_MAX_HOPS is not defined or == 0 you can
2004		omit this define.
2005
2006		CONFIG_SYS_I2C_MAX_HOPS
2007		define how many muxes are maximal consecutively connected
2008		on one i2c bus. If you not use i2c muxes, omit this
2009		define.
2010
2011		CONFIG_SYS_I2C_BUSES
2012		hold a list of buses you want to use, only used if
2013		CONFIG_SYS_I2C_DIRECT_BUS is not defined, for example
2014		a board with CONFIG_SYS_I2C_MAX_HOPS = 1 and
2015		CONFIG_SYS_NUM_I2C_BUSES = 9:
2016
2017		 CONFIG_SYS_I2C_BUSES	{{0, {I2C_NULL_HOP}}, \
2018					{0, {{I2C_MUX_PCA9547, 0x70, 1}}}, \
2019					{0, {{I2C_MUX_PCA9547, 0x70, 2}}}, \
2020					{0, {{I2C_MUX_PCA9547, 0x70, 3}}}, \
2021					{0, {{I2C_MUX_PCA9547, 0x70, 4}}}, \
2022					{0, {{I2C_MUX_PCA9547, 0x70, 5}}}, \
2023					{1, {I2C_NULL_HOP}}, \
2024					{1, {{I2C_MUX_PCA9544, 0x72, 1}}}, \
2025					{1, {{I2C_MUX_PCA9544, 0x72, 2}}}, \
2026					}
2027
2028		which defines
2029			bus 0 on adapter 0 without a mux
2030			bus 1 on adapter 0 with a PCA9547 on address 0x70 port 1
2031			bus 2 on adapter 0 with a PCA9547 on address 0x70 port 2
2032			bus 3 on adapter 0 with a PCA9547 on address 0x70 port 3
2033			bus 4 on adapter 0 with a PCA9547 on address 0x70 port 4
2034			bus 5 on adapter 0 with a PCA9547 on address 0x70 port 5
2035			bus 6 on adapter 1 without a mux
2036			bus 7 on adapter 1 with a PCA9544 on address 0x72 port 1
2037			bus 8 on adapter 1 with a PCA9544 on address 0x72 port 2
2038
2039		If you do not have i2c muxes on your board, omit this define.
2040
2041- Legacy I2C Support:
2042		If you use the software i2c interface (CONFIG_SYS_I2C_SOFT)
2043		then the following macros need to be defined (examples are
2044		from include/configs/lwmon.h):
2045
2046		I2C_INIT
2047
2048		(Optional). Any commands necessary to enable the I2C
2049		controller or configure ports.
2050
2051		eg: #define I2C_INIT (immr->im_cpm.cp_pbdir |=	PB_SCL)
2052
2053		I2C_ACTIVE
2054
2055		The code necessary to make the I2C data line active
2056		(driven).  If the data line is open collector, this
2057		define can be null.
2058
2059		eg: #define I2C_ACTIVE (immr->im_cpm.cp_pbdir |=  PB_SDA)
2060
2061		I2C_TRISTATE
2062
2063		The code necessary to make the I2C data line tri-stated
2064		(inactive).  If the data line is open collector, this
2065		define can be null.
2066
2067		eg: #define I2C_TRISTATE (immr->im_cpm.cp_pbdir &= ~PB_SDA)
2068
2069		I2C_READ
2070
2071		Code that returns true if the I2C data line is high,
2072		false if it is low.
2073
2074		eg: #define I2C_READ ((immr->im_cpm.cp_pbdat & PB_SDA) != 0)
2075
2076		I2C_SDA(bit)
2077
2078		If <bit> is true, sets the I2C data line high. If it
2079		is false, it clears it (low).
2080
2081		eg: #define I2C_SDA(bit) \
2082			if(bit) immr->im_cpm.cp_pbdat |=  PB_SDA; \
2083			else	immr->im_cpm.cp_pbdat &= ~PB_SDA
2084
2085		I2C_SCL(bit)
2086
2087		If <bit> is true, sets the I2C clock line high. If it
2088		is false, it clears it (low).
2089
2090		eg: #define I2C_SCL(bit) \
2091			if(bit) immr->im_cpm.cp_pbdat |=  PB_SCL; \
2092			else	immr->im_cpm.cp_pbdat &= ~PB_SCL
2093
2094		I2C_DELAY
2095
2096		This delay is invoked four times per clock cycle so this
2097		controls the rate of data transfer.  The data rate thus
2098		is 1 / (I2C_DELAY * 4). Often defined to be something
2099		like:
2100
2101		#define I2C_DELAY  udelay(2)
2102
2103		CONFIG_SOFT_I2C_GPIO_SCL / CONFIG_SOFT_I2C_GPIO_SDA
2104
2105		If your arch supports the generic GPIO framework (asm/gpio.h),
2106		then you may alternatively define the two GPIOs that are to be
2107		used as SCL / SDA.  Any of the previous I2C_xxx macros will
2108		have GPIO-based defaults assigned to them as appropriate.
2109
2110		You should define these to the GPIO value as given directly to
2111		the generic GPIO functions.
2112
2113		CONFIG_SYS_I2C_INIT_BOARD
2114
2115		When a board is reset during an i2c bus transfer
2116		chips might think that the current transfer is still
2117		in progress. On some boards it is possible to access
2118		the i2c SCLK line directly, either by using the
2119		processor pin as a GPIO or by having a second pin
2120		connected to the bus. If this option is defined a
2121		custom i2c_init_board() routine in boards/xxx/board.c
2122		is run early in the boot sequence.
2123
2124		CONFIG_I2C_MULTI_BUS
2125
2126		This option allows the use of multiple I2C buses, each of which
2127		must have a controller.	 At any point in time, only one bus is
2128		active.	 To switch to a different bus, use the 'i2c dev' command.
2129		Note that bus numbering is zero-based.
2130
2131		CONFIG_SYS_I2C_NOPROBES
2132
2133		This option specifies a list of I2C devices that will be skipped
2134		when the 'i2c probe' command is issued.	 If CONFIG_I2C_MULTI_BUS
2135		is set, specify a list of bus-device pairs.  Otherwise, specify
2136		a 1D array of device addresses
2137
2138		e.g.
2139			#undef	CONFIG_I2C_MULTI_BUS
2140			#define CONFIG_SYS_I2C_NOPROBES {0x50,0x68}
2141
2142		will skip addresses 0x50 and 0x68 on a board with one I2C bus
2143
2144			#define CONFIG_I2C_MULTI_BUS
2145			#define CONFIG_SYS_I2C_NOPROBES	{{0,0x50},{0,0x68},{1,0x54}}
2146
2147		will skip addresses 0x50 and 0x68 on bus 0 and address 0x54 on bus 1
2148
2149		CONFIG_SYS_SPD_BUS_NUM
2150
2151		If defined, then this indicates the I2C bus number for DDR SPD.
2152		If not defined, then U-Boot assumes that SPD is on I2C bus 0.
2153
2154		CONFIG_SYS_RTC_BUS_NUM
2155
2156		If defined, then this indicates the I2C bus number for the RTC.
2157		If not defined, then U-Boot assumes that RTC is on I2C bus 0.
2158
2159		CONFIG_SOFT_I2C_READ_REPEATED_START
2160
2161		defining this will force the i2c_read() function in
2162		the soft_i2c driver to perform an I2C repeated start
2163		between writing the address pointer and reading the
2164		data.  If this define is omitted the default behaviour
2165		of doing a stop-start sequence will be used.  Most I2C
2166		devices can use either method, but some require one or
2167		the other.
2168
2169- SPI Support:	CONFIG_SPI
2170
2171		Enables SPI driver (so far only tested with
2172		SPI EEPROM, also an instance works with Crystal A/D and
2173		D/As on the SACSng board)
2174
2175		CONFIG_SH_SPI
2176
2177		Enables the driver for SPI controller on SuperH. Currently
2178		only SH7757 is supported.
2179
2180		CONFIG_SOFT_SPI
2181
2182		Enables a software (bit-bang) SPI driver rather than
2183		using hardware support. This is a general purpose
2184		driver that only requires three general I/O port pins
2185		(two outputs, one input) to function. If this is
2186		defined, the board configuration must define several
2187		SPI configuration items (port pins to use, etc). For
2188		an example, see include/configs/sacsng.h.
2189
2190		CONFIG_HARD_SPI
2191
2192		Enables a hardware SPI driver for general-purpose reads
2193		and writes.  As with CONFIG_SOFT_SPI, the board configuration
2194		must define a list of chip-select function pointers.
2195		Currently supported on some MPC8xxx processors.	 For an
2196		example, see include/configs/mpc8349emds.h.
2197
2198		CONFIG_MXC_SPI
2199
2200		Enables the driver for the SPI controllers on i.MX and MXC
2201		SoCs. Currently i.MX31/35/51 are supported.
2202
2203		CONFIG_SYS_SPI_MXC_WAIT
2204		Timeout for waiting until spi transfer completed.
2205		default: (CONFIG_SYS_HZ/100)     /* 10 ms */
2206
2207- FPGA Support: CONFIG_FPGA
2208
2209		Enables FPGA subsystem.
2210
2211		CONFIG_FPGA_<vendor>
2212
2213		Enables support for specific chip vendors.
2214		(ALTERA, XILINX)
2215
2216		CONFIG_FPGA_<family>
2217
2218		Enables support for FPGA family.
2219		(SPARTAN2, SPARTAN3, VIRTEX2, CYCLONE2, ACEX1K, ACEX)
2220
2221		CONFIG_FPGA_COUNT
2222
2223		Specify the number of FPGA devices to support.
2224
2225		CONFIG_SYS_FPGA_PROG_FEEDBACK
2226
2227		Enable printing of hash marks during FPGA configuration.
2228
2229		CONFIG_SYS_FPGA_CHECK_BUSY
2230
2231		Enable checks on FPGA configuration interface busy
2232		status by the configuration function. This option
2233		will require a board or device specific function to
2234		be written.
2235
2236		CONFIG_FPGA_DELAY
2237
2238		If defined, a function that provides delays in the FPGA
2239		configuration driver.
2240
2241		CONFIG_SYS_FPGA_CHECK_CTRLC
2242		Allow Control-C to interrupt FPGA configuration
2243
2244		CONFIG_SYS_FPGA_CHECK_ERROR
2245
2246		Check for configuration errors during FPGA bitfile
2247		loading. For example, abort during Virtex II
2248		configuration if the INIT_B line goes low (which
2249		indicated a CRC error).
2250
2251		CONFIG_SYS_FPGA_WAIT_INIT
2252
2253		Maximum time to wait for the INIT_B line to de-assert
2254		after PROB_B has been de-asserted during a Virtex II
2255		FPGA configuration sequence. The default time is 500
2256		ms.
2257
2258		CONFIG_SYS_FPGA_WAIT_BUSY
2259
2260		Maximum time to wait for BUSY to de-assert during
2261		Virtex II FPGA configuration. The default is 5 ms.
2262
2263		CONFIG_SYS_FPGA_WAIT_CONFIG
2264
2265		Time to wait after FPGA configuration. The default is
2266		200 ms.
2267
2268- Configuration Management:
2269		CONFIG_BUILD_TARGET
2270
2271		Some SoCs need special image types (e.g. U-Boot binary
2272		with a special header) as build targets. By defining
2273		CONFIG_BUILD_TARGET in the SoC / board header, this
2274		special image will be automatically built upon calling
2275		make / buildman.
2276
2277		CONFIG_IDENT_STRING
2278
2279		If defined, this string will be added to the U-Boot
2280		version information (U_BOOT_VERSION)
2281
2282- Vendor Parameter Protection:
2283
2284		U-Boot considers the values of the environment
2285		variables "serial#" (Board Serial Number) and
2286		"ethaddr" (Ethernet Address) to be parameters that
2287		are set once by the board vendor / manufacturer, and
2288		protects these variables from casual modification by
2289		the user. Once set, these variables are read-only,
2290		and write or delete attempts are rejected. You can
2291		change this behaviour:
2292
2293		If CONFIG_ENV_OVERWRITE is #defined in your config
2294		file, the write protection for vendor parameters is
2295		completely disabled. Anybody can change or delete
2296		these parameters.
2297
2298		Alternatively, if you define _both_ an ethaddr in the
2299		default env _and_ CONFIG_OVERWRITE_ETHADDR_ONCE, a default
2300		Ethernet address is installed in the environment,
2301		which can be changed exactly ONCE by the user. [The
2302		serial# is unaffected by this, i. e. it remains
2303		read-only.]
2304
2305		The same can be accomplished in a more flexible way
2306		for any variable by configuring the type of access
2307		to allow for those variables in the ".flags" variable
2308		or define CONFIG_ENV_FLAGS_LIST_STATIC.
2309
2310- Protected RAM:
2311		CONFIG_PRAM
2312
2313		Define this variable to enable the reservation of
2314		"protected RAM", i. e. RAM which is not overwritten
2315		by U-Boot. Define CONFIG_PRAM to hold the number of
2316		kB you want to reserve for pRAM. You can overwrite
2317		this default value by defining an environment
2318		variable "pram" to the number of kB you want to
2319		reserve. Note that the board info structure will
2320		still show the full amount of RAM. If pRAM is
2321		reserved, a new environment variable "mem" will
2322		automatically be defined to hold the amount of
2323		remaining RAM in a form that can be passed as boot
2324		argument to Linux, for instance like that:
2325
2326			setenv bootargs ... mem=\${mem}
2327			saveenv
2328
2329		This way you can tell Linux not to use this memory,
2330		either, which results in a memory region that will
2331		not be affected by reboots.
2332
2333		*WARNING* If your board configuration uses automatic
2334		detection of the RAM size, you must make sure that
2335		this memory test is non-destructive. So far, the
2336		following board configurations are known to be
2337		"pRAM-clean":
2338
2339			IVMS8, IVML24, SPD8xx,
2340			HERMES, IP860, RPXlite, LWMON,
2341			FLAGADM
2342
2343- Access to physical memory region (> 4GB)
2344		Some basic support is provided for operations on memory not
2345		normally accessible to U-Boot - e.g. some architectures
2346		support access to more than 4GB of memory on 32-bit
2347		machines using physical address extension or similar.
2348		Define CONFIG_PHYSMEM to access this basic support, which
2349		currently only supports clearing the memory.
2350
2351- Error Recovery:
2352		CONFIG_PANIC_HANG
2353
2354		Define this variable to stop the system in case of a
2355		fatal error, so that you have to reset it manually.
2356		This is probably NOT a good idea for an embedded
2357		system where you want the system to reboot
2358		automatically as fast as possible, but it may be
2359		useful during development since you can try to debug
2360		the conditions that lead to the situation.
2361
2362		CONFIG_NET_RETRY_COUNT
2363
2364		This variable defines the number of retries for
2365		network operations like ARP, RARP, TFTP, or BOOTP
2366		before giving up the operation. If not defined, a
2367		default value of 5 is used.
2368
2369		CONFIG_ARP_TIMEOUT
2370
2371		Timeout waiting for an ARP reply in milliseconds.
2372
2373		CONFIG_NFS_TIMEOUT
2374
2375		Timeout in milliseconds used in NFS protocol.
2376		If you encounter "ERROR: Cannot umount" in nfs command,
2377		try longer timeout such as
2378		#define CONFIG_NFS_TIMEOUT 10000UL
2379
2380- Command Interpreter:
2381		CONFIG_AUTO_COMPLETE
2382
2383		Enable auto completion of commands using TAB.
2384
2385		CONFIG_SYS_PROMPT_HUSH_PS2
2386
2387		This defines the secondary prompt string, which is
2388		printed when the command interpreter needs more input
2389		to complete a command. Usually "> ".
2390
2391	Note:
2392
2393		In the current implementation, the local variables
2394		space and global environment variables space are
2395		separated. Local variables are those you define by
2396		simply typing `name=value'. To access a local
2397		variable later on, you have write `$name' or
2398		`${name}'; to execute the contents of a variable
2399		directly type `$name' at the command prompt.
2400
2401		Global environment variables are those you use
2402		setenv/printenv to work with. To run a command stored
2403		in such a variable, you need to use the run command,
2404		and you must not use the '$' sign to access them.
2405
2406		To store commands and special characters in a
2407		variable, please use double quotation marks
2408		surrounding the whole text of the variable, instead
2409		of the backslashes before semicolons and special
2410		symbols.
2411
2412- Command Line Editing and History:
2413		CONFIG_CMDLINE_EDITING
2414
2415		Enable editing and History functions for interactive
2416		command line input operations
2417
2418- Command Line PS1/PS2 support:
2419		CONFIG_CMDLINE_PS_SUPPORT
2420
2421		Enable support for changing the command prompt string
2422		at run-time. Only static string is supported so far.
2423		The string is obtained from environment variables PS1
2424		and PS2.
2425
2426- Default Environment:
2427		CONFIG_EXTRA_ENV_SETTINGS
2428
2429		Define this to contain any number of null terminated
2430		strings (variable = value pairs) that will be part of
2431		the default environment compiled into the boot image.
2432
2433		For example, place something like this in your
2434		board's config file:
2435
2436		#define CONFIG_EXTRA_ENV_SETTINGS \
2437			"myvar1=value1\0" \
2438			"myvar2=value2\0"
2439
2440		Warning: This method is based on knowledge about the
2441		internal format how the environment is stored by the
2442		U-Boot code. This is NOT an official, exported
2443		interface! Although it is unlikely that this format
2444		will change soon, there is no guarantee either.
2445		You better know what you are doing here.
2446
2447		Note: overly (ab)use of the default environment is
2448		discouraged. Make sure to check other ways to preset
2449		the environment like the "source" command or the
2450		boot command first.
2451
2452		CONFIG_ENV_VARS_UBOOT_CONFIG
2453
2454		Define this in order to add variables describing the
2455		U-Boot build configuration to the default environment.
2456		These will be named arch, cpu, board, vendor, and soc.
2457
2458		Enabling this option will cause the following to be defined:
2459
2460		- CONFIG_SYS_ARCH
2461		- CONFIG_SYS_CPU
2462		- CONFIG_SYS_BOARD
2463		- CONFIG_SYS_VENDOR
2464		- CONFIG_SYS_SOC
2465
2466		CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
2467
2468		Define this in order to add variables describing certain
2469		run-time determined information about the hardware to the
2470		environment.  These will be named board_name, board_rev.
2471
2472		CONFIG_DELAY_ENVIRONMENT
2473
2474		Normally the environment is loaded when the board is
2475		initialised so that it is available to U-Boot. This inhibits
2476		that so that the environment is not available until
2477		explicitly loaded later by U-Boot code. With CONFIG_OF_CONTROL
2478		this is instead controlled by the value of
2479		/config/load-environment.
2480
2481- DataFlash Support:
2482		CONFIG_HAS_DATAFLASH
2483
2484		Defining this option enables DataFlash features and
2485		allows to read/write in Dataflash via the standard
2486		commands cp, md...
2487
2488- Serial Flash support
2489		CONFIG_CMD_SF
2490
2491		Defining this option enables SPI flash commands
2492		'sf probe/read/write/erase/update'.
2493
2494		Usage requires an initial 'probe' to define the serial
2495		flash parameters, followed by read/write/erase/update
2496		commands.
2497
2498		The following defaults may be provided by the platform
2499		to handle the common case when only a single serial
2500		flash is present on the system.
2501
2502		CONFIG_SF_DEFAULT_BUS		Bus identifier
2503		CONFIG_SF_DEFAULT_CS		Chip-select
2504		CONFIG_SF_DEFAULT_MODE 		(see include/spi.h)
2505		CONFIG_SF_DEFAULT_SPEED		in Hz
2506
2507		CONFIG_CMD_SF_TEST
2508
2509		Define this option to include a destructive SPI flash
2510		test ('sf test').
2511
2512- SystemACE Support:
2513		CONFIG_SYSTEMACE
2514
2515		Adding this option adds support for Xilinx SystemACE
2516		chips attached via some sort of local bus. The address
2517		of the chip must also be defined in the
2518		CONFIG_SYS_SYSTEMACE_BASE macro. For example:
2519
2520		#define CONFIG_SYSTEMACE
2521		#define CONFIG_SYS_SYSTEMACE_BASE 0xf0000000
2522
2523		When SystemACE support is added, the "ace" device type
2524		becomes available to the fat commands, i.e. fatls.
2525
2526- TFTP Fixed UDP Port:
2527		CONFIG_TFTP_PORT
2528
2529		If this is defined, the environment variable tftpsrcp
2530		is used to supply the TFTP UDP source port value.
2531		If tftpsrcp isn't defined, the normal pseudo-random port
2532		number generator is used.
2533
2534		Also, the environment variable tftpdstp is used to supply
2535		the TFTP UDP destination port value.  If tftpdstp isn't
2536		defined, the normal port 69 is used.
2537
2538		The purpose for tftpsrcp is to allow a TFTP server to
2539		blindly start the TFTP transfer using the pre-configured
2540		target IP address and UDP port. This has the effect of
2541		"punching through" the (Windows XP) firewall, allowing
2542		the remainder of the TFTP transfer to proceed normally.
2543		A better solution is to properly configure the firewall,
2544		but sometimes that is not allowed.
2545
2546- bootcount support:
2547		CONFIG_BOOTCOUNT_LIMIT
2548
2549		This enables the bootcounter support, see:
2550		http://www.denx.de/wiki/DULG/UBootBootCountLimit
2551
2552		CONFIG_AT91SAM9XE
2553		enable special bootcounter support on at91sam9xe based boards.
2554		CONFIG_SOC_DA8XX
2555		enable special bootcounter support on da850 based boards.
2556		CONFIG_BOOTCOUNT_RAM
2557		enable support for the bootcounter in RAM
2558		CONFIG_BOOTCOUNT_I2C
2559		enable support for the bootcounter on an i2c (like RTC) device.
2560			CONFIG_SYS_I2C_RTC_ADDR = i2c chip address
2561			CONFIG_SYS_BOOTCOUNT_ADDR = i2c addr which is used for
2562						    the bootcounter.
2563			CONFIG_BOOTCOUNT_ALEN = address len
2564
2565- Show boot progress:
2566		CONFIG_SHOW_BOOT_PROGRESS
2567
2568		Defining this option allows to add some board-
2569		specific code (calling a user-provided function
2570		"show_boot_progress(int)") that enables you to show
2571		the system's boot progress on some display (for
2572		example, some LED's) on your board. At the moment,
2573		the following checkpoints are implemented:
2574
2575
2576Legacy uImage format:
2577
2578  Arg	Where			When
2579    1	common/cmd_bootm.c	before attempting to boot an image
2580   -1	common/cmd_bootm.c	Image header has bad	 magic number
2581    2	common/cmd_bootm.c	Image header has correct magic number
2582   -2	common/cmd_bootm.c	Image header has bad	 checksum
2583    3	common/cmd_bootm.c	Image header has correct checksum
2584   -3	common/cmd_bootm.c	Image data   has bad	 checksum
2585    4	common/cmd_bootm.c	Image data   has correct checksum
2586   -4	common/cmd_bootm.c	Image is for unsupported architecture
2587    5	common/cmd_bootm.c	Architecture check OK
2588   -5	common/cmd_bootm.c	Wrong Image Type (not kernel, multi)
2589    6	common/cmd_bootm.c	Image Type check OK
2590   -6	common/cmd_bootm.c	gunzip uncompression error
2591   -7	common/cmd_bootm.c	Unimplemented compression type
2592    7	common/cmd_bootm.c	Uncompression OK
2593    8	common/cmd_bootm.c	No uncompress/copy overwrite error
2594   -9	common/cmd_bootm.c	Unsupported OS (not Linux, BSD, VxWorks, QNX)
2595
2596    9	common/image.c		Start initial ramdisk verification
2597  -10	common/image.c		Ramdisk header has bad	   magic number
2598  -11	common/image.c		Ramdisk header has bad	   checksum
2599   10	common/image.c		Ramdisk header is OK
2600  -12	common/image.c		Ramdisk data   has bad	   checksum
2601   11	common/image.c		Ramdisk data   has correct checksum
2602   12	common/image.c		Ramdisk verification complete, start loading
2603  -13	common/image.c		Wrong Image Type (not PPC Linux ramdisk)
2604   13	common/image.c		Start multifile image verification
2605   14	common/image.c		No initial ramdisk, no multifile, continue.
2606
2607   15	arch/<arch>/lib/bootm.c All preparation done, transferring control to OS
2608
2609  -30	arch/powerpc/lib/board.c	Fatal error, hang the system
2610  -31	post/post.c		POST test failed, detected by post_output_backlog()
2611  -32	post/post.c		POST test failed, detected by post_run_single()
2612
2613   34	common/cmd_doc.c	before loading a Image from a DOC device
2614  -35	common/cmd_doc.c	Bad usage of "doc" command
2615   35	common/cmd_doc.c	correct usage of "doc" command
2616  -36	common/cmd_doc.c	No boot device
2617   36	common/cmd_doc.c	correct boot device
2618  -37	common/cmd_doc.c	Unknown Chip ID on boot device
2619   37	common/cmd_doc.c	correct chip ID found, device available
2620  -38	common/cmd_doc.c	Read Error on boot device
2621   38	common/cmd_doc.c	reading Image header from DOC device OK
2622  -39	common/cmd_doc.c	Image header has bad magic number
2623   39	common/cmd_doc.c	Image header has correct magic number
2624  -40	common/cmd_doc.c	Error reading Image from DOC device
2625   40	common/cmd_doc.c	Image header has correct magic number
2626   41	common/cmd_ide.c	before loading a Image from a IDE device
2627  -42	common/cmd_ide.c	Bad usage of "ide" command
2628   42	common/cmd_ide.c	correct usage of "ide" command
2629  -43	common/cmd_ide.c	No boot device
2630   43	common/cmd_ide.c	boot device found
2631  -44	common/cmd_ide.c	Device not available
2632   44	common/cmd_ide.c	Device available
2633  -45	common/cmd_ide.c	wrong partition selected
2634   45	common/cmd_ide.c	partition selected
2635  -46	common/cmd_ide.c	Unknown partition table
2636   46	common/cmd_ide.c	valid partition table found
2637  -47	common/cmd_ide.c	Invalid partition type
2638   47	common/cmd_ide.c	correct partition type
2639  -48	common/cmd_ide.c	Error reading Image Header on boot device
2640   48	common/cmd_ide.c	reading Image Header from IDE device OK
2641  -49	common/cmd_ide.c	Image header has bad magic number
2642   49	common/cmd_ide.c	Image header has correct magic number
2643  -50	common/cmd_ide.c	Image header has bad	 checksum
2644   50	common/cmd_ide.c	Image header has correct checksum
2645  -51	common/cmd_ide.c	Error reading Image from IDE device
2646   51	common/cmd_ide.c	reading Image from IDE device OK
2647   52	common/cmd_nand.c	before loading a Image from a NAND device
2648  -53	common/cmd_nand.c	Bad usage of "nand" command
2649   53	common/cmd_nand.c	correct usage of "nand" command
2650  -54	common/cmd_nand.c	No boot device
2651   54	common/cmd_nand.c	boot device found
2652  -55	common/cmd_nand.c	Unknown Chip ID on boot device
2653   55	common/cmd_nand.c	correct chip ID found, device available
2654  -56	common/cmd_nand.c	Error reading Image Header on boot device
2655   56	common/cmd_nand.c	reading Image Header from NAND device OK
2656  -57	common/cmd_nand.c	Image header has bad magic number
2657   57	common/cmd_nand.c	Image header has correct magic number
2658  -58	common/cmd_nand.c	Error reading Image from NAND device
2659   58	common/cmd_nand.c	reading Image from NAND device OK
2660
2661  -60	common/env_common.c	Environment has a bad CRC, using default
2662
2663   64	net/eth.c		starting with Ethernet configuration.
2664  -64	net/eth.c		no Ethernet found.
2665   65	net/eth.c		Ethernet found.
2666
2667  -80	common/cmd_net.c	usage wrong
2668   80	common/cmd_net.c	before calling net_loop()
2669  -81	common/cmd_net.c	some error in net_loop() occurred
2670   81	common/cmd_net.c	net_loop() back without error
2671  -82	common/cmd_net.c	size == 0 (File with size 0 loaded)
2672   82	common/cmd_net.c	trying automatic boot
2673   83	common/cmd_net.c	running "source" command
2674  -83	common/cmd_net.c	some error in automatic boot or "source" command
2675   84	common/cmd_net.c	end without errors
2676
2677FIT uImage format:
2678
2679  Arg	Where			When
2680  100	common/cmd_bootm.c	Kernel FIT Image has correct format
2681 -100	common/cmd_bootm.c	Kernel FIT Image has incorrect format
2682  101	common/cmd_bootm.c	No Kernel subimage unit name, using configuration
2683 -101	common/cmd_bootm.c	Can't get configuration for kernel subimage
2684  102	common/cmd_bootm.c	Kernel unit name specified
2685 -103	common/cmd_bootm.c	Can't get kernel subimage node offset
2686  103	common/cmd_bootm.c	Found configuration node
2687  104	common/cmd_bootm.c	Got kernel subimage node offset
2688 -104	common/cmd_bootm.c	Kernel subimage hash verification failed
2689  105	common/cmd_bootm.c	Kernel subimage hash verification OK
2690 -105	common/cmd_bootm.c	Kernel subimage is for unsupported architecture
2691  106	common/cmd_bootm.c	Architecture check OK
2692 -106	common/cmd_bootm.c	Kernel subimage has wrong type
2693  107	common/cmd_bootm.c	Kernel subimage type OK
2694 -107	common/cmd_bootm.c	Can't get kernel subimage data/size
2695  108	common/cmd_bootm.c	Got kernel subimage data/size
2696 -108	common/cmd_bootm.c	Wrong image type (not legacy, FIT)
2697 -109	common/cmd_bootm.c	Can't get kernel subimage type
2698 -110	common/cmd_bootm.c	Can't get kernel subimage comp
2699 -111	common/cmd_bootm.c	Can't get kernel subimage os
2700 -112	common/cmd_bootm.c	Can't get kernel subimage load address
2701 -113	common/cmd_bootm.c	Image uncompress/copy overwrite error
2702
2703  120	common/image.c		Start initial ramdisk verification
2704 -120	common/image.c		Ramdisk FIT image has incorrect format
2705  121	common/image.c		Ramdisk FIT image has correct format
2706  122	common/image.c		No ramdisk subimage unit name, using configuration
2707 -122	common/image.c		Can't get configuration for ramdisk subimage
2708  123	common/image.c		Ramdisk unit name specified
2709 -124	common/image.c		Can't get ramdisk subimage node offset
2710  125	common/image.c		Got ramdisk subimage node offset
2711 -125	common/image.c		Ramdisk subimage hash verification failed
2712  126	common/image.c		Ramdisk subimage hash verification OK
2713 -126	common/image.c		Ramdisk subimage for unsupported architecture
2714  127	common/image.c		Architecture check OK
2715 -127	common/image.c		Can't get ramdisk subimage data/size
2716  128	common/image.c		Got ramdisk subimage data/size
2717  129	common/image.c		Can't get ramdisk load address
2718 -129	common/image.c		Got ramdisk load address
2719
2720 -130	common/cmd_doc.c	Incorrect FIT image format
2721  131	common/cmd_doc.c	FIT image format OK
2722
2723 -140	common/cmd_ide.c	Incorrect FIT image format
2724  141	common/cmd_ide.c	FIT image format OK
2725
2726 -150	common/cmd_nand.c	Incorrect FIT image format
2727  151	common/cmd_nand.c	FIT image format OK
2728
2729- legacy image format:
2730		CONFIG_IMAGE_FORMAT_LEGACY
2731		enables the legacy image format support in U-Boot.
2732
2733		Default:
2734		enabled if CONFIG_FIT_SIGNATURE is not defined.
2735
2736		CONFIG_DISABLE_IMAGE_LEGACY
2737		disable the legacy image format
2738
2739		This define is introduced, as the legacy image format is
2740		enabled per default for backward compatibility.
2741
2742- Standalone program support:
2743		CONFIG_STANDALONE_LOAD_ADDR
2744
2745		This option defines a board specific value for the
2746		address where standalone program gets loaded, thus
2747		overwriting the architecture dependent default
2748		settings.
2749
2750- Frame Buffer Address:
2751		CONFIG_FB_ADDR
2752
2753		Define CONFIG_FB_ADDR if you want to use specific
2754		address for frame buffer.  This is typically the case
2755		when using a graphics controller has separate video
2756		memory.  U-Boot will then place the frame buffer at
2757		the given address instead of dynamically reserving it
2758		in system RAM by calling lcd_setmem(), which grabs
2759		the memory for the frame buffer depending on the
2760		configured panel size.
2761
2762		Please see board_init_f function.
2763
2764- Automatic software updates via TFTP server
2765		CONFIG_UPDATE_TFTP
2766		CONFIG_UPDATE_TFTP_CNT_MAX
2767		CONFIG_UPDATE_TFTP_MSEC_MAX
2768
2769		These options enable and control the auto-update feature;
2770		for a more detailed description refer to doc/README.update.
2771
2772- MTD Support (mtdparts command, UBI support)
2773		CONFIG_MTD_DEVICE
2774
2775		Adds the MTD device infrastructure from the Linux kernel.
2776		Needed for mtdparts command support.
2777
2778		CONFIG_MTD_PARTITIONS
2779
2780		Adds the MTD partitioning infrastructure from the Linux
2781		kernel. Needed for UBI support.
2782
2783- UBI support
2784		CONFIG_UBI_SILENCE_MSG
2785
2786		Make the verbose messages from UBI stop printing.  This leaves
2787		warnings and errors enabled.
2788
2789
2790		CONFIG_MTD_UBI_WL_THRESHOLD
2791		This parameter defines the maximum difference between the highest
2792		erase counter value and the lowest erase counter value of eraseblocks
2793		of UBI devices. When this threshold is exceeded, UBI starts performing
2794		wear leveling by means of moving data from eraseblock with low erase
2795		counter to eraseblocks with high erase counter.
2796
2797		The default value should be OK for SLC NAND flashes, NOR flashes and
2798		other flashes which have eraseblock life-cycle 100000 or more.
2799		However, in case of MLC NAND flashes which typically have eraseblock
2800		life-cycle less than 10000, the threshold should be lessened (e.g.,
2801		to 128 or 256, although it does not have to be power of 2).
2802
2803		default: 4096
2804
2805		CONFIG_MTD_UBI_BEB_LIMIT
2806		This option specifies the maximum bad physical eraseblocks UBI
2807		expects on the MTD device (per 1024 eraseblocks). If the
2808		underlying flash does not admit of bad eraseblocks (e.g. NOR
2809		flash), this value is ignored.
2810
2811		NAND datasheets often specify the minimum and maximum NVM
2812		(Number of Valid Blocks) for the flashes' endurance lifetime.
2813		The maximum expected bad eraseblocks per 1024 eraseblocks
2814		then can be calculated as "1024 * (1 - MinNVB / MaxNVB)",
2815		which gives 20 for most NANDs (MaxNVB is basically the total
2816		count of eraseblocks on the chip).
2817
2818		To put it differently, if this value is 20, UBI will try to
2819		reserve about 1.9% of physical eraseblocks for bad blocks
2820		handling. And that will be 1.9% of eraseblocks on the entire
2821		NAND chip, not just the MTD partition UBI attaches. This means
2822		that if you have, say, a NAND flash chip admits maximum 40 bad
2823		eraseblocks, and it is split on two MTD partitions of the same
2824		size, UBI will reserve 40 eraseblocks when attaching a
2825		partition.
2826
2827		default: 20
2828
2829		CONFIG_MTD_UBI_FASTMAP
2830		Fastmap is a mechanism which allows attaching an UBI device
2831		in nearly constant time. Instead of scanning the whole MTD device it
2832		only has to locate a checkpoint (called fastmap) on the device.
2833		The on-flash fastmap contains all information needed to attach
2834		the device. Using fastmap makes only sense on large devices where
2835		attaching by scanning takes long. UBI will not automatically install
2836		a fastmap on old images, but you can set the UBI parameter
2837		CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT to 1 if you want so. Please note
2838		that fastmap-enabled images are still usable with UBI implementations
2839		without	fastmap support. On typical flash devices the whole fastmap
2840		fits into one PEB. UBI will reserve PEBs to hold two fastmaps.
2841
2842		CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT
2843		Set this parameter to enable fastmap automatically on images
2844		without a fastmap.
2845		default: 0
2846
2847		CONFIG_MTD_UBI_FM_DEBUG
2848		Enable UBI fastmap debug
2849		default: 0
2850
2851- UBIFS support
2852		CONFIG_UBIFS_SILENCE_MSG
2853
2854		Make the verbose messages from UBIFS stop printing.  This leaves
2855		warnings and errors enabled.
2856
2857- SPL framework
2858		CONFIG_SPL
2859		Enable building of SPL globally.
2860
2861		CONFIG_SPL_LDSCRIPT
2862		LDSCRIPT for linking the SPL binary.
2863
2864		CONFIG_SPL_MAX_FOOTPRINT
2865		Maximum size in memory allocated to the SPL, BSS included.
2866		When defined, the linker checks that the actual memory
2867		used by SPL from _start to __bss_end does not exceed it.
2868		CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE
2869		must not be both defined at the same time.
2870
2871		CONFIG_SPL_MAX_SIZE
2872		Maximum size of the SPL image (text, data, rodata, and
2873		linker lists sections), BSS excluded.
2874		When defined, the linker checks that the actual size does
2875		not exceed it.
2876
2877		CONFIG_SPL_TEXT_BASE
2878		TEXT_BASE for linking the SPL binary.
2879
2880		CONFIG_SPL_RELOC_TEXT_BASE
2881		Address to relocate to.  If unspecified, this is equal to
2882		CONFIG_SPL_TEXT_BASE (i.e. no relocation is done).
2883
2884		CONFIG_SPL_BSS_START_ADDR
2885		Link address for the BSS within the SPL binary.
2886
2887		CONFIG_SPL_BSS_MAX_SIZE
2888		Maximum size in memory allocated to the SPL BSS.
2889		When defined, the linker checks that the actual memory used
2890		by SPL from __bss_start to __bss_end does not exceed it.
2891		CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE
2892		must not be both defined at the same time.
2893
2894		CONFIG_SPL_STACK
2895		Adress of the start of the stack SPL will use
2896
2897		CONFIG_SPL_PANIC_ON_RAW_IMAGE
2898		When defined, SPL will panic() if the image it has
2899		loaded does not have a signature.
2900		Defining this is useful when code which loads images
2901		in SPL cannot guarantee that absolutely all read errors
2902		will be caught.
2903		An example is the LPC32XX MLC NAND driver, which will
2904		consider that a completely unreadable NAND block is bad,
2905		and thus should be skipped silently.
2906
2907		CONFIG_SPL_RELOC_STACK
2908		Adress of the start of the stack SPL will use after
2909		relocation.  If unspecified, this is equal to
2910		CONFIG_SPL_STACK.
2911
2912		CONFIG_SYS_SPL_MALLOC_START
2913		Starting address of the malloc pool used in SPL.
2914		When this option is set the full malloc is used in SPL and
2915		it is set up by spl_init() and before that, the simple malloc()
2916		can be used if CONFIG_SYS_MALLOC_F is defined.
2917
2918		CONFIG_SYS_SPL_MALLOC_SIZE
2919		The size of the malloc pool used in SPL.
2920
2921		CONFIG_SPL_FRAMEWORK
2922		Enable the SPL framework under common/.  This framework
2923		supports MMC, NAND and YMODEM loading of U-Boot and NAND
2924		NAND loading of the Linux Kernel.
2925
2926		CONFIG_SPL_OS_BOOT
2927		Enable booting directly to an OS from SPL.
2928		See also: doc/README.falcon
2929
2930		CONFIG_SPL_DISPLAY_PRINT
2931		For ARM, enable an optional function to print more information
2932		about the running system.
2933
2934		CONFIG_SPL_INIT_MINIMAL
2935		Arch init code should be built for a very small image
2936
2937		CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_PARTITION
2938		Partition on the MMC to load U-Boot from when the MMC is being
2939		used in raw mode
2940
2941		CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR
2942		Sector to load kernel uImage from when MMC is being
2943		used in raw mode (for Falcon mode)
2944
2945		CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR,
2946		CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTORS
2947		Sector and number of sectors to load kernel argument
2948		parameters from when MMC is being used in raw mode
2949		(for falcon mode)
2950
2951		CONFIG_SYS_MMCSD_FS_BOOT_PARTITION
2952		Partition on the MMC to load U-Boot from when the MMC is being
2953		used in fs mode
2954
2955		CONFIG_SPL_FS_LOAD_PAYLOAD_NAME
2956		Filename to read to load U-Boot when reading from filesystem
2957
2958		CONFIG_SPL_FS_LOAD_KERNEL_NAME
2959		Filename to read to load kernel uImage when reading
2960		from filesystem (for Falcon mode)
2961
2962		CONFIG_SPL_FS_LOAD_ARGS_NAME
2963		Filename to read to load kernel argument parameters
2964		when reading from filesystem (for Falcon mode)
2965
2966		CONFIG_SPL_MPC83XX_WAIT_FOR_NAND
2967		Set this for NAND SPL on PPC mpc83xx targets, so that
2968		start.S waits for the rest of the SPL to load before
2969		continuing (the hardware starts execution after just
2970		loading the first page rather than the full 4K).
2971
2972		CONFIG_SPL_SKIP_RELOCATE
2973		Avoid SPL relocation
2974
2975		CONFIG_SPL_NAND_BASE
2976		Include nand_base.c in the SPL.  Requires
2977		CONFIG_SPL_NAND_DRIVERS.
2978
2979		CONFIG_SPL_NAND_DRIVERS
2980		SPL uses normal NAND drivers, not minimal drivers.
2981
2982		CONFIG_SPL_NAND_ECC
2983		Include standard software ECC in the SPL
2984
2985		CONFIG_SPL_NAND_SIMPLE
2986		Support for NAND boot using simple NAND drivers that
2987		expose the cmd_ctrl() interface.
2988
2989		CONFIG_SPL_UBI
2990		Support for a lightweight UBI (fastmap) scanner and
2991		loader
2992
2993		CONFIG_SPL_NAND_RAW_ONLY
2994		Support to boot only raw u-boot.bin images. Use this only
2995		if you need to save space.
2996
2997		CONFIG_SPL_COMMON_INIT_DDR
2998		Set for common ddr init with serial presence detect in
2999		SPL binary.
3000
3001		CONFIG_SYS_NAND_5_ADDR_CYCLE, CONFIG_SYS_NAND_PAGE_COUNT,
3002		CONFIG_SYS_NAND_PAGE_SIZE, CONFIG_SYS_NAND_OOBSIZE,
3003		CONFIG_SYS_NAND_BLOCK_SIZE, CONFIG_SYS_NAND_BAD_BLOCK_POS,
3004		CONFIG_SYS_NAND_ECCPOS, CONFIG_SYS_NAND_ECCSIZE,
3005		CONFIG_SYS_NAND_ECCBYTES
3006		Defines the size and behavior of the NAND that SPL uses
3007		to read U-Boot
3008
3009		CONFIG_SPL_NAND_BOOT
3010		Add support NAND boot
3011
3012		CONFIG_SYS_NAND_U_BOOT_OFFS
3013		Location in NAND to read U-Boot from
3014
3015		CONFIG_SYS_NAND_U_BOOT_DST
3016		Location in memory to load U-Boot to
3017
3018		CONFIG_SYS_NAND_U_BOOT_SIZE
3019		Size of image to load
3020
3021		CONFIG_SYS_NAND_U_BOOT_START
3022		Entry point in loaded image to jump to
3023
3024		CONFIG_SYS_NAND_HW_ECC_OOBFIRST
3025		Define this if you need to first read the OOB and then the
3026		data. This is used, for example, on davinci platforms.
3027
3028		CONFIG_SPL_OMAP3_ID_NAND
3029		Support for an OMAP3-specific set of functions to return the
3030		ID and MFR of the first attached NAND chip, if present.
3031
3032		CONFIG_SPL_RAM_DEVICE
3033		Support for running image already present in ram, in SPL binary
3034
3035		CONFIG_SPL_PAD_TO
3036		Image offset to which the SPL should be padded before appending
3037		the SPL payload. By default, this is defined as
3038		CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.
3039		CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL
3040		payload without any padding, or >= CONFIG_SPL_MAX_SIZE.
3041
3042		CONFIG_SPL_TARGET
3043		Final target image containing SPL and payload.  Some SPLs
3044		use an arch-specific makefile fragment instead, for
3045		example if more than one image needs to be produced.
3046
3047		CONFIG_FIT_SPL_PRINT
3048		Printing information about a FIT image adds quite a bit of
3049		code to SPL. So this is normally disabled in SPL. Use this
3050		option to re-enable it. This will affect the output of the
3051		bootm command when booting a FIT image.
3052
3053- TPL framework
3054		CONFIG_TPL
3055		Enable building of TPL globally.
3056
3057		CONFIG_TPL_PAD_TO
3058		Image offset to which the TPL should be padded before appending
3059		the TPL payload. By default, this is defined as
3060		CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.
3061		CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL
3062		payload without any padding, or >= CONFIG_SPL_MAX_SIZE.
3063
3064- Interrupt support (PPC):
3065
3066		There are common interrupt_init() and timer_interrupt()
3067		for all PPC archs. interrupt_init() calls interrupt_init_cpu()
3068		for CPU specific initialization. interrupt_init_cpu()
3069		should set decrementer_count to appropriate value. If
3070		CPU resets decrementer automatically after interrupt
3071		(ppc4xx) it should set decrementer_count to zero.
3072		timer_interrupt() calls timer_interrupt_cpu() for CPU
3073		specific handling. If board has watchdog / status_led
3074		/ other_activity_monitor it works automatically from
3075		general timer_interrupt().
3076
3077
3078Board initialization settings:
3079------------------------------
3080
3081During Initialization u-boot calls a number of board specific functions
3082to allow the preparation of board specific prerequisites, e.g. pin setup
3083before drivers are initialized. To enable these callbacks the
3084following configuration macros have to be defined. Currently this is
3085architecture specific, so please check arch/your_architecture/lib/board.c
3086typically in board_init_f() and board_init_r().
3087
3088- CONFIG_BOARD_EARLY_INIT_F: Call board_early_init_f()
3089- CONFIG_BOARD_EARLY_INIT_R: Call board_early_init_r()
3090- CONFIG_BOARD_LATE_INIT: Call board_late_init()
3091- CONFIG_BOARD_POSTCLK_INIT: Call board_postclk_init()
3092
3093Configuration Settings:
3094-----------------------
3095
3096- CONFIG_SYS_SUPPORT_64BIT_DATA: Defined automatically if compiled as 64-bit.
3097		Optionally it can be defined to support 64-bit memory commands.
3098
3099- CONFIG_SYS_LONGHELP: Defined when you want long help messages included;
3100		undefine this when you're short of memory.
3101
3102- CONFIG_SYS_HELP_CMD_WIDTH: Defined when you want to override the default
3103		width of the commands listed in the 'help' command output.
3104
3105- CONFIG_SYS_PROMPT:	This is what U-Boot prints on the console to
3106		prompt for user input.
3107
3108- CONFIG_SYS_CBSIZE:	Buffer size for input from the Console
3109
3110- CONFIG_SYS_PBSIZE:	Buffer size for Console output
3111
3112- CONFIG_SYS_MAXARGS:	max. Number of arguments accepted for monitor commands
3113
3114- CONFIG_SYS_BARGSIZE: Buffer size for Boot Arguments which are passed to
3115		the application (usually a Linux kernel) when it is
3116		booted
3117
3118- CONFIG_SYS_BAUDRATE_TABLE:
3119		List of legal baudrate settings for this board.
3120
3121- CONFIG_SYS_MEMTEST_START, CONFIG_SYS_MEMTEST_END:
3122		Begin and End addresses of the area used by the
3123		simple memory test.
3124
3125- CONFIG_SYS_ALT_MEMTEST:
3126		Enable an alternate, more extensive memory test.
3127
3128- CONFIG_SYS_MEMTEST_SCRATCH:
3129		Scratch address used by the alternate memory test
3130		You only need to set this if address zero isn't writeable
3131
3132- CONFIG_SYS_MEM_RESERVE_SECURE
3133		Only implemented for ARMv8 for now.
3134		If defined, the size of CONFIG_SYS_MEM_RESERVE_SECURE memory
3135		is substracted from total RAM and won't be reported to OS.
3136		This memory can be used as secure memory. A variable
3137		gd->arch.secure_ram is used to track the location. In systems
3138		the RAM base is not zero, or RAM is divided into banks,
3139		this variable needs to be recalcuated to get the address.
3140
3141- CONFIG_SYS_MEM_TOP_HIDE:
3142		If CONFIG_SYS_MEM_TOP_HIDE is defined in the board config header,
3143		this specified memory area will get subtracted from the top
3144		(end) of RAM and won't get "touched" at all by U-Boot. By
3145		fixing up gd->ram_size the Linux kernel should gets passed
3146		the now "corrected" memory size and won't touch it either.
3147		This should work for arch/ppc and arch/powerpc. Only Linux
3148		board ports in arch/powerpc with bootwrapper support that
3149		recalculate the memory size from the SDRAM controller setup
3150		will have to get fixed in Linux additionally.
3151
3152		This option can be used as a workaround for the 440EPx/GRx
3153		CHIP 11 errata where the last 256 bytes in SDRAM shouldn't
3154		be touched.
3155
3156		WARNING: Please make sure that this value is a multiple of
3157		the Linux page size (normally 4k). If this is not the case,
3158		then the end address of the Linux memory will be located at a
3159		non page size aligned address and this could cause major
3160		problems.
3161
3162- CONFIG_SYS_LOADS_BAUD_CHANGE:
3163		Enable temporary baudrate change while serial download
3164
3165- CONFIG_SYS_SDRAM_BASE:
3166		Physical start address of SDRAM. _Must_ be 0 here.
3167
3168- CONFIG_SYS_FLASH_BASE:
3169		Physical start address of Flash memory.
3170
3171- CONFIG_SYS_MONITOR_BASE:
3172		Physical start address of boot monitor code (set by
3173		make config files to be same as the text base address
3174		(CONFIG_SYS_TEXT_BASE) used when linking) - same as
3175		CONFIG_SYS_FLASH_BASE when booting from flash.
3176
3177- CONFIG_SYS_MONITOR_LEN:
3178		Size of memory reserved for monitor code, used to
3179		determine _at_compile_time_ (!) if the environment is
3180		embedded within the U-Boot image, or in a separate
3181		flash sector.
3182
3183- CONFIG_SYS_MALLOC_LEN:
3184		Size of DRAM reserved for malloc() use.
3185
3186- CONFIG_SYS_MALLOC_F_LEN
3187		Size of the malloc() pool for use before relocation. If
3188		this is defined, then a very simple malloc() implementation
3189		will become available before relocation. The address is just
3190		below the global data, and the stack is moved down to make
3191		space.
3192
3193		This feature allocates regions with increasing addresses
3194		within the region. calloc() is supported, but realloc()
3195		is not available. free() is supported but does nothing.
3196		The memory will be freed (or in fact just forgotten) when
3197		U-Boot relocates itself.
3198
3199- CONFIG_SYS_MALLOC_SIMPLE
3200		Provides a simple and small malloc() and calloc() for those
3201		boards which do not use the full malloc in SPL (which is
3202		enabled with CONFIG_SYS_SPL_MALLOC_START).
3203
3204- CONFIG_SYS_NONCACHED_MEMORY:
3205		Size of non-cached memory area. This area of memory will be
3206		typically located right below the malloc() area and mapped
3207		uncached in the MMU. This is useful for drivers that would
3208		otherwise require a lot of explicit cache maintenance. For
3209		some drivers it's also impossible to properly maintain the
3210		cache. For example if the regions that need to be flushed
3211		are not a multiple of the cache-line size, *and* padding
3212		cannot be allocated between the regions to align them (i.e.
3213		if the HW requires a contiguous array of regions, and the
3214		size of each region is not cache-aligned), then a flush of
3215		one region may result in overwriting data that hardware has
3216		written to another region in the same cache-line. This can
3217		happen for example in network drivers where descriptors for
3218		buffers are typically smaller than the CPU cache-line (e.g.
3219		16 bytes vs. 32 or 64 bytes).
3220
3221		Non-cached memory is only supported on 32-bit ARM at present.
3222
3223- CONFIG_SYS_BOOTM_LEN:
3224		Normally compressed uImages are limited to an
3225		uncompressed size of 8 MBytes. If this is not enough,
3226		you can define CONFIG_SYS_BOOTM_LEN in your board config file
3227		to adjust this setting to your needs.
3228
3229- CONFIG_SYS_BOOTMAPSZ:
3230		Maximum size of memory mapped by the startup code of
3231		the Linux kernel; all data that must be processed by
3232		the Linux kernel (bd_info, boot arguments, FDT blob if
3233		used) must be put below this limit, unless "bootm_low"
3234		environment variable is defined and non-zero. In such case
3235		all data for the Linux kernel must be between "bootm_low"
3236		and "bootm_low" + CONFIG_SYS_BOOTMAPSZ.	 The environment
3237		variable "bootm_mapsize" will override the value of
3238		CONFIG_SYS_BOOTMAPSZ.  If CONFIG_SYS_BOOTMAPSZ is undefined,
3239		then the value in "bootm_size" will be used instead.
3240
3241- CONFIG_SYS_BOOT_RAMDISK_HIGH:
3242		Enable initrd_high functionality.  If defined then the
3243		initrd_high feature is enabled and the bootm ramdisk subcommand
3244		is enabled.
3245
3246- CONFIG_SYS_BOOT_GET_CMDLINE:
3247		Enables allocating and saving kernel cmdline in space between
3248		"bootm_low" and "bootm_low" + BOOTMAPSZ.
3249
3250- CONFIG_SYS_BOOT_GET_KBD:
3251		Enables allocating and saving a kernel copy of the bd_info in
3252		space between "bootm_low" and "bootm_low" + BOOTMAPSZ.
3253
3254- CONFIG_SYS_MAX_FLASH_BANKS:
3255		Max number of Flash memory banks
3256
3257- CONFIG_SYS_MAX_FLASH_SECT:
3258		Max number of sectors on a Flash chip
3259
3260- CONFIG_SYS_FLASH_ERASE_TOUT:
3261		Timeout for Flash erase operations (in ms)
3262
3263- CONFIG_SYS_FLASH_WRITE_TOUT:
3264		Timeout for Flash write operations (in ms)
3265
3266- CONFIG_SYS_FLASH_LOCK_TOUT
3267		Timeout for Flash set sector lock bit operation (in ms)
3268
3269- CONFIG_SYS_FLASH_UNLOCK_TOUT
3270		Timeout for Flash clear lock bits operation (in ms)
3271
3272- CONFIG_SYS_FLASH_PROTECTION
3273		If defined, hardware flash sectors protection is used
3274		instead of U-Boot software protection.
3275
3276- CONFIG_SYS_DIRECT_FLASH_TFTP:
3277
3278		Enable TFTP transfers directly to flash memory;
3279		without this option such a download has to be
3280		performed in two steps: (1) download to RAM, and (2)
3281		copy from RAM to flash.
3282
3283		The two-step approach is usually more reliable, since
3284		you can check if the download worked before you erase
3285		the flash, but in some situations (when system RAM is
3286		too limited to allow for a temporary copy of the
3287		downloaded image) this option may be very useful.
3288
3289- CONFIG_SYS_FLASH_CFI:
3290		Define if the flash driver uses extra elements in the
3291		common flash structure for storing flash geometry.
3292
3293- CONFIG_FLASH_CFI_DRIVER
3294		This option also enables the building of the cfi_flash driver
3295		in the drivers directory
3296
3297- CONFIG_FLASH_CFI_MTD
3298		This option enables the building of the cfi_mtd driver
3299		in the drivers directory. The driver exports CFI flash
3300		to the MTD layer.
3301
3302- CONFIG_SYS_FLASH_USE_BUFFER_WRITE
3303		Use buffered writes to flash.
3304
3305- CONFIG_FLASH_SPANSION_S29WS_N
3306		s29ws-n MirrorBit flash has non-standard addresses for buffered
3307		write commands.
3308
3309- CONFIG_SYS_FLASH_QUIET_TEST
3310		If this option is defined, the common CFI flash doesn't
3311		print it's warning upon not recognized FLASH banks. This
3312		is useful, if some of the configured banks are only
3313		optionally available.
3314
3315- CONFIG_FLASH_SHOW_PROGRESS
3316		If defined (must be an integer), print out countdown
3317		digits and dots.  Recommended value: 45 (9..1) for 80
3318		column displays, 15 (3..1) for 40 column displays.
3319
3320- CONFIG_FLASH_VERIFY
3321		If defined, the content of the flash (destination) is compared
3322		against the source after the write operation. An error message
3323		will be printed when the contents are not identical.
3324		Please note that this option is useless in nearly all cases,
3325		since such flash programming errors usually are detected earlier
3326		while unprotecting/erasing/programming. Please only enable
3327		this option if you really know what you are doing.
3328
3329- CONFIG_SYS_RX_ETH_BUFFER:
3330		Defines the number of Ethernet receive buffers. On some
3331		Ethernet controllers it is recommended to set this value
3332		to 8 or even higher (EEPRO100 or 405 EMAC), since all
3333		buffers can be full shortly after enabling the interface
3334		on high Ethernet traffic.
3335		Defaults to 4 if not defined.
3336
3337- CONFIG_ENV_MAX_ENTRIES
3338
3339	Maximum number of entries in the hash table that is used
3340	internally to store the environment settings. The default
3341	setting is supposed to be generous and should work in most
3342	cases. This setting can be used to tune behaviour; see
3343	lib/hashtable.c for details.
3344
3345- CONFIG_ENV_FLAGS_LIST_DEFAULT
3346- CONFIG_ENV_FLAGS_LIST_STATIC
3347	Enable validation of the values given to environment variables when
3348	calling env set.  Variables can be restricted to only decimal,
3349	hexadecimal, or boolean.  If CONFIG_CMD_NET is also defined,
3350	the variables can also be restricted to IP address or MAC address.
3351
3352	The format of the list is:
3353		type_attribute = [s|d|x|b|i|m]
3354		access_attribute = [a|r|o|c]
3355		attributes = type_attribute[access_attribute]
3356		entry = variable_name[:attributes]
3357		list = entry[,list]
3358
3359	The type attributes are:
3360		s - String (default)
3361		d - Decimal
3362		x - Hexadecimal
3363		b - Boolean ([1yYtT|0nNfF])
3364		i - IP address
3365		m - MAC address
3366
3367	The access attributes are:
3368		a - Any (default)
3369		r - Read-only
3370		o - Write-once
3371		c - Change-default
3372
3373	- CONFIG_ENV_FLAGS_LIST_DEFAULT
3374		Define this to a list (string) to define the ".flags"
3375		environment variable in the default or embedded environment.
3376
3377	- CONFIG_ENV_FLAGS_LIST_STATIC
3378		Define this to a list (string) to define validation that
3379		should be done if an entry is not found in the ".flags"
3380		environment variable.  To override a setting in the static
3381		list, simply add an entry for the same variable name to the
3382		".flags" variable.
3383
3384	If CONFIG_REGEX is defined, the variable_name above is evaluated as a
3385	regular expression. This allows multiple variables to define the same
3386	flags without explicitly listing them for each variable.
3387
3388- CONFIG_ENV_ACCESS_IGNORE_FORCE
3389	If defined, don't allow the -f switch to env set override variable
3390	access flags.
3391
3392- CONFIG_USE_STDINT
3393	If stdint.h is available with your toolchain you can define this
3394	option to enable it. You can provide option 'USE_STDINT=1' when
3395	building U-Boot to enable this.
3396
3397The following definitions that deal with the placement and management
3398of environment data (variable area); in general, we support the
3399following configurations:
3400
3401- CONFIG_BUILD_ENVCRC:
3402
3403	Builds up envcrc with the target environment so that external utils
3404	may easily extract it and embed it in final U-Boot images.
3405
3406BE CAREFUL! The first access to the environment happens quite early
3407in U-Boot initialization (when we try to get the setting of for the
3408console baudrate). You *MUST* have mapped your NVRAM area then, or
3409U-Boot will hang.
3410
3411Please note that even with NVRAM we still use a copy of the
3412environment in RAM: we could work on NVRAM directly, but we want to
3413keep settings there always unmodified except somebody uses "saveenv"
3414to save the current settings.
3415
3416BE CAREFUL! For some special cases, the local device can not use
3417"saveenv" command. For example, the local device will get the
3418environment stored in a remote NOR flash by SRIO or PCIE link,
3419but it can not erase, write this NOR flash by SRIO or PCIE interface.
3420
3421- CONFIG_NAND_ENV_DST
3422
3423	Defines address in RAM to which the nand_spl code should copy the
3424	environment. If redundant environment is used, it will be copied to
3425	CONFIG_NAND_ENV_DST + CONFIG_ENV_SIZE.
3426
3427Please note that the environment is read-only until the monitor
3428has been relocated to RAM and a RAM copy of the environment has been
3429created; also, when using EEPROM you will have to use getenv_f()
3430until then to read environment variables.
3431
3432The environment is protected by a CRC32 checksum. Before the monitor
3433is relocated into RAM, as a result of a bad CRC you will be working
3434with the compiled-in default environment - *silently*!!! [This is
3435necessary, because the first environment variable we need is the
3436"baudrate" setting for the console - if we have a bad CRC, we don't
3437have any device yet where we could complain.]
3438
3439Note: once the monitor has been relocated, then it will complain if
3440the default environment is used; a new CRC is computed as soon as you
3441use the "saveenv" command to store a valid environment.
3442
3443- CONFIG_SYS_FAULT_ECHO_LINK_DOWN:
3444		Echo the inverted Ethernet link state to the fault LED.
3445
3446		Note: If this option is active, then CONFIG_SYS_FAULT_MII_ADDR
3447		      also needs to be defined.
3448
3449- CONFIG_SYS_FAULT_MII_ADDR:
3450		MII address of the PHY to check for the Ethernet link state.
3451
3452- CONFIG_NS16550_MIN_FUNCTIONS:
3453		Define this if you desire to only have use of the NS16550_init
3454		and NS16550_putc functions for the serial driver located at
3455		drivers/serial/ns16550.c.  This option is useful for saving
3456		space for already greatly restricted images, including but not
3457		limited to NAND_SPL configurations.
3458
3459- CONFIG_DISPLAY_BOARDINFO
3460		Display information about the board that U-Boot is running on
3461		when U-Boot starts up. The board function checkboard() is called
3462		to do this.
3463
3464- CONFIG_DISPLAY_BOARDINFO_LATE
3465		Similar to the previous option, but display this information
3466		later, once stdio is running and output goes to the LCD, if
3467		present.
3468
3469- CONFIG_BOARD_SIZE_LIMIT:
3470		Maximum size of the U-Boot image. When defined, the
3471		build system checks that the actual size does not
3472		exceed it.
3473
3474Low Level (hardware related) configuration options:
3475---------------------------------------------------
3476
3477- CONFIG_SYS_CACHELINE_SIZE:
3478		Cache Line Size of the CPU.
3479
3480- CONFIG_SYS_CCSRBAR_DEFAULT:
3481		Default (power-on reset) physical address of CCSR on Freescale
3482		PowerPC SOCs.
3483
3484- CONFIG_SYS_CCSRBAR:
3485		Virtual address of CCSR.  On a 32-bit build, this is typically
3486		the same value as CONFIG_SYS_CCSRBAR_DEFAULT.
3487
3488- CONFIG_SYS_CCSRBAR_PHYS:
3489		Physical address of CCSR.  CCSR can be relocated to a new
3490		physical address, if desired.  In this case, this macro should
3491		be set to that address.	 Otherwise, it should be set to the
3492		same value as CONFIG_SYS_CCSRBAR_DEFAULT.  For example, CCSR
3493		is typically relocated on 36-bit builds.  It is recommended
3494		that this macro be defined via the _HIGH and _LOW macros:
3495
3496		#define CONFIG_SYS_CCSRBAR_PHYS ((CONFIG_SYS_CCSRBAR_PHYS_HIGH
3497			* 1ull) << 32 | CONFIG_SYS_CCSRBAR_PHYS_LOW)
3498
3499- CONFIG_SYS_CCSRBAR_PHYS_HIGH:
3500		Bits 33-36 of CONFIG_SYS_CCSRBAR_PHYS.	This value is typically
3501		either 0 (32-bit build) or 0xF (36-bit build).	This macro is
3502		used in assembly code, so it must not contain typecasts or
3503		integer size suffixes (e.g. "ULL").
3504
3505- CONFIG_SYS_CCSRBAR_PHYS_LOW:
3506		Lower 32-bits of CONFIG_SYS_CCSRBAR_PHYS.  This macro is
3507		used in assembly code, so it must not contain typecasts or
3508		integer size suffixes (e.g. "ULL").
3509
3510- CONFIG_SYS_CCSR_DO_NOT_RELOCATE:
3511		If this macro is defined, then CONFIG_SYS_CCSRBAR_PHYS will be
3512		forced to a value that ensures that CCSR is not relocated.
3513
3514- Floppy Disk Support:
3515		CONFIG_SYS_FDC_DRIVE_NUMBER
3516
3517		the default drive number (default value 0)
3518
3519		CONFIG_SYS_ISA_IO_STRIDE
3520
3521		defines the spacing between FDC chipset registers
3522		(default value 1)
3523
3524		CONFIG_SYS_ISA_IO_OFFSET
3525
3526		defines the offset of register from address. It
3527		depends on which part of the data bus is connected to
3528		the FDC chipset. (default value 0)
3529
3530		If CONFIG_SYS_ISA_IO_STRIDE CONFIG_SYS_ISA_IO_OFFSET and
3531		CONFIG_SYS_FDC_DRIVE_NUMBER are undefined, they take their
3532		default value.
3533
3534		if CONFIG_SYS_FDC_HW_INIT is defined, then the function
3535		fdc_hw_init() is called at the beginning of the FDC
3536		setup. fdc_hw_init() must be provided by the board
3537		source code. It is used to make hardware-dependent
3538		initializations.
3539
3540- CONFIG_IDE_AHB:
3541		Most IDE controllers were designed to be connected with PCI
3542		interface. Only few of them were designed for AHB interface.
3543		When software is doing ATA command and data transfer to
3544		IDE devices through IDE-AHB controller, some additional
3545		registers accessing to these kind of IDE-AHB controller
3546		is required.
3547
3548- CONFIG_SYS_IMMR:	Physical address of the Internal Memory.
3549		DO NOT CHANGE unless you know exactly what you're
3550		doing! (11-4) [MPC8xx systems only]
3551
3552- CONFIG_SYS_INIT_RAM_ADDR:
3553
3554		Start address of memory area that can be used for
3555		initial data and stack; please note that this must be
3556		writable memory that is working WITHOUT special
3557		initialization, i. e. you CANNOT use normal RAM which
3558		will become available only after programming the
3559		memory controller and running certain initialization
3560		sequences.
3561
3562		U-Boot uses the following memory types:
3563		- MPC8xx: IMMR (internal memory of the CPU)
3564
3565- CONFIG_SYS_GBL_DATA_OFFSET:
3566
3567		Offset of the initial data structure in the memory
3568		area defined by CONFIG_SYS_INIT_RAM_ADDR. Usually
3569		CONFIG_SYS_GBL_DATA_OFFSET is chosen such that the initial
3570		data is located at the end of the available space
3571		(sometimes written as (CONFIG_SYS_INIT_RAM_SIZE -
3572		GENERATED_GBL_DATA_SIZE), and the initial stack is just
3573		below that area (growing from (CONFIG_SYS_INIT_RAM_ADDR +
3574		CONFIG_SYS_GBL_DATA_OFFSET) downward.
3575
3576	Note:
3577		On the MPC824X (or other systems that use the data
3578		cache for initial memory) the address chosen for
3579		CONFIG_SYS_INIT_RAM_ADDR is basically arbitrary - it must
3580		point to an otherwise UNUSED address space between
3581		the top of RAM and the start of the PCI space.
3582
3583- CONFIG_SYS_SCCR:	System Clock and reset Control Register (15-27)
3584
3585- CONFIG_SYS_OR_TIMING_SDRAM:
3586		SDRAM timing
3587
3588- CONFIG_SYS_MAMR_PTA:
3589		periodic timer for refresh
3590
3591- FLASH_BASE0_PRELIM, FLASH_BASE1_PRELIM, CONFIG_SYS_REMAP_OR_AM,
3592  CONFIG_SYS_PRELIM_OR_AM, CONFIG_SYS_OR_TIMING_FLASH, CONFIG_SYS_OR0_REMAP,
3593  CONFIG_SYS_OR0_PRELIM, CONFIG_SYS_BR0_PRELIM, CONFIG_SYS_OR1_REMAP, CONFIG_SYS_OR1_PRELIM,
3594  CONFIG_SYS_BR1_PRELIM:
3595		Memory Controller Definitions: BR0/1 and OR0/1 (FLASH)
3596
3597- SDRAM_BASE2_PRELIM, SDRAM_BASE3_PRELIM, SDRAM_MAX_SIZE,
3598  CONFIG_SYS_OR_TIMING_SDRAM, CONFIG_SYS_OR2_PRELIM, CONFIG_SYS_BR2_PRELIM,
3599  CONFIG_SYS_OR3_PRELIM, CONFIG_SYS_BR3_PRELIM:
3600		Memory Controller Definitions: BR2/3 and OR2/3 (SDRAM)
3601
3602- CONFIG_PCI_ENUM_ONLY
3603		Only scan through and get the devices on the buses.
3604		Don't do any setup work, presumably because someone or
3605		something has already done it, and we don't need to do it
3606		a second time.	Useful for platforms that are pre-booted
3607		by coreboot or similar.
3608
3609- CONFIG_PCI_INDIRECT_BRIDGE:
3610		Enable support for indirect PCI bridges.
3611
3612- CONFIG_SYS_SRIO:
3613		Chip has SRIO or not
3614
3615- CONFIG_SRIO1:
3616		Board has SRIO 1 port available
3617
3618- CONFIG_SRIO2:
3619		Board has SRIO 2 port available
3620
3621- CONFIG_SRIO_PCIE_BOOT_MASTER
3622		Board can support master function for Boot from SRIO and PCIE
3623
3624- CONFIG_SYS_SRIOn_MEM_VIRT:
3625		Virtual Address of SRIO port 'n' memory region
3626
3627- CONFIG_SYS_SRIOn_MEM_PHYS:
3628		Physical Address of SRIO port 'n' memory region
3629
3630- CONFIG_SYS_SRIOn_MEM_SIZE:
3631		Size of SRIO port 'n' memory region
3632
3633- CONFIG_SYS_NAND_BUSWIDTH_16BIT
3634		Defined to tell the NAND controller that the NAND chip is using
3635		a 16 bit bus.
3636		Not all NAND drivers use this symbol.
3637		Example of drivers that use it:
3638		- drivers/mtd/nand/ndfc.c
3639		- drivers/mtd/nand/mxc_nand.c
3640
3641- CONFIG_SYS_NDFC_EBC0_CFG
3642		Sets the EBC0_CFG register for the NDFC. If not defined
3643		a default value will be used.
3644
3645- CONFIG_SPD_EEPROM
3646		Get DDR timing information from an I2C EEPROM. Common
3647		with pluggable memory modules such as SODIMMs
3648
3649  SPD_EEPROM_ADDRESS
3650		I2C address of the SPD EEPROM
3651
3652- CONFIG_SYS_SPD_BUS_NUM
3653		If SPD EEPROM is on an I2C bus other than the first
3654		one, specify here. Note that the value must resolve
3655		to something your driver can deal with.
3656
3657- CONFIG_SYS_DDR_RAW_TIMING
3658		Get DDR timing information from other than SPD. Common with
3659		soldered DDR chips onboard without SPD. DDR raw timing
3660		parameters are extracted from datasheet and hard-coded into
3661		header files or board specific files.
3662
3663- CONFIG_FSL_DDR_INTERACTIVE
3664		Enable interactive DDR debugging. See doc/README.fsl-ddr.
3665
3666- CONFIG_FSL_DDR_SYNC_REFRESH
3667		Enable sync of refresh for multiple controllers.
3668
3669- CONFIG_FSL_DDR_BIST
3670		Enable built-in memory test for Freescale DDR controllers.
3671
3672- CONFIG_SYS_83XX_DDR_USES_CS0
3673		Only for 83xx systems. If specified, then DDR should
3674		be configured using CS0 and CS1 instead of CS2 and CS3.
3675
3676- CONFIG_RMII
3677		Enable RMII mode for all FECs.
3678		Note that this is a global option, we can't
3679		have one FEC in standard MII mode and another in RMII mode.
3680
3681- CONFIG_CRC32_VERIFY
3682		Add a verify option to the crc32 command.
3683		The syntax is:
3684
3685		=> crc32 -v <address> <count> <crc32>
3686
3687		Where address/count indicate a memory area
3688		and crc32 is the correct crc32 which the
3689		area should have.
3690
3691- CONFIG_LOOPW
3692		Add the "loopw" memory command. This only takes effect if
3693		the memory commands are activated globally (CONFIG_CMD_MEMORY).
3694
3695- CONFIG_MX_CYCLIC
3696		Add the "mdc" and "mwc" memory commands. These are cyclic
3697		"md/mw" commands.
3698		Examples:
3699
3700		=> mdc.b 10 4 500
3701		This command will print 4 bytes (10,11,12,13) each 500 ms.
3702
3703		=> mwc.l 100 12345678 10
3704		This command will write 12345678 to address 100 all 10 ms.
3705
3706		This only takes effect if the memory commands are activated
3707		globally (CONFIG_CMD_MEMORY).
3708
3709- CONFIG_SKIP_LOWLEVEL_INIT
3710		[ARM, NDS32, MIPS only] If this variable is defined, then certain
3711		low level initializations (like setting up the memory
3712		controller) are omitted and/or U-Boot does not
3713		relocate itself into RAM.
3714
3715		Normally this variable MUST NOT be defined. The only
3716		exception is when U-Boot is loaded (to RAM) by some
3717		other boot loader or by a debugger which performs
3718		these initializations itself.
3719
3720- CONFIG_SKIP_LOWLEVEL_INIT_ONLY
3721		[ARM926EJ-S only] This allows just the call to lowlevel_init()
3722		to be skipped. The normal CP15 init (such as enabling the
3723		instruction cache) is still performed.
3724
3725- CONFIG_SPL_BUILD
3726		Modifies the behaviour of start.S when compiling a loader
3727		that is executed before the actual U-Boot. E.g. when
3728		compiling a NAND SPL.
3729
3730- CONFIG_TPL_BUILD
3731		Modifies the behaviour of start.S  when compiling a loader
3732		that is executed after the SPL and before the actual U-Boot.
3733		It is loaded by the SPL.
3734
3735- CONFIG_SYS_MPC85XX_NO_RESETVEC
3736		Only for 85xx systems. If this variable is specified, the section
3737		.resetvec is not kept and the section .bootpg is placed in the
3738		previous 4k of the .text section.
3739
3740- CONFIG_ARCH_MAP_SYSMEM
3741		Generally U-Boot (and in particular the md command) uses
3742		effective address. It is therefore not necessary to regard
3743		U-Boot address as virtual addresses that need to be translated
3744		to physical addresses. However, sandbox requires this, since
3745		it maintains its own little RAM buffer which contains all
3746		addressable memory. This option causes some memory accesses
3747		to be mapped through map_sysmem() / unmap_sysmem().
3748
3749- CONFIG_X86_RESET_VECTOR
3750		If defined, the x86 reset vector code is included. This is not
3751		needed when U-Boot is running from Coreboot.
3752
3753- CONFIG_SPL_AM33XX_ENABLE_RTC32K_OSC:
3754		Enables the RTC32K OSC on AM33xx based plattforms
3755
3756- CONFIG_SYS_NAND_NO_SUBPAGE_WRITE
3757		Option to disable subpage write in NAND driver
3758		driver that uses this:
3759		drivers/mtd/nand/davinci_nand.c
3760
3761Freescale QE/FMAN Firmware Support:
3762-----------------------------------
3763
3764The Freescale QUICCEngine (QE) and Frame Manager (FMAN) both support the
3765loading of "firmware", which is encoded in the QE firmware binary format.
3766This firmware often needs to be loaded during U-Boot booting, so macros
3767are used to identify the storage device (NOR flash, SPI, etc) and the address
3768within that device.
3769
3770- CONFIG_SYS_FMAN_FW_ADDR
3771	The address in the storage device where the FMAN microcode is located.  The
3772	meaning of this address depends on which CONFIG_SYS_QE_FW_IN_xxx macro
3773	is also specified.
3774
3775- CONFIG_SYS_QE_FW_ADDR
3776	The address in the storage device where the QE microcode is located.  The
3777	meaning of this address depends on which CONFIG_SYS_QE_FW_IN_xxx macro
3778	is also specified.
3779
3780- CONFIG_SYS_QE_FMAN_FW_LENGTH
3781	The maximum possible size of the firmware.  The firmware binary format
3782	has a field that specifies the actual size of the firmware, but it
3783	might not be possible to read any part of the firmware unless some
3784	local storage is allocated to hold the entire firmware first.
3785
3786- CONFIG_SYS_QE_FMAN_FW_IN_NOR
3787	Specifies that QE/FMAN firmware is located in NOR flash, mapped as
3788	normal addressable memory via the LBC.  CONFIG_SYS_FMAN_FW_ADDR is the
3789	virtual address in NOR flash.
3790
3791- CONFIG_SYS_QE_FMAN_FW_IN_NAND
3792	Specifies that QE/FMAN firmware is located in NAND flash.
3793	CONFIG_SYS_FMAN_FW_ADDR is the offset within NAND flash.
3794
3795- CONFIG_SYS_QE_FMAN_FW_IN_MMC
3796	Specifies that QE/FMAN firmware is located on the primary SD/MMC
3797	device.  CONFIG_SYS_FMAN_FW_ADDR is the byte offset on that device.
3798
3799- CONFIG_SYS_QE_FMAN_FW_IN_REMOTE
3800	Specifies that QE/FMAN firmware is located in the remote (master)
3801	memory space.	CONFIG_SYS_FMAN_FW_ADDR is a virtual address which
3802	can be mapped from slave TLB->slave LAW->slave SRIO or PCIE outbound
3803	window->master inbound window->master LAW->the ucode address in
3804	master's memory space.
3805
3806Freescale Layerscape Management Complex Firmware Support:
3807---------------------------------------------------------
3808The Freescale Layerscape Management Complex (MC) supports the loading of
3809"firmware".
3810This firmware often needs to be loaded during U-Boot booting, so macros
3811are used to identify the storage device (NOR flash, SPI, etc) and the address
3812within that device.
3813
3814- CONFIG_FSL_MC_ENET
3815	Enable the MC driver for Layerscape SoCs.
3816
3817Freescale Layerscape Debug Server Support:
3818-------------------------------------------
3819The Freescale Layerscape Debug Server Support supports the loading of
3820"Debug Server firmware" and triggering SP boot-rom.
3821This firmware often needs to be loaded during U-Boot booting.
3822
3823- CONFIG_SYS_MC_RSV_MEM_ALIGN
3824	Define alignment of reserved memory MC requires
3825
3826Reproducible builds
3827-------------------
3828
3829In order to achieve reproducible builds, timestamps used in the U-Boot build
3830process have to be set to a fixed value.
3831
3832This is done using the SOURCE_DATE_EPOCH environment variable.
3833SOURCE_DATE_EPOCH is to be set on the build host's shell, not as a configuration
3834option for U-Boot or an environment variable in U-Boot.
3835
3836SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC.
3837
3838Building the Software:
3839======================
3840
3841Building U-Boot has been tested in several native build environments
3842and in many different cross environments. Of course we cannot support
3843all possibly existing versions of cross development tools in all
3844(potentially obsolete) versions. In case of tool chain problems we
3845recommend to use the ELDK (see http://www.denx.de/wiki/DULG/ELDK)
3846which is extensively used to build and test U-Boot.
3847
3848If you are not using a native environment, it is assumed that you
3849have GNU cross compiling tools available in your path. In this case,
3850you must set the environment variable CROSS_COMPILE in your shell.
3851Note that no changes to the Makefile or any other source files are
3852necessary. For example using the ELDK on a 4xx CPU, please enter:
3853
3854	$ CROSS_COMPILE=ppc_4xx-
3855	$ export CROSS_COMPILE
3856
3857Note: If you wish to generate Windows versions of the utilities in
3858      the tools directory you can use the MinGW toolchain
3859      (http://www.mingw.org).  Set your HOST tools to the MinGW
3860      toolchain and execute 'make tools'.  For example:
3861
3862       $ make HOSTCC=i586-mingw32msvc-gcc HOSTSTRIP=i586-mingw32msvc-strip tools
3863
3864      Binaries such as tools/mkimage.exe will be created which can
3865      be executed on computers running Windows.
3866
3867U-Boot is intended to be simple to build. After installing the
3868sources you must configure U-Boot for one specific board type. This
3869is done by typing:
3870
3871	make NAME_defconfig
3872
3873where "NAME_defconfig" is the name of one of the existing configu-
3874rations; see boards.cfg for supported names.
3875
3876Note: for some board special configuration names may exist; check if
3877      additional information is available from the board vendor; for
3878      instance, the TQM823L systems are available without (standard)
3879      or with LCD support. You can select such additional "features"
3880      when choosing the configuration, i. e.
3881
3882      make TQM823L_defconfig
3883	- will configure for a plain TQM823L, i. e. no LCD support
3884
3885      make TQM823L_LCD_defconfig
3886	- will configure for a TQM823L with U-Boot console on LCD
3887
3888      etc.
3889
3890
3891Finally, type "make all", and you should get some working U-Boot
3892images ready for download to / installation on your system:
3893
3894- "u-boot.bin" is a raw binary image
3895- "u-boot" is an image in ELF binary format
3896- "u-boot.srec" is in Motorola S-Record format
3897
3898By default the build is performed locally and the objects are saved
3899in the source directory. One of the two methods can be used to change
3900this behavior and build U-Boot to some external directory:
3901
39021. Add O= to the make command line invocations:
3903
3904	make O=/tmp/build distclean
3905	make O=/tmp/build NAME_defconfig
3906	make O=/tmp/build all
3907
39082. Set environment variable KBUILD_OUTPUT to point to the desired location:
3909
3910	export KBUILD_OUTPUT=/tmp/build
3911	make distclean
3912	make NAME_defconfig
3913	make all
3914
3915Note that the command line "O=" setting overrides the KBUILD_OUTPUT environment
3916variable.
3917
3918
3919Please be aware that the Makefiles assume you are using GNU make, so
3920for instance on NetBSD you might need to use "gmake" instead of
3921native "make".
3922
3923
3924If the system board that you have is not listed, then you will need
3925to port U-Boot to your hardware platform. To do this, follow these
3926steps:
3927
39281.  Create a new directory to hold your board specific code. Add any
3929    files you need. In your board directory, you will need at least
3930    the "Makefile" and a "<board>.c".
39312.  Create a new configuration file "include/configs/<board>.h" for
3932    your board.
39333.  If you're porting U-Boot to a new CPU, then also create a new
3934    directory to hold your CPU specific code. Add any files you need.
39354.  Run "make <board>_defconfig" with your new name.
39365.  Type "make", and you should get a working "u-boot.srec" file
3937    to be installed on your target system.
39386.  Debug and solve any problems that might arise.
3939    [Of course, this last step is much harder than it sounds.]
3940
3941
3942Testing of U-Boot Modifications, Ports to New Hardware, etc.:
3943==============================================================
3944
3945If you have modified U-Boot sources (for instance added a new board
3946or support for new devices, a new CPU, etc.) you are expected to
3947provide feedback to the other developers. The feedback normally takes
3948the form of a "patch", i. e. a context diff against a certain (latest
3949official or latest in the git repository) version of U-Boot sources.
3950
3951But before you submit such a patch, please verify that your modifi-
3952cation did not break existing code. At least make sure that *ALL* of
3953the supported boards compile WITHOUT ANY compiler warnings. To do so,
3954just run the buildman script (tools/buildman/buildman), which will
3955configure and build U-Boot for ALL supported system. Be warned, this
3956will take a while. Please see the buildman README, or run 'buildman -H'
3957for documentation.
3958
3959
3960See also "U-Boot Porting Guide" below.
3961
3962
3963Monitor Commands - Overview:
3964============================
3965
3966go	- start application at address 'addr'
3967run	- run commands in an environment variable
3968bootm	- boot application image from memory
3969bootp	- boot image via network using BootP/TFTP protocol
3970bootz   - boot zImage from memory
3971tftpboot- boot image via network using TFTP protocol
3972	       and env variables "ipaddr" and "serverip"
3973	       (and eventually "gatewayip")
3974tftpput - upload a file via network using TFTP protocol
3975rarpboot- boot image via network using RARP/TFTP protocol
3976diskboot- boot from IDE devicebootd   - boot default, i.e., run 'bootcmd'
3977loads	- load S-Record file over serial line
3978loadb	- load binary file over serial line (kermit mode)
3979md	- memory display
3980mm	- memory modify (auto-incrementing)
3981nm	- memory modify (constant address)
3982mw	- memory write (fill)
3983cp	- memory copy
3984cmp	- memory compare
3985crc32	- checksum calculation
3986i2c	- I2C sub-system
3987sspi	- SPI utility commands
3988base	- print or set address offset
3989printenv- print environment variables
3990setenv	- set environment variables
3991saveenv - save environment variables to persistent storage
3992protect - enable or disable FLASH write protection
3993erase	- erase FLASH memory
3994flinfo	- print FLASH memory information
3995nand	- NAND memory operations (see doc/README.nand)
3996bdinfo	- print Board Info structure
3997iminfo	- print header information for application image
3998coninfo - print console devices and informations
3999ide	- IDE sub-system
4000loop	- infinite loop on address range
4001loopw	- infinite write loop on address range
4002mtest	- simple RAM test
4003icache	- enable or disable instruction cache
4004dcache	- enable or disable data cache
4005reset	- Perform RESET of the CPU
4006echo	- echo args to console
4007version - print monitor version
4008help	- print online help
4009?	- alias for 'help'
4010
4011
4012Monitor Commands - Detailed Description:
4013========================================
4014
4015TODO.
4016
4017For now: just type "help <command>".
4018
4019
4020Environment Variables:
4021======================
4022
4023U-Boot supports user configuration using Environment Variables which
4024can be made persistent by saving to Flash memory.
4025
4026Environment Variables are set using "setenv", printed using
4027"printenv", and saved to Flash using "saveenv". Using "setenv"
4028without a value can be used to delete a variable from the
4029environment. As long as you don't save the environment you are
4030working with an in-memory copy. In case the Flash area containing the
4031environment is erased by accident, a default environment is provided.
4032
4033Some configuration options can be set using Environment Variables.
4034
4035List of environment variables (most likely not complete):
4036
4037  baudrate	- see CONFIG_BAUDRATE
4038
4039  bootdelay	- see CONFIG_BOOTDELAY
4040
4041  bootcmd	- see CONFIG_BOOTCOMMAND
4042
4043  bootargs	- Boot arguments when booting an RTOS image
4044
4045  bootfile	- Name of the image to load with TFTP
4046
4047  bootm_low	- Memory range available for image processing in the bootm
4048		  command can be restricted. This variable is given as
4049		  a hexadecimal number and defines lowest address allowed
4050		  for use by the bootm command. See also "bootm_size"
4051		  environment variable. Address defined by "bootm_low" is
4052		  also the base of the initial memory mapping for the Linux
4053		  kernel -- see the description of CONFIG_SYS_BOOTMAPSZ and
4054		  bootm_mapsize.
4055
4056  bootm_mapsize - Size of the initial memory mapping for the Linux kernel.
4057		  This variable is given as a hexadecimal number and it
4058		  defines the size of the memory region starting at base
4059		  address bootm_low that is accessible by the Linux kernel
4060		  during early boot.  If unset, CONFIG_SYS_BOOTMAPSZ is used
4061		  as the default value if it is defined, and bootm_size is
4062		  used otherwise.
4063
4064  bootm_size	- Memory range available for image processing in the bootm
4065		  command can be restricted. This variable is given as
4066		  a hexadecimal number and defines the size of the region
4067		  allowed for use by the bootm command. See also "bootm_low"
4068		  environment variable.
4069
4070  updatefile	- Location of the software update file on a TFTP server, used
4071		  by the automatic software update feature. Please refer to
4072		  documentation in doc/README.update for more details.
4073
4074  autoload	- if set to "no" (any string beginning with 'n'),
4075		  "bootp" will just load perform a lookup of the
4076		  configuration from the BOOTP server, but not try to
4077		  load any image using TFTP
4078
4079  autostart	- if set to "yes", an image loaded using the "bootp",
4080		  "rarpboot", "tftpboot" or "diskboot" commands will
4081		  be automatically started (by internally calling
4082		  "bootm")
4083
4084		  If set to "no", a standalone image passed to the
4085		  "bootm" command will be copied to the load address
4086		  (and eventually uncompressed), but NOT be started.
4087		  This can be used to load and uncompress arbitrary
4088		  data.
4089
4090  fdt_high	- if set this restricts the maximum address that the
4091		  flattened device tree will be copied into upon boot.
4092		  For example, if you have a system with 1 GB memory
4093		  at physical address 0x10000000, while Linux kernel
4094		  only recognizes the first 704 MB as low memory, you
4095		  may need to set fdt_high as 0x3C000000 to have the
4096		  device tree blob be copied to the maximum address
4097		  of the 704 MB low memory, so that Linux kernel can
4098		  access it during the boot procedure.
4099
4100		  If this is set to the special value 0xFFFFFFFF then
4101		  the fdt will not be copied at all on boot.  For this
4102		  to work it must reside in writable memory, have
4103		  sufficient padding on the end of it for u-boot to
4104		  add the information it needs into it, and the memory
4105		  must be accessible by the kernel.
4106
4107  fdtcontroladdr- if set this is the address of the control flattened
4108		  device tree used by U-Boot when CONFIG_OF_CONTROL is
4109		  defined.
4110
4111  i2cfast	- (PPC405GP|PPC405EP only)
4112		  if set to 'y' configures Linux I2C driver for fast
4113		  mode (400kHZ). This environment variable is used in
4114		  initialization code. So, for changes to be effective
4115		  it must be saved and board must be reset.
4116
4117  initrd_high	- restrict positioning of initrd images:
4118		  If this variable is not set, initrd images will be
4119		  copied to the highest possible address in RAM; this
4120		  is usually what you want since it allows for
4121		  maximum initrd size. If for some reason you want to
4122		  make sure that the initrd image is loaded below the
4123		  CONFIG_SYS_BOOTMAPSZ limit, you can set this environment
4124		  variable to a value of "no" or "off" or "0".
4125		  Alternatively, you can set it to a maximum upper
4126		  address to use (U-Boot will still check that it
4127		  does not overwrite the U-Boot stack and data).
4128
4129		  For instance, when you have a system with 16 MB
4130		  RAM, and want to reserve 4 MB from use by Linux,
4131		  you can do this by adding "mem=12M" to the value of
4132		  the "bootargs" variable. However, now you must make
4133		  sure that the initrd image is placed in the first
4134		  12 MB as well - this can be done with
4135
4136		  setenv initrd_high 00c00000
4137
4138		  If you set initrd_high to 0xFFFFFFFF, this is an
4139		  indication to U-Boot that all addresses are legal
4140		  for the Linux kernel, including addresses in flash
4141		  memory. In this case U-Boot will NOT COPY the
4142		  ramdisk at all. This may be useful to reduce the
4143		  boot time on your system, but requires that this
4144		  feature is supported by your Linux kernel.
4145
4146  ipaddr	- IP address; needed for tftpboot command
4147
4148  loadaddr	- Default load address for commands like "bootp",
4149		  "rarpboot", "tftpboot", "loadb" or "diskboot"
4150
4151  loads_echo	- see CONFIG_LOADS_ECHO
4152
4153  serverip	- TFTP server IP address; needed for tftpboot command
4154
4155  bootretry	- see CONFIG_BOOT_RETRY_TIME
4156
4157  bootdelaykey	- see CONFIG_AUTOBOOT_DELAY_STR
4158
4159  bootstopkey	- see CONFIG_AUTOBOOT_STOP_STR
4160
4161  ethprime	- controls which interface is used first.
4162
4163  ethact	- controls which interface is currently active.
4164		  For example you can do the following
4165
4166		  => setenv ethact FEC
4167		  => ping 192.168.0.1 # traffic sent on FEC
4168		  => setenv ethact SCC
4169		  => ping 10.0.0.1 # traffic sent on SCC
4170
4171  ethrotate	- When set to "no" U-Boot does not go through all
4172		  available network interfaces.
4173		  It just stays at the currently selected interface.
4174
4175  netretry	- When set to "no" each network operation will
4176		  either succeed or fail without retrying.
4177		  When set to "once" the network operation will
4178		  fail when all the available network interfaces
4179		  are tried once without success.
4180		  Useful on scripts which control the retry operation
4181		  themselves.
4182
4183  npe_ucode	- set load address for the NPE microcode
4184
4185  silent_linux  - If set then Linux will be told to boot silently, by
4186		  changing the console to be empty. If "yes" it will be
4187		  made silent. If "no" it will not be made silent. If
4188		  unset, then it will be made silent if the U-Boot console
4189		  is silent.
4190
4191  tftpsrcp	- If this is set, the value is used for TFTP's
4192		  UDP source port.
4193
4194  tftpdstp	- If this is set, the value is used for TFTP's UDP
4195		  destination port instead of the Well Know Port 69.
4196
4197  tftpblocksize - Block size to use for TFTP transfers; if not set,
4198		  we use the TFTP server's default block size
4199
4200  tftptimeout	- Retransmission timeout for TFTP packets (in milli-
4201		  seconds, minimum value is 1000 = 1 second). Defines
4202		  when a packet is considered to be lost so it has to
4203		  be retransmitted. The default is 5000 = 5 seconds.
4204		  Lowering this value may make downloads succeed
4205		  faster in networks with high packet loss rates or
4206		  with unreliable TFTP servers.
4207
4208  tftptimeoutcountmax	- maximum count of TFTP timeouts (no
4209		  unit, minimum value = 0). Defines how many timeouts
4210		  can happen during a single file transfer before that
4211		  transfer is aborted. The default is 10, and 0 means
4212		  'no timeouts allowed'. Increasing this value may help
4213		  downloads succeed with high packet loss rates, or with
4214		  unreliable TFTP servers or client hardware.
4215
4216  vlan		- When set to a value < 4095 the traffic over
4217		  Ethernet is encapsulated/received over 802.1q
4218		  VLAN tagged frames.
4219
4220  bootpretryperiod	- Period during which BOOTP/DHCP sends retries.
4221		  Unsigned value, in milliseconds. If not set, the period will
4222		  be either the default (28000), or a value based on
4223		  CONFIG_NET_RETRY_COUNT, if defined. This value has
4224		  precedence over the valu based on CONFIG_NET_RETRY_COUNT.
4225
4226The following image location variables contain the location of images
4227used in booting. The "Image" column gives the role of the image and is
4228not an environment variable name. The other columns are environment
4229variable names. "File Name" gives the name of the file on a TFTP
4230server, "RAM Address" gives the location in RAM the image will be
4231loaded to, and "Flash Location" gives the image's address in NOR
4232flash or offset in NAND flash.
4233
4234*Note* - these variables don't have to be defined for all boards, some
4235boards currently use other variables for these purposes, and some
4236boards use these variables for other purposes.
4237
4238Image		    File Name	     RAM Address       Flash Location
4239-----		    ---------	     -----------       --------------
4240u-boot		    u-boot	     u-boot_addr_r     u-boot_addr
4241Linux kernel	    bootfile	     kernel_addr_r     kernel_addr
4242device tree blob    fdtfile	     fdt_addr_r	       fdt_addr
4243ramdisk		    ramdiskfile	     ramdisk_addr_r    ramdisk_addr
4244
4245The following environment variables may be used and automatically
4246updated by the network boot commands ("bootp" and "rarpboot"),
4247depending the information provided by your boot server:
4248
4249  bootfile	- see above
4250  dnsip		- IP address of your Domain Name Server
4251  dnsip2	- IP address of your secondary Domain Name Server
4252  gatewayip	- IP address of the Gateway (Router) to use
4253  hostname	- Target hostname
4254  ipaddr	- see above
4255  netmask	- Subnet Mask
4256  rootpath	- Pathname of the root filesystem on the NFS server
4257  serverip	- see above
4258
4259
4260There are two special Environment Variables:
4261
4262  serial#	- contains hardware identification information such
4263		  as type string and/or serial number
4264  ethaddr	- Ethernet address
4265
4266These variables can be set only once (usually during manufacturing of
4267the board). U-Boot refuses to delete or overwrite these variables
4268once they have been set once.
4269
4270
4271Further special Environment Variables:
4272
4273  ver		- Contains the U-Boot version string as printed
4274		  with the "version" command. This variable is
4275		  readonly (see CONFIG_VERSION_VARIABLE).
4276
4277
4278Please note that changes to some configuration parameters may take
4279only effect after the next boot (yes, that's just like Windoze :-).
4280
4281
4282Callback functions for environment variables:
4283---------------------------------------------
4284
4285For some environment variables, the behavior of u-boot needs to change
4286when their values are changed.  This functionality allows functions to
4287be associated with arbitrary variables.  On creation, overwrite, or
4288deletion, the callback will provide the opportunity for some side
4289effect to happen or for the change to be rejected.
4290
4291The callbacks are named and associated with a function using the
4292U_BOOT_ENV_CALLBACK macro in your board or driver code.
4293
4294These callbacks are associated with variables in one of two ways.  The
4295static list can be added to by defining CONFIG_ENV_CALLBACK_LIST_STATIC
4296in the board configuration to a string that defines a list of
4297associations.  The list must be in the following format:
4298
4299	entry = variable_name[:callback_name]
4300	list = entry[,list]
4301
4302If the callback name is not specified, then the callback is deleted.
4303Spaces are also allowed anywhere in the list.
4304
4305Callbacks can also be associated by defining the ".callbacks" variable
4306with the same list format above.  Any association in ".callbacks" will
4307override any association in the static list. You can define
4308CONFIG_ENV_CALLBACK_LIST_DEFAULT to a list (string) to define the
4309".callbacks" environment variable in the default or embedded environment.
4310
4311If CONFIG_REGEX is defined, the variable_name above is evaluated as a
4312regular expression. This allows multiple variables to be connected to
4313the same callback without explicitly listing them all out.
4314
4315
4316Command Line Parsing:
4317=====================
4318
4319There are two different command line parsers available with U-Boot:
4320the old "simple" one, and the much more powerful "hush" shell:
4321
4322Old, simple command line parser:
4323--------------------------------
4324
4325- supports environment variables (through setenv / saveenv commands)
4326- several commands on one line, separated by ';'
4327- variable substitution using "... ${name} ..." syntax
4328- special characters ('$', ';') can be escaped by prefixing with '\',
4329  for example:
4330	setenv bootcmd bootm \${address}
4331- You can also escape text by enclosing in single apostrophes, for example:
4332	setenv addip 'setenv bootargs $bootargs ip=$ipaddr:$serverip:$gatewayip:$netmask:$hostname::off'
4333
4334Hush shell:
4335-----------
4336
4337- similar to Bourne shell, with control structures like
4338  if...then...else...fi, for...do...done; while...do...done,
4339  until...do...done, ...
4340- supports environment ("global") variables (through setenv / saveenv
4341  commands) and local shell variables (through standard shell syntax
4342  "name=value"); only environment variables can be used with "run"
4343  command
4344
4345General rules:
4346--------------
4347
4348(1) If a command line (or an environment variable executed by a "run"
4349    command) contains several commands separated by semicolon, and
4350    one of these commands fails, then the remaining commands will be
4351    executed anyway.
4352
4353(2) If you execute several variables with one call to run (i. e.
4354    calling run with a list of variables as arguments), any failing
4355    command will cause "run" to terminate, i. e. the remaining
4356    variables are not executed.
4357
4358Note for Redundant Ethernet Interfaces:
4359=======================================
4360
4361Some boards come with redundant Ethernet interfaces; U-Boot supports
4362such configurations and is capable of automatic selection of a
4363"working" interface when needed. MAC assignment works as follows:
4364
4365Network interfaces are numbered eth0, eth1, eth2, ... Corresponding
4366MAC addresses can be stored in the environment as "ethaddr" (=>eth0),
4367"eth1addr" (=>eth1), "eth2addr", ...
4368
4369If the network interface stores some valid MAC address (for instance
4370in SROM), this is used as default address if there is NO correspon-
4371ding setting in the environment; if the corresponding environment
4372variable is set, this overrides the settings in the card; that means:
4373
4374o If the SROM has a valid MAC address, and there is no address in the
4375  environment, the SROM's address is used.
4376
4377o If there is no valid address in the SROM, and a definition in the
4378  environment exists, then the value from the environment variable is
4379  used.
4380
4381o If both the SROM and the environment contain a MAC address, and
4382  both addresses are the same, this MAC address is used.
4383
4384o If both the SROM and the environment contain a MAC address, and the
4385  addresses differ, the value from the environment is used and a
4386  warning is printed.
4387
4388o If neither SROM nor the environment contain a MAC address, an error
4389  is raised. If CONFIG_NET_RANDOM_ETHADDR is defined, then in this case
4390  a random, locally-assigned MAC is used.
4391
4392If Ethernet drivers implement the 'write_hwaddr' function, valid MAC addresses
4393will be programmed into hardware as part of the initialization process.	 This
4394may be skipped by setting the appropriate 'ethmacskip' environment variable.
4395The naming convention is as follows:
4396"ethmacskip" (=>eth0), "eth1macskip" (=>eth1) etc.
4397
4398Image Formats:
4399==============
4400
4401U-Boot is capable of booting (and performing other auxiliary operations on)
4402images in two formats:
4403
4404New uImage format (FIT)
4405-----------------------
4406
4407Flexible and powerful format based on Flattened Image Tree -- FIT (similar
4408to Flattened Device Tree). It allows the use of images with multiple
4409components (several kernels, ramdisks, etc.), with contents protected by
4410SHA1, MD5 or CRC32. More details are found in the doc/uImage.FIT directory.
4411
4412
4413Old uImage format
4414-----------------
4415
4416Old image format is based on binary files which can be basically anything,
4417preceded by a special header; see the definitions in include/image.h for
4418details; basically, the header defines the following image properties:
4419
4420* Target Operating System (Provisions for OpenBSD, NetBSD, FreeBSD,
4421  4.4BSD, Linux, SVR4, Esix, Solaris, Irix, SCO, Dell, NCR, VxWorks,
4422  LynxOS, pSOS, QNX, RTEMS, INTEGRITY;
4423  Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, LynxOS,
4424  INTEGRITY).
4425* Target CPU Architecture (Provisions for Alpha, ARM, Intel x86,
4426  IA64, MIPS, NDS32, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
4427  Currently supported: ARM, Intel x86, MIPS, NDS32, Nios II, PowerPC).
4428* Compression Type (uncompressed, gzip, bzip2)
4429* Load Address
4430* Entry Point
4431* Image Name
4432* Image Timestamp
4433
4434The header is marked by a special Magic Number, and both the header
4435and the data portions of the image are secured against corruption by
4436CRC32 checksums.
4437
4438
4439Linux Support:
4440==============
4441
4442Although U-Boot should support any OS or standalone application
4443easily, the main focus has always been on Linux during the design of
4444U-Boot.
4445
4446U-Boot includes many features that so far have been part of some
4447special "boot loader" code within the Linux kernel. Also, any
4448"initrd" images to be used are no longer part of one big Linux image;
4449instead, kernel and "initrd" are separate images. This implementation
4450serves several purposes:
4451
4452- the same features can be used for other OS or standalone
4453  applications (for instance: using compressed images to reduce the
4454  Flash memory footprint)
4455
4456- it becomes much easier to port new Linux kernel versions because
4457  lots of low-level, hardware dependent stuff are done by U-Boot
4458
4459- the same Linux kernel image can now be used with different "initrd"
4460  images; of course this also means that different kernel images can
4461  be run with the same "initrd". This makes testing easier (you don't
4462  have to build a new "zImage.initrd" Linux image when you just
4463  change a file in your "initrd"). Also, a field-upgrade of the
4464  software is easier now.
4465
4466
4467Linux HOWTO:
4468============
4469
4470Porting Linux to U-Boot based systems:
4471---------------------------------------
4472
4473U-Boot cannot save you from doing all the necessary modifications to
4474configure the Linux device drivers for use with your target hardware
4475(no, we don't intend to provide a full virtual machine interface to
4476Linux :-).
4477
4478But now you can ignore ALL boot loader code (in arch/powerpc/mbxboot).
4479
4480Just make sure your machine specific header file (for instance
4481include/asm-ppc/tqm8xx.h) includes the same definition of the Board
4482Information structure as we define in include/asm-<arch>/u-boot.h,
4483and make sure that your definition of IMAP_ADDR uses the same value
4484as your U-Boot configuration in CONFIG_SYS_IMMR.
4485
4486Note that U-Boot now has a driver model, a unified model for drivers.
4487If you are adding a new driver, plumb it into driver model. If there
4488is no uclass available, you are encouraged to create one. See
4489doc/driver-model.
4490
4491
4492Configuring the Linux kernel:
4493-----------------------------
4494
4495No specific requirements for U-Boot. Make sure you have some root
4496device (initial ramdisk, NFS) for your target system.
4497
4498
4499Building a Linux Image:
4500-----------------------
4501
4502With U-Boot, "normal" build targets like "zImage" or "bzImage" are
4503not used. If you use recent kernel source, a new build target
4504"uImage" will exist which automatically builds an image usable by
4505U-Boot. Most older kernels also have support for a "pImage" target,
4506which was introduced for our predecessor project PPCBoot and uses a
4507100% compatible format.
4508
4509Example:
4510
4511	make TQM850L_defconfig
4512	make oldconfig
4513	make dep
4514	make uImage
4515
4516The "uImage" build target uses a special tool (in 'tools/mkimage') to
4517encapsulate a compressed Linux kernel image with header	 information,
4518CRC32 checksum etc. for use with U-Boot. This is what we are doing:
4519
4520* build a standard "vmlinux" kernel image (in ELF binary format):
4521
4522* convert the kernel into a raw binary image:
4523
4524	${CROSS_COMPILE}-objcopy -O binary \
4525				 -R .note -R .comment \
4526				 -S vmlinux linux.bin
4527
4528* compress the binary image:
4529
4530	gzip -9 linux.bin
4531
4532* package compressed binary image for U-Boot:
4533
4534	mkimage -A ppc -O linux -T kernel -C gzip \
4535		-a 0 -e 0 -n "Linux Kernel Image" \
4536		-d linux.bin.gz uImage
4537
4538
4539The "mkimage" tool can also be used to create ramdisk images for use
4540with U-Boot, either separated from the Linux kernel image, or
4541combined into one file. "mkimage" encapsulates the images with a 64
4542byte header containing information about target architecture,
4543operating system, image type, compression method, entry points, time
4544stamp, CRC32 checksums, etc.
4545
4546"mkimage" can be called in two ways: to verify existing images and
4547print the header information, or to build new images.
4548
4549In the first form (with "-l" option) mkimage lists the information
4550contained in the header of an existing U-Boot image; this includes
4551checksum verification:
4552
4553	tools/mkimage -l image
4554	  -l ==> list image header information
4555
4556The second form (with "-d" option) is used to build a U-Boot image
4557from a "data file" which is used as image payload:
4558
4559	tools/mkimage -A arch -O os -T type -C comp -a addr -e ep \
4560		      -n name -d data_file image
4561	  -A ==> set architecture to 'arch'
4562	  -O ==> set operating system to 'os'
4563	  -T ==> set image type to 'type'
4564	  -C ==> set compression type 'comp'
4565	  -a ==> set load address to 'addr' (hex)
4566	  -e ==> set entry point to 'ep' (hex)
4567	  -n ==> set image name to 'name'
4568	  -d ==> use image data from 'datafile'
4569
4570Right now, all Linux kernels for PowerPC systems use the same load
4571address (0x00000000), but the entry point address depends on the
4572kernel version:
4573
4574- 2.2.x kernels have the entry point at 0x0000000C,
4575- 2.3.x and later kernels have the entry point at 0x00000000.
4576
4577So a typical call to build a U-Boot image would read:
4578
4579	-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
4580	> -A ppc -O linux -T kernel -C gzip -a 0 -e 0 \
4581	> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz \
4582	> examples/uImage.TQM850L
4583	Image Name:   2.4.4 kernel for TQM850L
4584	Created:      Wed Jul 19 02:34:59 2000
4585	Image Type:   PowerPC Linux Kernel Image (gzip compressed)
4586	Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
4587	Load Address: 0x00000000
4588	Entry Point:  0x00000000
4589
4590To verify the contents of the image (or check for corruption):
4591
4592	-> tools/mkimage -l examples/uImage.TQM850L
4593	Image Name:   2.4.4 kernel for TQM850L
4594	Created:      Wed Jul 19 02:34:59 2000
4595	Image Type:   PowerPC Linux Kernel Image (gzip compressed)
4596	Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
4597	Load Address: 0x00000000
4598	Entry Point:  0x00000000
4599
4600NOTE: for embedded systems where boot time is critical you can trade
4601speed for memory and install an UNCOMPRESSED image instead: this
4602needs more space in Flash, but boots much faster since it does not
4603need to be uncompressed:
4604
4605	-> gunzip /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz
4606	-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
4607	> -A ppc -O linux -T kernel -C none -a 0 -e 0 \
4608	> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux \
4609	> examples/uImage.TQM850L-uncompressed
4610	Image Name:   2.4.4 kernel for TQM850L
4611	Created:      Wed Jul 19 02:34:59 2000
4612	Image Type:   PowerPC Linux Kernel Image (uncompressed)
4613	Data Size:    792160 Bytes = 773.59 kB = 0.76 MB
4614	Load Address: 0x00000000
4615	Entry Point:  0x00000000
4616
4617
4618Similar you can build U-Boot images from a 'ramdisk.image.gz' file
4619when your kernel is intended to use an initial ramdisk:
4620
4621	-> tools/mkimage -n 'Simple Ramdisk Image' \
4622	> -A ppc -O linux -T ramdisk -C gzip \
4623	> -d /LinuxPPC/images/SIMPLE-ramdisk.image.gz examples/simple-initrd
4624	Image Name:   Simple Ramdisk Image
4625	Created:      Wed Jan 12 14:01:50 2000
4626	Image Type:   PowerPC Linux RAMDisk Image (gzip compressed)
4627	Data Size:    566530 Bytes = 553.25 kB = 0.54 MB
4628	Load Address: 0x00000000
4629	Entry Point:  0x00000000
4630
4631The "dumpimage" is a tool to disassemble images built by mkimage. Its "-i"
4632option performs the converse operation of the mkimage's second form (the "-d"
4633option). Given an image built by mkimage, the dumpimage extracts a "data file"
4634from the image:
4635
4636	tools/dumpimage -i image -T type -p position data_file
4637	  -i ==> extract from the 'image' a specific 'data_file'
4638	  -T ==> set image type to 'type'
4639	  -p ==> 'position' (starting at 0) of the 'data_file' inside the 'image'
4640
4641
4642Installing a Linux Image:
4643-------------------------
4644
4645To downloading a U-Boot image over the serial (console) interface,
4646you must convert the image to S-Record format:
4647
4648	objcopy -I binary -O srec examples/image examples/image.srec
4649
4650The 'objcopy' does not understand the information in the U-Boot
4651image header, so the resulting S-Record file will be relative to
4652address 0x00000000. To load it to a given address, you need to
4653specify the target address as 'offset' parameter with the 'loads'
4654command.
4655
4656Example: install the image to address 0x40100000 (which on the
4657TQM8xxL is in the first Flash bank):
4658
4659	=> erase 40100000 401FFFFF
4660
4661	.......... done
4662	Erased 8 sectors
4663
4664	=> loads 40100000
4665	## Ready for S-Record download ...
4666	~>examples/image.srec
4667	1 2 3 4 5 6 7 8 9 10 11 12 13 ...
4668	...
4669	15989 15990 15991 15992
4670	[file transfer complete]
4671	[connected]
4672	## Start Addr = 0x00000000
4673
4674
4675You can check the success of the download using the 'iminfo' command;
4676this includes a checksum verification so you can be sure no data
4677corruption happened:
4678
4679	=> imi 40100000
4680
4681	## Checking Image at 40100000 ...
4682	   Image Name:	 2.2.13 for initrd on TQM850L
4683	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4684	   Data Size:	 335725 Bytes = 327 kB = 0 MB
4685	   Load Address: 00000000
4686	   Entry Point:	 0000000c
4687	   Verifying Checksum ... OK
4688
4689
4690Boot Linux:
4691-----------
4692
4693The "bootm" command is used to boot an application that is stored in
4694memory (RAM or Flash). In case of a Linux kernel image, the contents
4695of the "bootargs" environment variable is passed to the kernel as
4696parameters. You can check and modify this variable using the
4697"printenv" and "setenv" commands:
4698
4699
4700	=> printenv bootargs
4701	bootargs=root=/dev/ram
4702
4703	=> setenv bootargs root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
4704
4705	=> printenv bootargs
4706	bootargs=root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
4707
4708	=> bootm 40020000
4709	## Booting Linux kernel at 40020000 ...
4710	   Image Name:	 2.2.13 for NFS on TQM850L
4711	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4712	   Data Size:	 381681 Bytes = 372 kB = 0 MB
4713	   Load Address: 00000000
4714	   Entry Point:	 0000000c
4715	   Verifying Checksum ... OK
4716	   Uncompressing Kernel Image ... OK
4717	Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:35:17 MEST 2000
4718	Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
4719	time_init: decrementer frequency = 187500000/60
4720	Calibrating delay loop... 49.77 BogoMIPS
4721	Memory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000]
4722	...
4723
4724If you want to boot a Linux kernel with initial RAM disk, you pass
4725the memory addresses of both the kernel and the initrd image (PPBCOOT
4726format!) to the "bootm" command:
4727
4728	=> imi 40100000 40200000
4729
4730	## Checking Image at 40100000 ...
4731	   Image Name:	 2.2.13 for initrd on TQM850L
4732	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4733	   Data Size:	 335725 Bytes = 327 kB = 0 MB
4734	   Load Address: 00000000
4735	   Entry Point:	 0000000c
4736	   Verifying Checksum ... OK
4737
4738	## Checking Image at 40200000 ...
4739	   Image Name:	 Simple Ramdisk Image
4740	   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
4741	   Data Size:	 566530 Bytes = 553 kB = 0 MB
4742	   Load Address: 00000000
4743	   Entry Point:	 00000000
4744	   Verifying Checksum ... OK
4745
4746	=> bootm 40100000 40200000
4747	## Booting Linux kernel at 40100000 ...
4748	   Image Name:	 2.2.13 for initrd on TQM850L
4749	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4750	   Data Size:	 335725 Bytes = 327 kB = 0 MB
4751	   Load Address: 00000000
4752	   Entry Point:	 0000000c
4753	   Verifying Checksum ... OK
4754	   Uncompressing Kernel Image ... OK
4755	## Loading RAMDisk Image at 40200000 ...
4756	   Image Name:	 Simple Ramdisk Image
4757	   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
4758	   Data Size:	 566530 Bytes = 553 kB = 0 MB
4759	   Load Address: 00000000
4760	   Entry Point:	 00000000
4761	   Verifying Checksum ... OK
4762	   Loading Ramdisk ... OK
4763	Linux version 2.2.13 (wd@denx.local.net) (gcc version 2.95.2 19991024 (release)) #1 Wed Jul 19 02:32:08 MEST 2000
4764	Boot arguments: root=/dev/ram
4765	time_init: decrementer frequency = 187500000/60
4766	Calibrating delay loop... 49.77 BogoMIPS
4767	...
4768	RAMDISK: Compressed image found at block 0
4769	VFS: Mounted root (ext2 filesystem).
4770
4771	bash#
4772
4773Boot Linux and pass a flat device tree:
4774-----------
4775
4776First, U-Boot must be compiled with the appropriate defines. See the section
4777titled "Linux Kernel Interface" above for a more in depth explanation. The
4778following is an example of how to start a kernel and pass an updated
4779flat device tree:
4780
4781=> print oftaddr
4782oftaddr=0x300000
4783=> print oft
4784oft=oftrees/mpc8540ads.dtb
4785=> tftp $oftaddr $oft
4786Speed: 1000, full duplex
4787Using TSEC0 device
4788TFTP from server 192.168.1.1; our IP address is 192.168.1.101
4789Filename 'oftrees/mpc8540ads.dtb'.
4790Load address: 0x300000
4791Loading: #
4792done
4793Bytes transferred = 4106 (100a hex)
4794=> tftp $loadaddr $bootfile
4795Speed: 1000, full duplex
4796Using TSEC0 device
4797TFTP from server 192.168.1.1; our IP address is 192.168.1.2
4798Filename 'uImage'.
4799Load address: 0x200000
4800Loading:############
4801done
4802Bytes transferred = 1029407 (fb51f hex)
4803=> print loadaddr
4804loadaddr=200000
4805=> print oftaddr
4806oftaddr=0x300000
4807=> bootm $loadaddr - $oftaddr
4808## Booting image at 00200000 ...
4809   Image Name:	 Linux-2.6.17-dirty
4810   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4811   Data Size:	 1029343 Bytes = 1005.2 kB
4812   Load Address: 00000000
4813   Entry Point:	 00000000
4814   Verifying Checksum ... OK
4815   Uncompressing Kernel Image ... OK
4816Booting using flat device tree at 0x300000
4817Using MPC85xx ADS machine description
4818Memory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb
4819[snip]
4820
4821
4822More About U-Boot Image Types:
4823------------------------------
4824
4825U-Boot supports the following image types:
4826
4827   "Standalone Programs" are directly runnable in the environment
4828	provided by U-Boot; it is expected that (if they behave
4829	well) you can continue to work in U-Boot after return from
4830	the Standalone Program.
4831   "OS Kernel Images" are usually images of some Embedded OS which
4832	will take over control completely. Usually these programs
4833	will install their own set of exception handlers, device
4834	drivers, set up the MMU, etc. - this means, that you cannot
4835	expect to re-enter U-Boot except by resetting the CPU.
4836   "RAMDisk Images" are more or less just data blocks, and their
4837	parameters (address, size) are passed to an OS kernel that is
4838	being started.
4839   "Multi-File Images" contain several images, typically an OS
4840	(Linux) kernel image and one or more data images like
4841	RAMDisks. This construct is useful for instance when you want
4842	to boot over the network using BOOTP etc., where the boot
4843	server provides just a single image file, but you want to get
4844	for instance an OS kernel and a RAMDisk image.
4845
4846	"Multi-File Images" start with a list of image sizes, each
4847	image size (in bytes) specified by an "uint32_t" in network
4848	byte order. This list is terminated by an "(uint32_t)0".
4849	Immediately after the terminating 0 follow the images, one by
4850	one, all aligned on "uint32_t" boundaries (size rounded up to
4851	a multiple of 4 bytes).
4852
4853   "Firmware Images" are binary images containing firmware (like
4854	U-Boot or FPGA images) which usually will be programmed to
4855	flash memory.
4856
4857   "Script files" are command sequences that will be executed by
4858	U-Boot's command interpreter; this feature is especially
4859	useful when you configure U-Boot to use a real shell (hush)
4860	as command interpreter.
4861
4862Booting the Linux zImage:
4863-------------------------
4864
4865On some platforms, it's possible to boot Linux zImage. This is done
4866using the "bootz" command. The syntax of "bootz" command is the same
4867as the syntax of "bootm" command.
4868
4869Note, defining the CONFIG_SUPPORT_RAW_INITRD allows user to supply
4870kernel with raw initrd images. The syntax is slightly different, the
4871address of the initrd must be augmented by it's size, in the following
4872format: "<initrd addres>:<initrd size>".
4873
4874
4875Standalone HOWTO:
4876=================
4877
4878One of the features of U-Boot is that you can dynamically load and
4879run "standalone" applications, which can use some resources of
4880U-Boot like console I/O functions or interrupt services.
4881
4882Two simple examples are included with the sources:
4883
4884"Hello World" Demo:
4885-------------------
4886
4887'examples/hello_world.c' contains a small "Hello World" Demo
4888application; it is automatically compiled when you build U-Boot.
4889It's configured to run at address 0x00040004, so you can play with it
4890like that:
4891
4892	=> loads
4893	## Ready for S-Record download ...
4894	~>examples/hello_world.srec
4895	1 2 3 4 5 6 7 8 9 10 11 ...
4896	[file transfer complete]
4897	[connected]
4898	## Start Addr = 0x00040004
4899
4900	=> go 40004 Hello World! This is a test.
4901	## Starting application at 0x00040004 ...
4902	Hello World
4903	argc = 7
4904	argv[0] = "40004"
4905	argv[1] = "Hello"
4906	argv[2] = "World!"
4907	argv[3] = "This"
4908	argv[4] = "is"
4909	argv[5] = "a"
4910	argv[6] = "test."
4911	argv[7] = "<NULL>"
4912	Hit any key to exit ...
4913
4914	## Application terminated, rc = 0x0
4915
4916Another example, which demonstrates how to register a CPM interrupt
4917handler with the U-Boot code, can be found in 'examples/timer.c'.
4918Here, a CPM timer is set up to generate an interrupt every second.
4919The interrupt service routine is trivial, just printing a '.'
4920character, but this is just a demo program. The application can be
4921controlled by the following keys:
4922
4923	? - print current values og the CPM Timer registers
4924	b - enable interrupts and start timer
4925	e - stop timer and disable interrupts
4926	q - quit application
4927
4928	=> loads
4929	## Ready for S-Record download ...
4930	~>examples/timer.srec
4931	1 2 3 4 5 6 7 8 9 10 11 ...
4932	[file transfer complete]
4933	[connected]
4934	## Start Addr = 0x00040004
4935
4936	=> go 40004
4937	## Starting application at 0x00040004 ...
4938	TIMERS=0xfff00980
4939	Using timer 1
4940	  tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0
4941
4942Hit 'b':
4943	[q, b, e, ?] Set interval 1000000 us
4944	Enabling timer
4945Hit '?':
4946	[q, b, e, ?] ........
4947	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0
4948Hit '?':
4949	[q, b, e, ?] .
4950	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0
4951Hit '?':
4952	[q, b, e, ?] .
4953	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0
4954Hit '?':
4955	[q, b, e, ?] .
4956	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0
4957Hit 'e':
4958	[q, b, e, ?] ...Stopping timer
4959Hit 'q':
4960	[q, b, e, ?] ## Application terminated, rc = 0x0
4961
4962
4963Minicom warning:
4964================
4965
4966Over time, many people have reported problems when trying to use the
4967"minicom" terminal emulation program for serial download. I (wd)
4968consider minicom to be broken, and recommend not to use it. Under
4969Unix, I recommend to use C-Kermit for general purpose use (and
4970especially for kermit binary protocol download ("loadb" command), and
4971use "cu" for S-Record download ("loads" command).  See
4972http://www.denx.de/wiki/view/DULG/SystemSetup#Section_4.3.
4973for help with kermit.
4974
4975
4976Nevertheless, if you absolutely want to use it try adding this
4977configuration to your "File transfer protocols" section:
4978
4979	   Name	   Program			Name U/D FullScr IO-Red. Multi
4980	X  kermit  /usr/bin/kermit -i -l %l -s	 Y    U	   Y	   N	  N
4981	Y  kermit  /usr/bin/kermit -i -l %l -r	 N    D	   Y	   N	  N
4982
4983
4984NetBSD Notes:
4985=============
4986
4987Starting at version 0.9.2, U-Boot supports NetBSD both as host
4988(build U-Boot) and target system (boots NetBSD/mpc8xx).
4989
4990Building requires a cross environment; it is known to work on
4991NetBSD/i386 with the cross-powerpc-netbsd-1.3 package (you will also
4992need gmake since the Makefiles are not compatible with BSD make).
4993Note that the cross-powerpc package does not install include files;
4994attempting to build U-Boot will fail because <machine/ansi.h> is
4995missing.  This file has to be installed and patched manually:
4996
4997	# cd /usr/pkg/cross/powerpc-netbsd/include
4998	# mkdir powerpc
4999	# ln -s powerpc machine
5000	# cp /usr/src/sys/arch/powerpc/include/ansi.h powerpc/ansi.h
5001	# ${EDIT} powerpc/ansi.h	## must remove __va_list, _BSD_VA_LIST
5002
5003Native builds *don't* work due to incompatibilities between native
5004and U-Boot include files.
5005
5006Booting assumes that (the first part of) the image booted is a
5007stage-2 loader which in turn loads and then invokes the kernel
5008proper. Loader sources will eventually appear in the NetBSD source
5009tree (probably in sys/arc/mpc8xx/stand/u-boot_stage2/); in the
5010meantime, see ftp://ftp.denx.de/pub/u-boot/ppcboot_stage2.tar.gz
5011
5012
5013Implementation Internals:
5014=========================
5015
5016The following is not intended to be a complete description of every
5017implementation detail. However, it should help to understand the
5018inner workings of U-Boot and make it easier to port it to custom
5019hardware.
5020
5021
5022Initial Stack, Global Data:
5023---------------------------
5024
5025The implementation of U-Boot is complicated by the fact that U-Boot
5026starts running out of ROM (flash memory), usually without access to
5027system RAM (because the memory controller is not initialized yet).
5028This means that we don't have writable Data or BSS segments, and BSS
5029is not initialized as zero. To be able to get a C environment working
5030at all, we have to allocate at least a minimal stack. Implementation
5031options for this are defined and restricted by the CPU used: Some CPU
5032models provide on-chip memory (like the IMMR area on MPC8xx and
5033MPC826x processors), on others (parts of) the data cache can be
5034locked as (mis-) used as memory, etc.
5035
5036	Chris Hallinan posted a good summary of these issues to the
5037	U-Boot mailing list:
5038
5039	Subject: RE: [U-Boot-Users] RE: More On Memory Bank x (nothingness)?
5040	From: "Chris Hallinan" <clh@net1plus.com>
5041	Date: Mon, 10 Feb 2003 16:43:46 -0500 (22:43 MET)
5042	...
5043
5044	Correct me if I'm wrong, folks, but the way I understand it
5045	is this: Using DCACHE as initial RAM for Stack, etc, does not
5046	require any physical RAM backing up the cache. The cleverness
5047	is that the cache is being used as a temporary supply of
5048	necessary storage before the SDRAM controller is setup. It's
5049	beyond the scope of this list to explain the details, but you
5050	can see how this works by studying the cache architecture and
5051	operation in the architecture and processor-specific manuals.
5052
5053	OCM is On Chip Memory, which I believe the 405GP has 4K. It
5054	is another option for the system designer to use as an
5055	initial stack/RAM area prior to SDRAM being available. Either
5056	option should work for you. Using CS 4 should be fine if your
5057	board designers haven't used it for something that would
5058	cause you grief during the initial boot! It is frequently not
5059	used.
5060
5061	CONFIG_SYS_INIT_RAM_ADDR should be somewhere that won't interfere
5062	with your processor/board/system design. The default value
5063	you will find in any recent u-boot distribution in
5064	walnut.h should work for you. I'd set it to a value larger
5065	than your SDRAM module. If you have a 64MB SDRAM module, set
5066	it above 400_0000. Just make sure your board has no resources
5067	that are supposed to respond to that address! That code in
5068	start.S has been around a while and should work as is when
5069	you get the config right.
5070
5071	-Chris Hallinan
5072	DS4.COM, Inc.
5073
5074It is essential to remember this, since it has some impact on the C
5075code for the initialization procedures:
5076
5077* Initialized global data (data segment) is read-only. Do not attempt
5078  to write it.
5079
5080* Do not use any uninitialized global data (or implicitly initialized
5081  as zero data - BSS segment) at all - this is undefined, initiali-
5082  zation is performed later (when relocating to RAM).
5083
5084* Stack space is very limited. Avoid big data buffers or things like
5085  that.
5086
5087Having only the stack as writable memory limits means we cannot use
5088normal global data to share information between the code. But it
5089turned out that the implementation of U-Boot can be greatly
5090simplified by making a global data structure (gd_t) available to all
5091functions. We could pass a pointer to this data as argument to _all_
5092functions, but this would bloat the code. Instead we use a feature of
5093the GCC compiler (Global Register Variables) to share the data: we
5094place a pointer (gd) to the global data into a register which we
5095reserve for this purpose.
5096
5097When choosing a register for such a purpose we are restricted by the
5098relevant  (E)ABI  specifications for the current architecture, and by
5099GCC's implementation.
5100
5101For PowerPC, the following registers have specific use:
5102	R1:	stack pointer
5103	R2:	reserved for system use
5104	R3-R4:	parameter passing and return values
5105	R5-R10: parameter passing
5106	R13:	small data area pointer
5107	R30:	GOT pointer
5108	R31:	frame pointer
5109
5110	(U-Boot also uses R12 as internal GOT pointer. r12
5111	is a volatile register so r12 needs to be reset when
5112	going back and forth between asm and C)
5113
5114    ==> U-Boot will use R2 to hold a pointer to the global data
5115
5116    Note: on PPC, we could use a static initializer (since the
5117    address of the global data structure is known at compile time),
5118    but it turned out that reserving a register results in somewhat
5119    smaller code - although the code savings are not that big (on
5120    average for all boards 752 bytes for the whole U-Boot image,
5121    624 text + 127 data).
5122
5123On ARM, the following registers are used:
5124
5125	R0:	function argument word/integer result
5126	R1-R3:	function argument word
5127	R9:	platform specific
5128	R10:	stack limit (used only if stack checking is enabled)
5129	R11:	argument (frame) pointer
5130	R12:	temporary workspace
5131	R13:	stack pointer
5132	R14:	link register
5133	R15:	program counter
5134
5135    ==> U-Boot will use R9 to hold a pointer to the global data
5136
5137    Note: on ARM, only R_ARM_RELATIVE relocations are supported.
5138
5139On Nios II, the ABI is documented here:
5140	http://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf
5141
5142    ==> U-Boot will use gp to hold a pointer to the global data
5143
5144    Note: on Nios II, we give "-G0" option to gcc and don't use gp
5145    to access small data sections, so gp is free.
5146
5147On NDS32, the following registers are used:
5148
5149	R0-R1:	argument/return
5150	R2-R5:	argument
5151	R15:	temporary register for assembler
5152	R16:	trampoline register
5153	R28:	frame pointer (FP)
5154	R29:	global pointer (GP)
5155	R30:	link register (LP)
5156	R31:	stack pointer (SP)
5157	PC:	program counter (PC)
5158
5159    ==> U-Boot will use R10 to hold a pointer to the global data
5160
5161NOTE: DECLARE_GLOBAL_DATA_PTR must be used with file-global scope,
5162or current versions of GCC may "optimize" the code too much.
5163
5164Memory Management:
5165------------------
5166
5167U-Boot runs in system state and uses physical addresses, i.e. the
5168MMU is not used either for address mapping nor for memory protection.
5169
5170The available memory is mapped to fixed addresses using the memory
5171controller. In this process, a contiguous block is formed for each
5172memory type (Flash, SDRAM, SRAM), even when it consists of several
5173physical memory banks.
5174
5175U-Boot is installed in the first 128 kB of the first Flash bank (on
5176TQM8xxL modules this is the range 0x40000000 ... 0x4001FFFF). After
5177booting and sizing and initializing DRAM, the code relocates itself
5178to the upper end of DRAM. Immediately below the U-Boot code some
5179memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
5180configuration setting]. Below that, a structure with global Board
5181Info data is placed, followed by the stack (growing downward).
5182
5183Additionally, some exception handler code is copied to the low 8 kB
5184of DRAM (0x00000000 ... 0x00001FFF).
5185
5186So a typical memory configuration with 16 MB of DRAM could look like
5187this:
5188
5189	0x0000 0000	Exception Vector code
5190	      :
5191	0x0000 1FFF
5192	0x0000 2000	Free for Application Use
5193	      :
5194	      :
5195
5196	      :
5197	      :
5198	0x00FB FF20	Monitor Stack (Growing downward)
5199	0x00FB FFAC	Board Info Data and permanent copy of global data
5200	0x00FC 0000	Malloc Arena
5201	      :
5202	0x00FD FFFF
5203	0x00FE 0000	RAM Copy of Monitor Code
5204	...		eventually: LCD or video framebuffer
5205	...		eventually: pRAM (Protected RAM - unchanged by reset)
5206	0x00FF FFFF	[End of RAM]
5207
5208
5209System Initialization:
5210----------------------
5211
5212In the reset configuration, U-Boot starts at the reset entry point
5213(on most PowerPC systems at address 0x00000100). Because of the reset
5214configuration for CS0# this is a mirror of the on board Flash memory.
5215To be able to re-map memory U-Boot then jumps to its link address.
5216To be able to implement the initialization code in C, a (small!)
5217initial stack is set up in the internal Dual Ported RAM (in case CPUs
5218which provide such a feature like), or in a locked part of the data
5219cache. After that, U-Boot initializes the CPU core, the caches and
5220the SIU.
5221
5222Next, all (potentially) available memory banks are mapped using a
5223preliminary mapping. For example, we put them on 512 MB boundaries
5224(multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flash
5225on 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A is
5226programmed for SDRAM access. Using the temporary configuration, a
5227simple memory test is run that determines the size of the SDRAM
5228banks.
5229
5230When there is more than one SDRAM bank, and the banks are of
5231different size, the largest is mapped first. For equal size, the first
5232bank (CS2#) is mapped first. The first mapping is always for address
52330x00000000, with any additional banks following immediately to create
5234contiguous memory starting from 0.
5235
5236Then, the monitor installs itself at the upper end of the SDRAM area
5237and allocates memory for use by malloc() and for the global Board
5238Info data; also, the exception vector code is copied to the low RAM
5239pages, and the final stack is set up.
5240
5241Only after this relocation will you have a "normal" C environment;
5242until that you are restricted in several ways, mostly because you are
5243running from ROM, and because the code will have to be relocated to a
5244new address in RAM.
5245
5246
5247U-Boot Porting Guide:
5248----------------------
5249
5250[Based on messages by Jerry Van Baren in the U-Boot-Users mailing
5251list, October 2002]
5252
5253
5254int main(int argc, char *argv[])
5255{
5256	sighandler_t no_more_time;
5257
5258	signal(SIGALRM, no_more_time);
5259	alarm(PROJECT_DEADLINE - toSec (3 * WEEK));
5260
5261	if (available_money > available_manpower) {
5262		Pay consultant to port U-Boot;
5263		return 0;
5264	}
5265
5266	Download latest U-Boot source;
5267
5268	Subscribe to u-boot mailing list;
5269
5270	if (clueless)
5271		email("Hi, I am new to U-Boot, how do I get started?");
5272
5273	while (learning) {
5274		Read the README file in the top level directory;
5275		Read http://www.denx.de/twiki/bin/view/DULG/Manual;
5276		Read applicable doc/*.README;
5277		Read the source, Luke;
5278		/* find . -name "*.[chS]" | xargs grep -i <keyword> */
5279	}
5280
5281	if (available_money > toLocalCurrency ($2500))
5282		Buy a BDI3000;
5283	else
5284		Add a lot of aggravation and time;
5285
5286	if (a similar board exists) {	/* hopefully... */
5287		cp -a board/<similar> board/<myboard>
5288		cp include/configs/<similar>.h include/configs/<myboard>.h
5289	} else {
5290		Create your own board support subdirectory;
5291		Create your own board include/configs/<myboard>.h file;
5292	}
5293	Edit new board/<myboard> files
5294	Edit new include/configs/<myboard>.h
5295
5296	while (!accepted) {
5297		while (!running) {
5298			do {
5299				Add / modify source code;
5300			} until (compiles);
5301			Debug;
5302			if (clueless)
5303				email("Hi, I am having problems...");
5304		}
5305		Send patch file to the U-Boot email list;
5306		if (reasonable critiques)
5307			Incorporate improvements from email list code review;
5308		else
5309			Defend code as written;
5310	}
5311
5312	return 0;
5313}
5314
5315void no_more_time (int sig)
5316{
5317      hire_a_guru();
5318}
5319
5320
5321Coding Standards:
5322-----------------
5323
5324All contributions to U-Boot should conform to the Linux kernel
5325coding style; see the file "Documentation/CodingStyle" and the script
5326"scripts/Lindent" in your Linux kernel source directory.
5327
5328Source files originating from a different project (for example the
5329MTD subsystem) are generally exempt from these guidelines and are not
5330reformatted to ease subsequent migration to newer versions of those
5331sources.
5332
5333Please note that U-Boot is implemented in C (and to some small parts in
5334Assembler); no C++ is used, so please do not use C++ style comments (//)
5335in your code.
5336
5337Please also stick to the following formatting rules:
5338- remove any trailing white space
5339- use TAB characters for indentation and vertical alignment, not spaces
5340- make sure NOT to use DOS '\r\n' line feeds
5341- do not add more than 2 consecutive empty lines to source files
5342- do not add trailing empty lines to source files
5343
5344Submissions which do not conform to the standards may be returned
5345with a request to reformat the changes.
5346
5347
5348Submitting Patches:
5349-------------------
5350
5351Since the number of patches for U-Boot is growing, we need to
5352establish some rules. Submissions which do not conform to these rules
5353may be rejected, even when they contain important and valuable stuff.
5354
5355Please see http://www.denx.de/wiki/U-Boot/Patches for details.
5356
5357Patches shall be sent to the u-boot mailing list <u-boot@lists.denx.de>;
5358see http://lists.denx.de/mailman/listinfo/u-boot
5359
5360When you send a patch, please include the following information with
5361it:
5362
5363* For bug fixes: a description of the bug and how your patch fixes
5364  this bug. Please try to include a way of demonstrating that the
5365  patch actually fixes something.
5366
5367* For new features: a description of the feature and your
5368  implementation.
5369
5370* A CHANGELOG entry as plaintext (separate from the patch)
5371
5372* For major contributions, add a MAINTAINERS file with your
5373  information and associated file and directory references.
5374
5375* When you add support for a new board, don't forget to add a
5376  maintainer e-mail address to the boards.cfg file, too.
5377
5378* If your patch adds new configuration options, don't forget to
5379  document these in the README file.
5380
5381* The patch itself. If you are using git (which is *strongly*
5382  recommended) you can easily generate the patch using the
5383  "git format-patch". If you then use "git send-email" to send it to
5384  the U-Boot mailing list, you will avoid most of the common problems
5385  with some other mail clients.
5386
5387  If you cannot use git, use "diff -purN OLD NEW". If your version of
5388  diff does not support these options, then get the latest version of
5389  GNU diff.
5390
5391  The current directory when running this command shall be the parent
5392  directory of the U-Boot source tree (i. e. please make sure that
5393  your patch includes sufficient directory information for the
5394  affected files).
5395
5396  We prefer patches as plain text. MIME attachments are discouraged,
5397  and compressed attachments must not be used.
5398
5399* If one logical set of modifications affects or creates several
5400  files, all these changes shall be submitted in a SINGLE patch file.
5401
5402* Changesets that contain different, unrelated modifications shall be
5403  submitted as SEPARATE patches, one patch per changeset.
5404
5405
5406Notes:
5407
5408* Before sending the patch, run the buildman script on your patched
5409  source tree and make sure that no errors or warnings are reported
5410  for any of the boards.
5411
5412* Keep your modifications to the necessary minimum: A patch
5413  containing several unrelated changes or arbitrary reformats will be
5414  returned with a request to re-formatting / split it.
5415
5416* If you modify existing code, make sure that your new code does not
5417  add to the memory footprint of the code ;-) Small is beautiful!
5418  When adding new features, these should compile conditionally only
5419  (using #ifdef), and the resulting code with the new feature
5420  disabled must not need more memory than the old code without your
5421  modification.
5422
5423* Remember that there is a size limit of 100 kB per message on the
5424  u-boot mailing list. Bigger patches will be moderated. If they are
5425  reasonable and not too big, they will be acknowledged. But patches
5426  bigger than the size limit should be avoided.
5427