xref: /openbmc/u-boot/README (revision 8f6d5bbb)
1# SPDX-License-Identifier: GPL-2.0+
2#
3# (C) Copyright 2000 - 2013
4# Wolfgang Denk, DENX Software Engineering, wd@denx.de.
5
6Summary:
7========
8
9This directory contains the source code for U-Boot, a boot loader for
10Embedded boards based on PowerPC, ARM, MIPS and several other
11processors, which can be installed in a boot ROM and used to
12initialize and test the hardware or to download and run application
13code.
14
15The development of U-Boot is closely related to Linux: some parts of
16the source code originate in the Linux source tree, we have some
17header files in common, and special provision has been made to
18support booting of Linux images.
19
20Some attention has been paid to make this software easily
21configurable and extendable. For instance, all monitor commands are
22implemented with the same call interface, so that it's very easy to
23add new commands. Also, instead of permanently adding rarely used
24code (for instance hardware test utilities) to the monitor, you can
25load and run it dynamically.
26
27
28Status:
29=======
30
31In general, all boards for which a configuration option exists in the
32Makefile have been tested to some extent and can be considered
33"working". In fact, many of them are used in production systems.
34
35In case of problems see the CHANGELOG file to find out who contributed
36the specific port. In addition, there are various MAINTAINERS files
37scattered throughout the U-Boot source identifying the people or
38companies responsible for various boards and subsystems.
39
40Note: As of August, 2010, there is no longer a CHANGELOG file in the
41actual U-Boot source tree; however, it can be created dynamically
42from the Git log using:
43
44	make CHANGELOG
45
46
47Where to get help:
48==================
49
50In case you have questions about, problems with or contributions for
51U-Boot, you should send a message to the U-Boot mailing list at
52<u-boot@lists.denx.de>. There is also an archive of previous traffic
53on the mailing list - please search the archive before asking FAQ's.
54Please see http://lists.denx.de/pipermail/u-boot and
55http://dir.gmane.org/gmane.comp.boot-loaders.u-boot
56
57
58Where to get source code:
59=========================
60
61The U-Boot source code is maintained in the Git repository at
62git://www.denx.de/git/u-boot.git ; you can browse it online at
63http://www.denx.de/cgi-bin/gitweb.cgi?p=u-boot.git;a=summary
64
65The "snapshot" links on this page allow you to download tarballs of
66any version you might be interested in. Official releases are also
67available for FTP download from the ftp://ftp.denx.de/pub/u-boot/
68directory.
69
70Pre-built (and tested) images are available from
71ftp://ftp.denx.de/pub/u-boot/images/
72
73
74Where we come from:
75===================
76
77- start from 8xxrom sources
78- create PPCBoot project (http://sourceforge.net/projects/ppcboot)
79- clean up code
80- make it easier to add custom boards
81- make it possible to add other [PowerPC] CPUs
82- extend functions, especially:
83  * Provide extended interface to Linux boot loader
84  * S-Record download
85  * network boot
86  * PCMCIA / CompactFlash / ATA disk / SCSI ... boot
87- create ARMBoot project (http://sourceforge.net/projects/armboot)
88- add other CPU families (starting with ARM)
89- create U-Boot project (http://sourceforge.net/projects/u-boot)
90- current project page: see http://www.denx.de/wiki/U-Boot
91
92
93Names and Spelling:
94===================
95
96The "official" name of this project is "Das U-Boot". The spelling
97"U-Boot" shall be used in all written text (documentation, comments
98in source files etc.). Example:
99
100	This is the README file for the U-Boot project.
101
102File names etc. shall be based on the string "u-boot". Examples:
103
104	include/asm-ppc/u-boot.h
105
106	#include <asm/u-boot.h>
107
108Variable names, preprocessor constants etc. shall be either based on
109the string "u_boot" or on "U_BOOT". Example:
110
111	U_BOOT_VERSION		u_boot_logo
112	IH_OS_U_BOOT		u_boot_hush_start
113
114
115Versioning:
116===========
117
118Starting with the release in October 2008, the names of the releases
119were changed from numerical release numbers without deeper meaning
120into a time stamp based numbering. Regular releases are identified by
121names consisting of the calendar year and month of the release date.
122Additional fields (if present) indicate release candidates or bug fix
123releases in "stable" maintenance trees.
124
125Examples:
126	U-Boot v2009.11	    - Release November 2009
127	U-Boot v2009.11.1   - Release 1 in version November 2009 stable tree
128	U-Boot v2010.09-rc1 - Release candidate 1 for September 2010 release
129
130
131Directory Hierarchy:
132====================
133
134/arch			Architecture specific files
135  /arc			Files generic to ARC architecture
136  /arm			Files generic to ARM architecture
137  /m68k			Files generic to m68k architecture
138  /microblaze		Files generic to microblaze architecture
139  /mips			Files generic to MIPS architecture
140  /nds32		Files generic to NDS32 architecture
141  /nios2		Files generic to Altera NIOS2 architecture
142  /openrisc		Files generic to OpenRISC architecture
143  /powerpc		Files generic to PowerPC architecture
144  /riscv		Files generic to RISC-V architecture
145  /sandbox		Files generic to HW-independent "sandbox"
146  /sh			Files generic to SH architecture
147  /x86			Files generic to x86 architecture
148/api			Machine/arch independent API for external apps
149/board			Board dependent files
150/cmd			U-Boot commands functions
151/common			Misc architecture independent functions
152/configs		Board default configuration files
153/disk			Code for disk drive partition handling
154/doc			Documentation (don't expect too much)
155/drivers		Commonly used device drivers
156/dts			Contains Makefile for building internal U-Boot fdt.
157/examples		Example code for standalone applications, etc.
158/fs			Filesystem code (cramfs, ext2, jffs2, etc.)
159/include		Header Files
160/lib			Library routines generic to all architectures
161/Licenses		Various license files
162/net			Networking code
163/post			Power On Self Test
164/scripts		Various build scripts and Makefiles
165/test			Various unit test files
166/tools			Tools to build S-Record or U-Boot images, etc.
167
168Software Configuration:
169=======================
170
171Configuration is usually done using C preprocessor defines; the
172rationale behind that is to avoid dead code whenever possible.
173
174There are two classes of configuration variables:
175
176* Configuration _OPTIONS_:
177  These are selectable by the user and have names beginning with
178  "CONFIG_".
179
180* Configuration _SETTINGS_:
181  These depend on the hardware etc. and should not be meddled with if
182  you don't know what you're doing; they have names beginning with
183  "CONFIG_SYS_".
184
185Previously, all configuration was done by hand, which involved creating
186symbolic links and editing configuration files manually. More recently,
187U-Boot has added the Kbuild infrastructure used by the Linux kernel,
188allowing you to use the "make menuconfig" command to configure your
189build.
190
191
192Selection of Processor Architecture and Board Type:
193---------------------------------------------------
194
195For all supported boards there are ready-to-use default
196configurations available; just type "make <board_name>_defconfig".
197
198Example: For a TQM823L module type:
199
200	cd u-boot
201	make TQM823L_defconfig
202
203Note: If you're looking for the default configuration file for a board
204you're sure used to be there but is now missing, check the file
205doc/README.scrapyard for a list of no longer supported boards.
206
207Sandbox Environment:
208--------------------
209
210U-Boot can be built natively to run on a Linux host using the 'sandbox'
211board. This allows feature development which is not board- or architecture-
212specific to be undertaken on a native platform. The sandbox is also used to
213run some of U-Boot's tests.
214
215See board/sandbox/README.sandbox for more details.
216
217
218Board Initialisation Flow:
219--------------------------
220
221This is the intended start-up flow for boards. This should apply for both
222SPL and U-Boot proper (i.e. they both follow the same rules).
223
224Note: "SPL" stands for "Secondary Program Loader," which is explained in
225more detail later in this file.
226
227At present, SPL mostly uses a separate code path, but the function names
228and roles of each function are the same. Some boards or architectures
229may not conform to this.  At least most ARM boards which use
230CONFIG_SPL_FRAMEWORK conform to this.
231
232Execution typically starts with an architecture-specific (and possibly
233CPU-specific) start.S file, such as:
234
235	- arch/arm/cpu/armv7/start.S
236	- arch/powerpc/cpu/mpc83xx/start.S
237	- arch/mips/cpu/start.S
238
239and so on. From there, three functions are called; the purpose and
240limitations of each of these functions are described below.
241
242lowlevel_init():
243	- purpose: essential init to permit execution to reach board_init_f()
244	- no global_data or BSS
245	- there is no stack (ARMv7 may have one but it will soon be removed)
246	- must not set up SDRAM or use console
247	- must only do the bare minimum to allow execution to continue to
248		board_init_f()
249	- this is almost never needed
250	- return normally from this function
251
252board_init_f():
253	- purpose: set up the machine ready for running board_init_r():
254		i.e. SDRAM and serial UART
255	- global_data is available
256	- stack is in SRAM
257	- BSS is not available, so you cannot use global/static variables,
258		only stack variables and global_data
259
260	Non-SPL-specific notes:
261	- dram_init() is called to set up DRAM. If already done in SPL this
262		can do nothing
263
264	SPL-specific notes:
265	- you can override the entire board_init_f() function with your own
266		version as needed.
267	- preloader_console_init() can be called here in extremis
268	- should set up SDRAM, and anything needed to make the UART work
269	- these is no need to clear BSS, it will be done by crt0.S
270	- must return normally from this function (don't call board_init_r()
271		directly)
272
273Here the BSS is cleared. For SPL, if CONFIG_SPL_STACK_R is defined, then at
274this point the stack and global_data are relocated to below
275CONFIG_SPL_STACK_R_ADDR. For non-SPL, U-Boot is relocated to run at the top of
276memory.
277
278board_init_r():
279	- purpose: main execution, common code
280	- global_data is available
281	- SDRAM is available
282	- BSS is available, all static/global variables can be used
283	- execution eventually continues to main_loop()
284
285	Non-SPL-specific notes:
286	- U-Boot is relocated to the top of memory and is now running from
287		there.
288
289	SPL-specific notes:
290	- stack is optionally in SDRAM, if CONFIG_SPL_STACK_R is defined and
291		CONFIG_SPL_STACK_R_ADDR points into SDRAM
292	- preloader_console_init() can be called here - typically this is
293		done by selecting CONFIG_SPL_BOARD_INIT and then supplying a
294		spl_board_init() function containing this call
295	- loads U-Boot or (in falcon mode) Linux
296
297
298
299Configuration Options:
300----------------------
301
302Configuration depends on the combination of board and CPU type; all
303such information is kept in a configuration file
304"include/configs/<board_name>.h".
305
306Example: For a TQM823L module, all configuration settings are in
307"include/configs/TQM823L.h".
308
309
310Many of the options are named exactly as the corresponding Linux
311kernel configuration options. The intention is to make it easier to
312build a config tool - later.
313
314- ARM Platform Bus Type(CCI):
315		CoreLink Cache Coherent Interconnect (CCI) is ARM BUS which
316		provides full cache coherency between two clusters of multi-core
317		CPUs and I/O coherency for devices and I/O masters
318
319		CONFIG_SYS_FSL_HAS_CCI400
320
321		Defined For SoC that has cache coherent interconnect
322		CCN-400
323
324		CONFIG_SYS_FSL_HAS_CCN504
325
326		Defined for SoC that has cache coherent interconnect CCN-504
327
328The following options need to be configured:
329
330- CPU Type:	Define exactly one, e.g. CONFIG_MPC85XX.
331
332- Board Type:	Define exactly one, e.g. CONFIG_MPC8540ADS.
333
334- 85xx CPU Options:
335		CONFIG_SYS_PPC64
336
337		Specifies that the core is a 64-bit PowerPC implementation (implements
338		the "64" category of the Power ISA). This is necessary for ePAPR
339		compliance, among other possible reasons.
340
341		CONFIG_SYS_FSL_TBCLK_DIV
342
343		Defines the core time base clock divider ratio compared to the
344		system clock.  On most PQ3 devices this is 8, on newer QorIQ
345		devices it can be 16 or 32.  The ratio varies from SoC to Soc.
346
347		CONFIG_SYS_FSL_PCIE_COMPAT
348
349		Defines the string to utilize when trying to match PCIe device
350		tree nodes for the given platform.
351
352		CONFIG_SYS_FSL_ERRATUM_A004510
353
354		Enables a workaround for erratum A004510.  If set,
355		then CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV and
356		CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY must be set.
357
358		CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV
359		CONFIG_SYS_FSL_ERRATUM_A004510_SVR_REV2 (optional)
360
361		Defines one or two SoC revisions (low 8 bits of SVR)
362		for which the A004510 workaround should be applied.
363
364		The rest of SVR is either not relevant to the decision
365		of whether the erratum is present (e.g. p2040 versus
366		p2041) or is implied by the build target, which controls
367		whether CONFIG_SYS_FSL_ERRATUM_A004510 is set.
368
369		See Freescale App Note 4493 for more information about
370		this erratum.
371
372		CONFIG_A003399_NOR_WORKAROUND
373		Enables a workaround for IFC erratum A003399. It is only
374		required during NOR boot.
375
376		CONFIG_A008044_WORKAROUND
377		Enables a workaround for T1040/T1042 erratum A008044. It is only
378		required during NAND boot and valid for Rev 1.0 SoC revision
379
380		CONFIG_SYS_FSL_CORENET_SNOOPVEC_COREONLY
381
382		This is the value to write into CCSR offset 0x18600
383		according to the A004510 workaround.
384
385		CONFIG_SYS_FSL_DSP_DDR_ADDR
386		This value denotes start offset of DDR memory which is
387		connected exclusively to the DSP cores.
388
389		CONFIG_SYS_FSL_DSP_M2_RAM_ADDR
390		This value denotes start offset of M2 memory
391		which is directly connected to the DSP core.
392
393		CONFIG_SYS_FSL_DSP_M3_RAM_ADDR
394		This value denotes start offset of M3 memory which is directly
395		connected to the DSP core.
396
397		CONFIG_SYS_FSL_DSP_CCSRBAR_DEFAULT
398		This value denotes start offset of DSP CCSR space.
399
400		CONFIG_SYS_FSL_SINGLE_SOURCE_CLK
401		Single Source Clock is clocking mode present in some of FSL SoC's.
402		In this mode, a single differential clock is used to supply
403		clocks to the sysclock, ddrclock and usbclock.
404
405		CONFIG_SYS_CPC_REINIT_F
406		This CONFIG is defined when the CPC is configured as SRAM at the
407		time of U-Boot entry and is required to be re-initialized.
408
409		CONFIG_DEEP_SLEEP
410		Indicates this SoC supports deep sleep feature. If deep sleep is
411		supported, core will start to execute uboot when wakes up.
412
413- Generic CPU options:
414		CONFIG_SYS_BIG_ENDIAN, CONFIG_SYS_LITTLE_ENDIAN
415
416		Defines the endianess of the CPU. Implementation of those
417		values is arch specific.
418
419		CONFIG_SYS_FSL_DDR
420		Freescale DDR driver in use. This type of DDR controller is
421		found in mpc83xx, mpc85xx, mpc86xx as well as some ARM core
422		SoCs.
423
424		CONFIG_SYS_FSL_DDR_ADDR
425		Freescale DDR memory-mapped register base.
426
427		CONFIG_SYS_FSL_DDR_EMU
428		Specify emulator support for DDR. Some DDR features such as
429		deskew training are not available.
430
431		CONFIG_SYS_FSL_DDRC_GEN1
432		Freescale DDR1 controller.
433
434		CONFIG_SYS_FSL_DDRC_GEN2
435		Freescale DDR2 controller.
436
437		CONFIG_SYS_FSL_DDRC_GEN3
438		Freescale DDR3 controller.
439
440		CONFIG_SYS_FSL_DDRC_GEN4
441		Freescale DDR4 controller.
442
443		CONFIG_SYS_FSL_DDRC_ARM_GEN3
444		Freescale DDR3 controller for ARM-based SoCs.
445
446		CONFIG_SYS_FSL_DDR1
447		Board config to use DDR1. It can be enabled for SoCs with
448		Freescale DDR1 or DDR2 controllers, depending on the board
449		implemetation.
450
451		CONFIG_SYS_FSL_DDR2
452		Board config to use DDR2. It can be enabled for SoCs with
453		Freescale DDR2 or DDR3 controllers, depending on the board
454		implementation.
455
456		CONFIG_SYS_FSL_DDR3
457		Board config to use DDR3. It can be enabled for SoCs with
458		Freescale DDR3 or DDR3L controllers.
459
460		CONFIG_SYS_FSL_DDR3L
461		Board config to use DDR3L. It can be enabled for SoCs with
462		DDR3L controllers.
463
464		CONFIG_SYS_FSL_DDR4
465		Board config to use DDR4. It can be enabled for SoCs with
466		DDR4 controllers.
467
468		CONFIG_SYS_FSL_IFC_BE
469		Defines the IFC controller register space as Big Endian
470
471		CONFIG_SYS_FSL_IFC_LE
472		Defines the IFC controller register space as Little Endian
473
474		CONFIG_SYS_FSL_IFC_CLK_DIV
475		Defines divider of platform clock(clock input to IFC controller).
476
477		CONFIG_SYS_FSL_LBC_CLK_DIV
478		Defines divider of platform clock(clock input to eLBC controller).
479
480		CONFIG_SYS_FSL_PBL_PBI
481		It enables addition of RCW (Power on reset configuration) in built image.
482		Please refer doc/README.pblimage for more details
483
484		CONFIG_SYS_FSL_PBL_RCW
485		It adds PBI(pre-boot instructions) commands in u-boot build image.
486		PBI commands can be used to configure SoC before it starts the execution.
487		Please refer doc/README.pblimage for more details
488
489		CONFIG_SPL_FSL_PBL
490		It adds a target to create boot binary having SPL binary in PBI format
491		concatenated with u-boot binary.
492
493		CONFIG_SYS_FSL_DDR_BE
494		Defines the DDR controller register space as Big Endian
495
496		CONFIG_SYS_FSL_DDR_LE
497		Defines the DDR controller register space as Little Endian
498
499		CONFIG_SYS_FSL_DDR_SDRAM_BASE_PHY
500		Physical address from the view of DDR controllers. It is the
501		same as CONFIG_SYS_DDR_SDRAM_BASE for  all Power SoCs. But
502		it could be different for ARM SoCs.
503
504		CONFIG_SYS_FSL_DDR_INTLV_256B
505		DDR controller interleaving on 256-byte. This is a special
506		interleaving mode, handled by Dickens for Freescale layerscape
507		SoCs with ARM core.
508
509		CONFIG_SYS_FSL_DDR_MAIN_NUM_CTRLS
510		Number of controllers used as main memory.
511
512		CONFIG_SYS_FSL_OTHER_DDR_NUM_CTRLS
513		Number of controllers used for other than main memory.
514
515		CONFIG_SYS_FSL_HAS_DP_DDR
516		Defines the SoC has DP-DDR used for DPAA.
517
518		CONFIG_SYS_FSL_SEC_BE
519		Defines the SEC controller register space as Big Endian
520
521		CONFIG_SYS_FSL_SEC_LE
522		Defines the SEC controller register space as Little Endian
523
524- MIPS CPU options:
525		CONFIG_SYS_INIT_SP_OFFSET
526
527		Offset relative to CONFIG_SYS_SDRAM_BASE for initial stack
528		pointer. This is needed for the temporary stack before
529		relocation.
530
531		CONFIG_XWAY_SWAP_BYTES
532
533		Enable compilation of tools/xway-swap-bytes needed for Lantiq
534		XWAY SoCs for booting from NOR flash. The U-Boot image needs to
535		be swapped if a flash programmer is used.
536
537- ARM options:
538		CONFIG_SYS_EXCEPTION_VECTORS_HIGH
539
540		Select high exception vectors of the ARM core, e.g., do not
541		clear the V bit of the c1 register of CP15.
542
543		COUNTER_FREQUENCY
544		Generic timer clock source frequency.
545
546		COUNTER_FREQUENCY_REAL
547		Generic timer clock source frequency if the real clock is
548		different from COUNTER_FREQUENCY, and can only be determined
549		at run time.
550
551- Tegra SoC options:
552		CONFIG_TEGRA_SUPPORT_NON_SECURE
553
554		Support executing U-Boot in non-secure (NS) mode. Certain
555		impossible actions will be skipped if the CPU is in NS mode,
556		such as ARM architectural timer initialization.
557
558- Linux Kernel Interface:
559		CONFIG_CLOCKS_IN_MHZ
560
561		U-Boot stores all clock information in Hz
562		internally. For binary compatibility with older Linux
563		kernels (which expect the clocks passed in the
564		bd_info data to be in MHz) the environment variable
565		"clocks_in_mhz" can be defined so that U-Boot
566		converts clock data to MHZ before passing it to the
567		Linux kernel.
568		When CONFIG_CLOCKS_IN_MHZ is defined, a definition of
569		"clocks_in_mhz=1" is automatically included in the
570		default environment.
571
572		CONFIG_MEMSIZE_IN_BYTES		[relevant for MIPS only]
573
574		When transferring memsize parameter to Linux, some versions
575		expect it to be in bytes, others in MB.
576		Define CONFIG_MEMSIZE_IN_BYTES to make it in bytes.
577
578		CONFIG_OF_LIBFDT
579
580		New kernel versions are expecting firmware settings to be
581		passed using flattened device trees (based on open firmware
582		concepts).
583
584		CONFIG_OF_LIBFDT
585		 * New libfdt-based support
586		 * Adds the "fdt" command
587		 * The bootm command automatically updates the fdt
588
589		OF_TBCLK - The timebase frequency.
590		OF_STDOUT_PATH - The path to the console device
591
592		boards with QUICC Engines require OF_QE to set UCC MAC
593		addresses
594
595		CONFIG_OF_BOARD_SETUP
596
597		Board code has addition modification that it wants to make
598		to the flat device tree before handing it off to the kernel
599
600		CONFIG_OF_SYSTEM_SETUP
601
602		Other code has addition modification that it wants to make
603		to the flat device tree before handing it off to the kernel.
604		This causes ft_system_setup() to be called before booting
605		the kernel.
606
607		CONFIG_OF_IDE_FIXUP
608
609		U-Boot can detect if an IDE device is present or not.
610		If not, and this new config option is activated, U-Boot
611		removes the ATA node from the DTS before booting Linux,
612		so the Linux IDE driver does not probe the device and
613		crash. This is needed for buggy hardware (uc101) where
614		no pull down resistor is connected to the signal IDE5V_DD7.
615
616		CONFIG_MACH_TYPE	[relevant for ARM only][mandatory]
617
618		This setting is mandatory for all boards that have only one
619		machine type and must be used to specify the machine type
620		number as it appears in the ARM machine registry
621		(see http://www.arm.linux.org.uk/developer/machines/).
622		Only boards that have multiple machine types supported
623		in a single configuration file and the machine type is
624		runtime discoverable, do not have to use this setting.
625
626- vxWorks boot parameters:
627
628		bootvx constructs a valid bootline using the following
629		environments variables: bootdev, bootfile, ipaddr, netmask,
630		serverip, gatewayip, hostname, othbootargs.
631		It loads the vxWorks image pointed bootfile.
632
633		Note: If a "bootargs" environment is defined, it will overwride
634		the defaults discussed just above.
635
636- Cache Configuration:
637		CONFIG_SYS_ICACHE_OFF - Do not enable instruction cache in U-Boot
638		CONFIG_SYS_DCACHE_OFF - Do not enable data cache in U-Boot
639		CONFIG_SYS_L2CACHE_OFF- Do not enable L2 cache in U-Boot
640
641- Cache Configuration for ARM:
642		CONFIG_SYS_L2_PL310 - Enable support for ARM PL310 L2 cache
643				      controller
644		CONFIG_SYS_PL310_BASE - Physical base address of PL310
645					controller register space
646
647- Serial Ports:
648		CONFIG_PL010_SERIAL
649
650		Define this if you want support for Amba PrimeCell PL010 UARTs.
651
652		CONFIG_PL011_SERIAL
653
654		Define this if you want support for Amba PrimeCell PL011 UARTs.
655
656		CONFIG_PL011_CLOCK
657
658		If you have Amba PrimeCell PL011 UARTs, set this variable to
659		the clock speed of the UARTs.
660
661		CONFIG_PL01x_PORTS
662
663		If you have Amba PrimeCell PL010 or PL011 UARTs on your board,
664		define this to a list of base addresses for each (supported)
665		port. See e.g. include/configs/versatile.h
666
667		CONFIG_SERIAL_HW_FLOW_CONTROL
668
669		Define this variable to enable hw flow control in serial driver.
670		Current user of this option is drivers/serial/nsl16550.c driver
671
672- Console Baudrate:
673		CONFIG_BAUDRATE - in bps
674		Select one of the baudrates listed in
675		CONFIG_SYS_BAUDRATE_TABLE, see below.
676
677- Autoboot Command:
678		CONFIG_BOOTCOMMAND
679		Only needed when CONFIG_BOOTDELAY is enabled;
680		define a command string that is automatically executed
681		when no character is read on the console interface
682		within "Boot Delay" after reset.
683
684		CONFIG_RAMBOOT and CONFIG_NFSBOOT
685		The value of these goes into the environment as
686		"ramboot" and "nfsboot" respectively, and can be used
687		as a convenience, when switching between booting from
688		RAM and NFS.
689
690- Serial Download Echo Mode:
691		CONFIG_LOADS_ECHO
692		If defined to 1, all characters received during a
693		serial download (using the "loads" command) are
694		echoed back. This might be needed by some terminal
695		emulations (like "cu"), but may as well just take
696		time on others. This setting #define's the initial
697		value of the "loads_echo" environment variable.
698
699- Kgdb Serial Baudrate: (if CONFIG_CMD_KGDB is defined)
700		CONFIG_KGDB_BAUDRATE
701		Select one of the baudrates listed in
702		CONFIG_SYS_BAUDRATE_TABLE, see below.
703
704- Removal of commands
705		If no commands are needed to boot, you can disable
706		CONFIG_CMDLINE to remove them. In this case, the command line
707		will not be available, and when U-Boot wants to execute the
708		boot command (on start-up) it will call board_run_command()
709		instead. This can reduce image size significantly for very
710		simple boot procedures.
711
712- Regular expression support:
713		CONFIG_REGEX
714		If this variable is defined, U-Boot is linked against
715		the SLRE (Super Light Regular Expression) library,
716		which adds regex support to some commands, as for
717		example "env grep" and "setexpr".
718
719- Device tree:
720		CONFIG_OF_CONTROL
721		If this variable is defined, U-Boot will use a device tree
722		to configure its devices, instead of relying on statically
723		compiled #defines in the board file. This option is
724		experimental and only available on a few boards. The device
725		tree is available in the global data as gd->fdt_blob.
726
727		U-Boot needs to get its device tree from somewhere. This can
728		be done using one of the three options below:
729
730		CONFIG_OF_EMBED
731		If this variable is defined, U-Boot will embed a device tree
732		binary in its image. This device tree file should be in the
733		board directory and called <soc>-<board>.dts. The binary file
734		is then picked up in board_init_f() and made available through
735		the global data structure as gd->fdt_blob.
736
737		CONFIG_OF_SEPARATE
738		If this variable is defined, U-Boot will build a device tree
739		binary. It will be called u-boot.dtb. Architecture-specific
740		code will locate it at run-time. Generally this works by:
741
742			cat u-boot.bin u-boot.dtb >image.bin
743
744		and in fact, U-Boot does this for you, creating a file called
745		u-boot-dtb.bin which is useful in the common case. You can
746		still use the individual files if you need something more
747		exotic.
748
749		CONFIG_OF_BOARD
750		If this variable is defined, U-Boot will use the device tree
751		provided by the board at runtime instead of embedding one with
752		the image. Only boards defining board_fdt_blob_setup() support
753		this option (see include/fdtdec.h file).
754
755- Watchdog:
756		CONFIG_WATCHDOG
757		If this variable is defined, it enables watchdog
758		support for the SoC. There must be support in the SoC
759		specific code for a watchdog. For the 8xx
760		CPUs, the SIU Watchdog feature is enabled in the SYPCR
761		register.  When supported for a specific SoC is
762		available, then no further board specific code should
763		be needed to use it.
764
765		CONFIG_HW_WATCHDOG
766		When using a watchdog circuitry external to the used
767		SoC, then define this variable and provide board
768		specific code for the "hw_watchdog_reset" function.
769
770		CONFIG_AT91_HW_WDT_TIMEOUT
771		specify the timeout in seconds. default 2 seconds.
772
773- Real-Time Clock:
774
775		When CONFIG_CMD_DATE is selected, the type of the RTC
776		has to be selected, too. Define exactly one of the
777		following options:
778
779		CONFIG_RTC_PCF8563	- use Philips PCF8563 RTC
780		CONFIG_RTC_MC13XXX	- use MC13783 or MC13892 RTC
781		CONFIG_RTC_MC146818	- use MC146818 RTC
782		CONFIG_RTC_DS1307	- use Maxim, Inc. DS1307 RTC
783		CONFIG_RTC_DS1337	- use Maxim, Inc. DS1337 RTC
784		CONFIG_RTC_DS1338	- use Maxim, Inc. DS1338 RTC
785		CONFIG_RTC_DS1339	- use Maxim, Inc. DS1339 RTC
786		CONFIG_RTC_DS164x	- use Dallas DS164x RTC
787		CONFIG_RTC_ISL1208	- use Intersil ISL1208 RTC
788		CONFIG_RTC_MAX6900	- use Maxim, Inc. MAX6900 RTC
789		CONFIG_RTC_DS1337_NOOSC	- Turn off the OSC output for DS1337
790		CONFIG_SYS_RV3029_TCR	- enable trickle charger on
791					  RV3029 RTC.
792
793		Note that if the RTC uses I2C, then the I2C interface
794		must also be configured. See I2C Support, below.
795
796- GPIO Support:
797		CONFIG_PCA953X		- use NXP's PCA953X series I2C GPIO
798
799		The CONFIG_SYS_I2C_PCA953X_WIDTH option specifies a list of
800		chip-ngpio pairs that tell the PCA953X driver the number of
801		pins supported by a particular chip.
802
803		Note that if the GPIO device uses I2C, then the I2C interface
804		must also be configured. See I2C Support, below.
805
806- I/O tracing:
807		When CONFIG_IO_TRACE is selected, U-Boot intercepts all I/O
808		accesses and can checksum them or write a list of them out
809		to memory. See the 'iotrace' command for details. This is
810		useful for testing device drivers since it can confirm that
811		the driver behaves the same way before and after a code
812		change. Currently this is supported on sandbox and arm. To
813		add support for your architecture, add '#include <iotrace.h>'
814		to the bottom of arch/<arch>/include/asm/io.h and test.
815
816		Example output from the 'iotrace stats' command is below.
817		Note that if the trace buffer is exhausted, the checksum will
818		still continue to operate.
819
820			iotrace is enabled
821			Start:  10000000	(buffer start address)
822			Size:   00010000	(buffer size)
823			Offset: 00000120	(current buffer offset)
824			Output: 10000120	(start + offset)
825			Count:  00000018	(number of trace records)
826			CRC32:  9526fb66	(CRC32 of all trace records)
827
828- Timestamp Support:
829
830		When CONFIG_TIMESTAMP is selected, the timestamp
831		(date and time) of an image is printed by image
832		commands like bootm or iminfo. This option is
833		automatically enabled when you select CONFIG_CMD_DATE .
834
835- Partition Labels (disklabels) Supported:
836		Zero or more of the following:
837		CONFIG_MAC_PARTITION   Apple's MacOS partition table.
838		CONFIG_ISO_PARTITION   ISO partition table, used on CDROM etc.
839		CONFIG_EFI_PARTITION   GPT partition table, common when EFI is the
840				       bootloader.  Note 2TB partition limit; see
841				       disk/part_efi.c
842		CONFIG_SCSI) you must configure support for at
843		least one non-MTD partition type as well.
844
845- IDE Reset method:
846		CONFIG_IDE_RESET_ROUTINE - this is defined in several
847		board configurations files but used nowhere!
848
849		CONFIG_IDE_RESET - is this is defined, IDE Reset will
850		be performed by calling the function
851			ide_set_reset(int reset)
852		which has to be defined in a board specific file
853
854- ATAPI Support:
855		CONFIG_ATAPI
856
857		Set this to enable ATAPI support.
858
859- LBA48 Support
860		CONFIG_LBA48
861
862		Set this to enable support for disks larger than 137GB
863		Also look at CONFIG_SYS_64BIT_LBA.
864		Whithout these , LBA48 support uses 32bit variables and will 'only'
865		support disks up to 2.1TB.
866
867		CONFIG_SYS_64BIT_LBA:
868			When enabled, makes the IDE subsystem use 64bit sector addresses.
869			Default is 32bit.
870
871- SCSI Support:
872		CONFIG_SYS_SCSI_MAX_LUN [8], CONFIG_SYS_SCSI_MAX_SCSI_ID [7] and
873		CONFIG_SYS_SCSI_MAX_DEVICE [CONFIG_SYS_SCSI_MAX_SCSI_ID *
874		CONFIG_SYS_SCSI_MAX_LUN] can be adjusted to define the
875		maximum numbers of LUNs, SCSI ID's and target
876		devices.
877
878		The environment variable 'scsidevs' is set to the number of
879		SCSI devices found during the last scan.
880
881- NETWORK Support (PCI):
882		CONFIG_E1000
883		Support for Intel 8254x/8257x gigabit chips.
884
885		CONFIG_E1000_SPI
886		Utility code for direct access to the SPI bus on Intel 8257x.
887		This does not do anything useful unless you set at least one
888		of CONFIG_CMD_E1000 or CONFIG_E1000_SPI_GENERIC.
889
890		CONFIG_E1000_SPI_GENERIC
891		Allow generic access to the SPI bus on the Intel 8257x, for
892		example with the "sspi" command.
893
894		CONFIG_EEPRO100
895		Support for Intel 82557/82559/82559ER chips.
896		Optional CONFIG_EEPRO100_SROM_WRITE enables EEPROM
897		write routine for first time initialisation.
898
899		CONFIG_TULIP
900		Support for Digital 2114x chips.
901		Optional CONFIG_TULIP_SELECT_MEDIA for board specific
902		modem chip initialisation (KS8761/QS6611).
903
904		CONFIG_NATSEMI
905		Support for National dp83815 chips.
906
907		CONFIG_NS8382X
908		Support for National dp8382[01] gigabit chips.
909
910- NETWORK Support (other):
911
912		CONFIG_DRIVER_AT91EMAC
913		Support for AT91RM9200 EMAC.
914
915			CONFIG_RMII
916			Define this to use reduced MII inteface
917
918			CONFIG_DRIVER_AT91EMAC_QUIET
919			If this defined, the driver is quiet.
920			The driver doen't show link status messages.
921
922		CONFIG_CALXEDA_XGMAC
923		Support for the Calxeda XGMAC device
924
925		CONFIG_LAN91C96
926		Support for SMSC's LAN91C96 chips.
927
928			CONFIG_LAN91C96_USE_32_BIT
929			Define this to enable 32 bit addressing
930
931		CONFIG_SMC91111
932		Support for SMSC's LAN91C111 chip
933
934			CONFIG_SMC91111_BASE
935			Define this to hold the physical address
936			of the device (I/O space)
937
938			CONFIG_SMC_USE_32_BIT
939			Define this if data bus is 32 bits
940
941			CONFIG_SMC_USE_IOFUNCS
942			Define this to use i/o functions instead of macros
943			(some hardware wont work with macros)
944
945			CONFIG_SYS_DAVINCI_EMAC_PHY_COUNT
946			Define this if you have more then 3 PHYs.
947
948		CONFIG_FTGMAC100
949		Support for Faraday's FTGMAC100 Gigabit SoC Ethernet
950
951			CONFIG_FTGMAC100_EGIGA
952			Define this to use GE link update with gigabit PHY.
953			Define this if FTGMAC100 is connected to gigabit PHY.
954			If your system has 10/100 PHY only, it might not occur
955			wrong behavior. Because PHY usually return timeout or
956			useless data when polling gigabit status and gigabit
957			control registers. This behavior won't affect the
958			correctnessof 10/100 link speed update.
959
960		CONFIG_SH_ETHER
961		Support for Renesas on-chip Ethernet controller
962
963			CONFIG_SH_ETHER_USE_PORT
964			Define the number of ports to be used
965
966			CONFIG_SH_ETHER_PHY_ADDR
967			Define the ETH PHY's address
968
969			CONFIG_SH_ETHER_CACHE_WRITEBACK
970			If this option is set, the driver enables cache flush.
971
972- PWM Support:
973		CONFIG_PWM_IMX
974		Support for PWM module on the imx6.
975
976- TPM Support:
977		CONFIG_TPM
978		Support TPM devices.
979
980		CONFIG_TPM_TIS_INFINEON
981		Support for Infineon i2c bus TPM devices. Only one device
982		per system is supported at this time.
983
984			CONFIG_TPM_TIS_I2C_BURST_LIMITATION
985			Define the burst count bytes upper limit
986
987		CONFIG_TPM_ST33ZP24
988		Support for STMicroelectronics TPM devices. Requires DM_TPM support.
989
990			CONFIG_TPM_ST33ZP24_I2C
991			Support for STMicroelectronics ST33ZP24 I2C devices.
992			Requires TPM_ST33ZP24 and I2C.
993
994			CONFIG_TPM_ST33ZP24_SPI
995			Support for STMicroelectronics ST33ZP24 SPI devices.
996			Requires TPM_ST33ZP24 and SPI.
997
998		CONFIG_TPM_ATMEL_TWI
999		Support for Atmel TWI TPM device. Requires I2C support.
1000
1001		CONFIG_TPM_TIS_LPC
1002		Support for generic parallel port TPM devices. Only one device
1003		per system is supported at this time.
1004
1005			CONFIG_TPM_TIS_BASE_ADDRESS
1006			Base address where the generic TPM device is mapped
1007			to. Contemporary x86 systems usually map it at
1008			0xfed40000.
1009
1010		CONFIG_TPM
1011		Define this to enable the TPM support library which provides
1012		functional interfaces to some TPM commands.
1013		Requires support for a TPM device.
1014
1015		CONFIG_TPM_AUTH_SESSIONS
1016		Define this to enable authorized functions in the TPM library.
1017		Requires CONFIG_TPM and CONFIG_SHA1.
1018
1019- USB Support:
1020		At the moment only the UHCI host controller is
1021		supported (PIP405, MIP405); define
1022		CONFIG_USB_UHCI to enable it.
1023		define CONFIG_USB_KEYBOARD to enable the USB Keyboard
1024		and define CONFIG_USB_STORAGE to enable the USB
1025		storage devices.
1026		Note:
1027		Supported are USB Keyboards and USB Floppy drives
1028		(TEAC FD-05PUB).
1029
1030		CONFIG_USB_EHCI_TXFIFO_THRESH enables setting of the
1031		txfilltuning field in the EHCI controller on reset.
1032
1033		CONFIG_USB_DWC2_REG_ADDR the physical CPU address of the DWC2
1034		HW module registers.
1035
1036- USB Device:
1037		Define the below if you wish to use the USB console.
1038		Once firmware is rebuilt from a serial console issue the
1039		command "setenv stdin usbtty; setenv stdout usbtty" and
1040		attach your USB cable. The Unix command "dmesg" should print
1041		it has found a new device. The environment variable usbtty
1042		can be set to gserial or cdc_acm to enable your device to
1043		appear to a USB host as a Linux gserial device or a
1044		Common Device Class Abstract Control Model serial device.
1045		If you select usbtty = gserial you should be able to enumerate
1046		a Linux host by
1047		# modprobe usbserial vendor=0xVendorID product=0xProductID
1048		else if using cdc_acm, simply setting the environment
1049		variable usbtty to be cdc_acm should suffice. The following
1050		might be defined in YourBoardName.h
1051
1052			CONFIG_USB_DEVICE
1053			Define this to build a UDC device
1054
1055			CONFIG_USB_TTY
1056			Define this to have a tty type of device available to
1057			talk to the UDC device
1058
1059			CONFIG_USBD_HS
1060			Define this to enable the high speed support for usb
1061			device and usbtty. If this feature is enabled, a routine
1062			int is_usbd_high_speed(void)
1063			also needs to be defined by the driver to dynamically poll
1064			whether the enumeration has succeded at high speed or full
1065			speed.
1066
1067			CONFIG_SYS_CONSOLE_IS_IN_ENV
1068			Define this if you want stdin, stdout &/or stderr to
1069			be set to usbtty.
1070
1071		If you have a USB-IF assigned VendorID then you may wish to
1072		define your own vendor specific values either in BoardName.h
1073		or directly in usbd_vendor_info.h. If you don't define
1074		CONFIG_USBD_MANUFACTURER, CONFIG_USBD_PRODUCT_NAME,
1075		CONFIG_USBD_VENDORID and CONFIG_USBD_PRODUCTID, then U-Boot
1076		should pretend to be a Linux device to it's target host.
1077
1078			CONFIG_USBD_MANUFACTURER
1079			Define this string as the name of your company for
1080			- CONFIG_USBD_MANUFACTURER "my company"
1081
1082			CONFIG_USBD_PRODUCT_NAME
1083			Define this string as the name of your product
1084			- CONFIG_USBD_PRODUCT_NAME "acme usb device"
1085
1086			CONFIG_USBD_VENDORID
1087			Define this as your assigned Vendor ID from the USB
1088			Implementors Forum. This *must* be a genuine Vendor ID
1089			to avoid polluting the USB namespace.
1090			- CONFIG_USBD_VENDORID 0xFFFF
1091
1092			CONFIG_USBD_PRODUCTID
1093			Define this as the unique Product ID
1094			for your device
1095			- CONFIG_USBD_PRODUCTID 0xFFFF
1096
1097- ULPI Layer Support:
1098		The ULPI (UTMI Low Pin (count) Interface) PHYs are supported via
1099		the generic ULPI layer. The generic layer accesses the ULPI PHY
1100		via the platform viewport, so you need both the genric layer and
1101		the viewport enabled. Currently only Chipidea/ARC based
1102		viewport is supported.
1103		To enable the ULPI layer support, define CONFIG_USB_ULPI and
1104		CONFIG_USB_ULPI_VIEWPORT in your board configuration file.
1105		If your ULPI phy needs a different reference clock than the
1106		standard 24 MHz then you have to define CONFIG_ULPI_REF_CLK to
1107		the appropriate value in Hz.
1108
1109- MMC Support:
1110		The MMC controller on the Intel PXA is supported. To
1111		enable this define CONFIG_MMC. The MMC can be
1112		accessed from the boot prompt by mapping the device
1113		to physical memory similar to flash. Command line is
1114		enabled with CONFIG_CMD_MMC. The MMC driver also works with
1115		the FAT fs. This is enabled with CONFIG_CMD_FAT.
1116
1117		CONFIG_SH_MMCIF
1118		Support for Renesas on-chip MMCIF controller
1119
1120			CONFIG_SH_MMCIF_ADDR
1121			Define the base address of MMCIF registers
1122
1123			CONFIG_SH_MMCIF_CLK
1124			Define the clock frequency for MMCIF
1125
1126		CONFIG_SUPPORT_EMMC_BOOT
1127		Enable some additional features of the eMMC boot partitions.
1128
1129- USB Device Firmware Update (DFU) class support:
1130		CONFIG_DFU_OVER_USB
1131		This enables the USB portion of the DFU USB class
1132
1133		CONFIG_DFU_NAND
1134		This enables support for exposing NAND devices via DFU.
1135
1136		CONFIG_DFU_RAM
1137		This enables support for exposing RAM via DFU.
1138		Note: DFU spec refer to non-volatile memory usage, but
1139		allow usages beyond the scope of spec - here RAM usage,
1140		one that would help mostly the developer.
1141
1142		CONFIG_SYS_DFU_DATA_BUF_SIZE
1143		Dfu transfer uses a buffer before writing data to the
1144		raw storage device. Make the size (in bytes) of this buffer
1145		configurable. The size of this buffer is also configurable
1146		through the "dfu_bufsiz" environment variable.
1147
1148		CONFIG_SYS_DFU_MAX_FILE_SIZE
1149		When updating files rather than the raw storage device,
1150		we use a static buffer to copy the file into and then write
1151		the buffer once we've been given the whole file.  Define
1152		this to the maximum filesize (in bytes) for the buffer.
1153		Default is 4 MiB if undefined.
1154
1155		DFU_DEFAULT_POLL_TIMEOUT
1156		Poll timeout [ms], is the timeout a device can send to the
1157		host. The host must wait for this timeout before sending
1158		a subsequent DFU_GET_STATUS request to the device.
1159
1160		DFU_MANIFEST_POLL_TIMEOUT
1161		Poll timeout [ms], which the device sends to the host when
1162		entering dfuMANIFEST state. Host waits this timeout, before
1163		sending again an USB request to the device.
1164
1165- Journaling Flash filesystem support:
1166		CONFIG_JFFS2_NAND
1167		Define these for a default partition on a NAND device
1168
1169		CONFIG_SYS_JFFS2_FIRST_SECTOR,
1170		CONFIG_SYS_JFFS2_FIRST_BANK, CONFIG_SYS_JFFS2_NUM_BANKS
1171		Define these for a default partition on a NOR device
1172
1173- Keyboard Support:
1174		See Kconfig help for available keyboard drivers.
1175
1176		CONFIG_KEYBOARD
1177
1178		Define this to enable a custom keyboard support.
1179		This simply calls drv_keyboard_init() which must be
1180		defined in your board-specific files. This option is deprecated
1181		and is only used by novena. For new boards, use driver model
1182		instead.
1183
1184- Video support:
1185		CONFIG_FSL_DIU_FB
1186		Enable the Freescale DIU video driver.	Reference boards for
1187		SOCs that have a DIU should define this macro to enable DIU
1188		support, and should also define these other macros:
1189
1190			CONFIG_SYS_DIU_ADDR
1191			CONFIG_VIDEO
1192			CONFIG_CFB_CONSOLE
1193			CONFIG_VIDEO_SW_CURSOR
1194			CONFIG_VGA_AS_SINGLE_DEVICE
1195			CONFIG_VIDEO_LOGO
1196			CONFIG_VIDEO_BMP_LOGO
1197
1198		The DIU driver will look for the 'video-mode' environment
1199		variable, and if defined, enable the DIU as a console during
1200		boot.  See the documentation file doc/README.video for a
1201		description of this variable.
1202
1203- LCD Support:	CONFIG_LCD
1204
1205		Define this to enable LCD support (for output to LCD
1206		display); also select one of the supported displays
1207		by defining one of these:
1208
1209		CONFIG_ATMEL_LCD:
1210
1211			HITACHI TX09D70VM1CCA, 3.5", 240x320.
1212
1213		CONFIG_NEC_NL6448AC33:
1214
1215			NEC NL6448AC33-18. Active, color, single scan.
1216
1217		CONFIG_NEC_NL6448BC20
1218
1219			NEC NL6448BC20-08. 6.5", 640x480.
1220			Active, color, single scan.
1221
1222		CONFIG_NEC_NL6448BC33_54
1223
1224			NEC NL6448BC33-54. 10.4", 640x480.
1225			Active, color, single scan.
1226
1227		CONFIG_SHARP_16x9
1228
1229			Sharp 320x240. Active, color, single scan.
1230			It isn't 16x9, and I am not sure what it is.
1231
1232		CONFIG_SHARP_LQ64D341
1233
1234			Sharp LQ64D341 display, 640x480.
1235			Active, color, single scan.
1236
1237		CONFIG_HLD1045
1238
1239			HLD1045 display, 640x480.
1240			Active, color, single scan.
1241
1242		CONFIG_OPTREX_BW
1243
1244			Optrex	 CBL50840-2 NF-FW 99 22 M5
1245			or
1246			Hitachi	 LMG6912RPFC-00T
1247			or
1248			Hitachi	 SP14Q002
1249
1250			320x240. Black & white.
1251
1252		CONFIG_LCD_ALIGNMENT
1253
1254		Normally the LCD is page-aligned (typically 4KB). If this is
1255		defined then the LCD will be aligned to this value instead.
1256		For ARM it is sometimes useful to use MMU_SECTION_SIZE
1257		here, since it is cheaper to change data cache settings on
1258		a per-section basis.
1259
1260
1261		CONFIG_LCD_ROTATION
1262
1263		Sometimes, for example if the display is mounted in portrait
1264		mode or even if it's mounted landscape but rotated by 180degree,
1265		we need to rotate our content of the display relative to the
1266		framebuffer, so that user can read the messages which are
1267		printed out.
1268		Once CONFIG_LCD_ROTATION is defined, the lcd_console will be
1269		initialized with a given rotation from "vl_rot" out of
1270		"vidinfo_t" which is provided by the board specific code.
1271		The value for vl_rot is coded as following (matching to
1272		fbcon=rotate:<n> linux-kernel commandline):
1273		0 = no rotation respectively 0 degree
1274		1 = 90 degree rotation
1275		2 = 180 degree rotation
1276		3 = 270 degree rotation
1277
1278		If CONFIG_LCD_ROTATION is not defined, the console will be
1279		initialized with 0degree rotation.
1280
1281		CONFIG_LCD_BMP_RLE8
1282
1283		Support drawing of RLE8-compressed bitmaps on the LCD.
1284
1285		CONFIG_I2C_EDID
1286
1287		Enables an 'i2c edid' command which can read EDID
1288		information over I2C from an attached LCD display.
1289
1290- Splash Screen Support: CONFIG_SPLASH_SCREEN
1291
1292		If this option is set, the environment is checked for
1293		a variable "splashimage". If found, the usual display
1294		of logo, copyright and system information on the LCD
1295		is suppressed and the BMP image at the address
1296		specified in "splashimage" is loaded instead. The
1297		console is redirected to the "nulldev", too. This
1298		allows for a "silent" boot where a splash screen is
1299		loaded very quickly after power-on.
1300
1301		CONFIG_SPLASHIMAGE_GUARD
1302
1303		If this option is set, then U-Boot will prevent the environment
1304		variable "splashimage" from being set to a problematic address
1305		(see doc/README.displaying-bmps).
1306		This option is useful for targets where, due to alignment
1307		restrictions, an improperly aligned BMP image will cause a data
1308		abort. If you think you will not have problems with unaligned
1309		accesses (for example because your toolchain prevents them)
1310		there is no need to set this option.
1311
1312		CONFIG_SPLASH_SCREEN_ALIGN
1313
1314		If this option is set the splash image can be freely positioned
1315		on the screen. Environment variable "splashpos" specifies the
1316		position as "x,y". If a positive number is given it is used as
1317		number of pixel from left/top. If a negative number is given it
1318		is used as number of pixel from right/bottom. You can also
1319		specify 'm' for centering the image.
1320
1321		Example:
1322		setenv splashpos m,m
1323			=> image at center of screen
1324
1325		setenv splashpos 30,20
1326			=> image at x = 30 and y = 20
1327
1328		setenv splashpos -10,m
1329			=> vertically centered image
1330			   at x = dspWidth - bmpWidth - 9
1331
1332- Gzip compressed BMP image support: CONFIG_VIDEO_BMP_GZIP
1333
1334		If this option is set, additionally to standard BMP
1335		images, gzipped BMP images can be displayed via the
1336		splashscreen support or the bmp command.
1337
1338- Run length encoded BMP image (RLE8) support: CONFIG_VIDEO_BMP_RLE8
1339
1340		If this option is set, 8-bit RLE compressed BMP images
1341		can be displayed via the splashscreen support or the
1342		bmp command.
1343
1344- Compression support:
1345		CONFIG_GZIP
1346
1347		Enabled by default to support gzip compressed images.
1348
1349		CONFIG_BZIP2
1350
1351		If this option is set, support for bzip2 compressed
1352		images is included. If not, only uncompressed and gzip
1353		compressed images are supported.
1354
1355		NOTE: the bzip2 algorithm requires a lot of RAM, so
1356		the malloc area (as defined by CONFIG_SYS_MALLOC_LEN) should
1357		be at least 4MB.
1358
1359- MII/PHY support:
1360		CONFIG_PHY_CLOCK_FREQ (ppc4xx)
1361
1362		The clock frequency of the MII bus
1363
1364		CONFIG_PHY_RESET_DELAY
1365
1366		Some PHY like Intel LXT971A need extra delay after
1367		reset before any MII register access is possible.
1368		For such PHY, set this option to the usec delay
1369		required. (minimum 300usec for LXT971A)
1370
1371		CONFIG_PHY_CMD_DELAY (ppc4xx)
1372
1373		Some PHY like Intel LXT971A need extra delay after
1374		command issued before MII status register can be read
1375
1376- IP address:
1377		CONFIG_IPADDR
1378
1379		Define a default value for the IP address to use for
1380		the default Ethernet interface, in case this is not
1381		determined through e.g. bootp.
1382		(Environment variable "ipaddr")
1383
1384- Server IP address:
1385		CONFIG_SERVERIP
1386
1387		Defines a default value for the IP address of a TFTP
1388		server to contact when using the "tftboot" command.
1389		(Environment variable "serverip")
1390
1391		CONFIG_KEEP_SERVERADDR
1392
1393		Keeps the server's MAC address, in the env 'serveraddr'
1394		for passing to bootargs (like Linux's netconsole option)
1395
1396- Gateway IP address:
1397		CONFIG_GATEWAYIP
1398
1399		Defines a default value for the IP address of the
1400		default router where packets to other networks are
1401		sent to.
1402		(Environment variable "gatewayip")
1403
1404- Subnet mask:
1405		CONFIG_NETMASK
1406
1407		Defines a default value for the subnet mask (or
1408		routing prefix) which is used to determine if an IP
1409		address belongs to the local subnet or needs to be
1410		forwarded through a router.
1411		(Environment variable "netmask")
1412
1413- BOOTP Recovery Mode:
1414		CONFIG_BOOTP_RANDOM_DELAY
1415
1416		If you have many targets in a network that try to
1417		boot using BOOTP, you may want to avoid that all
1418		systems send out BOOTP requests at precisely the same
1419		moment (which would happen for instance at recovery
1420		from a power failure, when all systems will try to
1421		boot, thus flooding the BOOTP server. Defining
1422		CONFIG_BOOTP_RANDOM_DELAY causes a random delay to be
1423		inserted before sending out BOOTP requests. The
1424		following delays are inserted then:
1425
1426		1st BOOTP request:	delay 0 ... 1 sec
1427		2nd BOOTP request:	delay 0 ... 2 sec
1428		3rd BOOTP request:	delay 0 ... 4 sec
1429		4th and following
1430		BOOTP requests:		delay 0 ... 8 sec
1431
1432		CONFIG_BOOTP_ID_CACHE_SIZE
1433
1434		BOOTP packets are uniquely identified using a 32-bit ID. The
1435		server will copy the ID from client requests to responses and
1436		U-Boot will use this to determine if it is the destination of
1437		an incoming response. Some servers will check that addresses
1438		aren't in use before handing them out (usually using an ARP
1439		ping) and therefore take up to a few hundred milliseconds to
1440		respond. Network congestion may also influence the time it
1441		takes for a response to make it back to the client. If that
1442		time is too long, U-Boot will retransmit requests. In order
1443		to allow earlier responses to still be accepted after these
1444		retransmissions, U-Boot's BOOTP client keeps a small cache of
1445		IDs. The CONFIG_BOOTP_ID_CACHE_SIZE controls the size of this
1446		cache. The default is to keep IDs for up to four outstanding
1447		requests. Increasing this will allow U-Boot to accept offers
1448		from a BOOTP client in networks with unusually high latency.
1449
1450- DHCP Advanced Options:
1451		You can fine tune the DHCP functionality by defining
1452		CONFIG_BOOTP_* symbols:
1453
1454		CONFIG_BOOTP_NISDOMAIN
1455		CONFIG_BOOTP_BOOTFILESIZE
1456		CONFIG_BOOTP_SEND_HOSTNAME
1457		CONFIG_BOOTP_NTPSERVER
1458		CONFIG_BOOTP_TIMEOFFSET
1459		CONFIG_BOOTP_VENDOREX
1460		CONFIG_BOOTP_MAY_FAIL
1461
1462		CONFIG_BOOTP_SERVERIP - TFTP server will be the serverip
1463		environment variable, not the BOOTP server.
1464
1465		CONFIG_BOOTP_MAY_FAIL - If the DHCP server is not found
1466		after the configured retry count, the call will fail
1467		instead of starting over.  This can be used to fail over
1468		to Link-local IP address configuration if the DHCP server
1469		is not available.
1470
1471		CONFIG_BOOTP_SEND_HOSTNAME - Some DHCP servers are capable
1472		to do a dynamic update of a DNS server. To do this, they
1473		need the hostname of the DHCP requester.
1474		If CONFIG_BOOTP_SEND_HOSTNAME is defined, the content
1475		of the "hostname" environment variable is passed as
1476		option 12 to the DHCP server.
1477
1478		CONFIG_BOOTP_DHCP_REQUEST_DELAY
1479
1480		A 32bit value in microseconds for a delay between
1481		receiving a "DHCP Offer" and sending the "DHCP Request".
1482		This fixes a problem with certain DHCP servers that don't
1483		respond 100% of the time to a "DHCP request". E.g. On an
1484		AT91RM9200 processor running at 180MHz, this delay needed
1485		to be *at least* 15,000 usec before a Windows Server 2003
1486		DHCP server would reply 100% of the time. I recommend at
1487		least 50,000 usec to be safe. The alternative is to hope
1488		that one of the retries will be successful but note that
1489		the DHCP timeout and retry process takes a longer than
1490		this delay.
1491
1492 - Link-local IP address negotiation:
1493		Negotiate with other link-local clients on the local network
1494		for an address that doesn't require explicit configuration.
1495		This is especially useful if a DHCP server cannot be guaranteed
1496		to exist in all environments that the device must operate.
1497
1498		See doc/README.link-local for more information.
1499
1500 - MAC address from environment variables
1501
1502		FDT_SEQ_MACADDR_FROM_ENV
1503
1504		Fix-up device tree with MAC addresses fetched sequentially from
1505		environment variables. This config work on assumption that
1506		non-usable ethernet node of device-tree are either not present
1507		or their status has been marked as "disabled".
1508
1509 - CDP Options:
1510		CONFIG_CDP_DEVICE_ID
1511
1512		The device id used in CDP trigger frames.
1513
1514		CONFIG_CDP_DEVICE_ID_PREFIX
1515
1516		A two character string which is prefixed to the MAC address
1517		of the device.
1518
1519		CONFIG_CDP_PORT_ID
1520
1521		A printf format string which contains the ascii name of
1522		the port. Normally is set to "eth%d" which sets
1523		eth0 for the first Ethernet, eth1 for the second etc.
1524
1525		CONFIG_CDP_CAPABILITIES
1526
1527		A 32bit integer which indicates the device capabilities;
1528		0x00000010 for a normal host which does not forwards.
1529
1530		CONFIG_CDP_VERSION
1531
1532		An ascii string containing the version of the software.
1533
1534		CONFIG_CDP_PLATFORM
1535
1536		An ascii string containing the name of the platform.
1537
1538		CONFIG_CDP_TRIGGER
1539
1540		A 32bit integer sent on the trigger.
1541
1542		CONFIG_CDP_POWER_CONSUMPTION
1543
1544		A 16bit integer containing the power consumption of the
1545		device in .1 of milliwatts.
1546
1547		CONFIG_CDP_APPLIANCE_VLAN_TYPE
1548
1549		A byte containing the id of the VLAN.
1550
1551- Status LED:	CONFIG_LED_STATUS
1552
1553		Several configurations allow to display the current
1554		status using a LED. For instance, the LED will blink
1555		fast while running U-Boot code, stop blinking as
1556		soon as a reply to a BOOTP request was received, and
1557		start blinking slow once the Linux kernel is running
1558		(supported by a status LED driver in the Linux
1559		kernel). Defining CONFIG_LED_STATUS enables this
1560		feature in U-Boot.
1561
1562		Additional options:
1563
1564		CONFIG_LED_STATUS_GPIO
1565		The status LED can be connected to a GPIO pin.
1566		In such cases, the gpio_led driver can be used as a
1567		status LED backend implementation. Define CONFIG_LED_STATUS_GPIO
1568		to include the gpio_led driver in the U-Boot binary.
1569
1570		CONFIG_GPIO_LED_INVERTED_TABLE
1571		Some GPIO connected LEDs may have inverted polarity in which
1572		case the GPIO high value corresponds to LED off state and
1573		GPIO low value corresponds to LED on state.
1574		In such cases CONFIG_GPIO_LED_INVERTED_TABLE may be defined
1575		with a list of GPIO LEDs that have inverted polarity.
1576
1577- I2C Support:	CONFIG_SYS_I2C
1578
1579		This enable the NEW i2c subsystem, and will allow you to use
1580		i2c commands at the u-boot command line (as long as you set
1581		CONFIG_CMD_I2C in CONFIG_COMMANDS) and communicate with i2c
1582		based realtime clock chips or other i2c devices. See
1583		common/cmd_i2c.c for a description of the command line
1584		interface.
1585
1586		ported i2c driver to the new framework:
1587		- drivers/i2c/soft_i2c.c:
1588		  - activate first bus with CONFIG_SYS_I2C_SOFT define
1589		    CONFIG_SYS_I2C_SOFT_SPEED and CONFIG_SYS_I2C_SOFT_SLAVE
1590		    for defining speed and slave address
1591		  - activate second bus with I2C_SOFT_DECLARATIONS2 define
1592		    CONFIG_SYS_I2C_SOFT_SPEED_2 and CONFIG_SYS_I2C_SOFT_SLAVE_2
1593		    for defining speed and slave address
1594		  - activate third bus with I2C_SOFT_DECLARATIONS3 define
1595		    CONFIG_SYS_I2C_SOFT_SPEED_3 and CONFIG_SYS_I2C_SOFT_SLAVE_3
1596		    for defining speed and slave address
1597		  - activate fourth bus with I2C_SOFT_DECLARATIONS4 define
1598		    CONFIG_SYS_I2C_SOFT_SPEED_4 and CONFIG_SYS_I2C_SOFT_SLAVE_4
1599		    for defining speed and slave address
1600
1601		- drivers/i2c/fsl_i2c.c:
1602		  - activate i2c driver with CONFIG_SYS_I2C_FSL
1603		    define CONFIG_SYS_FSL_I2C_OFFSET for setting the register
1604		    offset CONFIG_SYS_FSL_I2C_SPEED for the i2c speed and
1605		    CONFIG_SYS_FSL_I2C_SLAVE for the slave addr of the first
1606		    bus.
1607		  - If your board supports a second fsl i2c bus, define
1608		    CONFIG_SYS_FSL_I2C2_OFFSET for the register offset
1609		    CONFIG_SYS_FSL_I2C2_SPEED for the speed and
1610		    CONFIG_SYS_FSL_I2C2_SLAVE for the slave address of the
1611		    second bus.
1612
1613		- drivers/i2c/tegra_i2c.c:
1614		  - activate this driver with CONFIG_SYS_I2C_TEGRA
1615		  - This driver adds 4 i2c buses with a fix speed from
1616		    100000 and the slave addr 0!
1617
1618		- drivers/i2c/ppc4xx_i2c.c
1619		  - activate this driver with CONFIG_SYS_I2C_PPC4XX
1620		  - CONFIG_SYS_I2C_PPC4XX_CH0 activate hardware channel 0
1621		  - CONFIG_SYS_I2C_PPC4XX_CH1 activate hardware channel 1
1622
1623		- drivers/i2c/i2c_mxc.c
1624		  - activate this driver with CONFIG_SYS_I2C_MXC
1625		  - enable bus 1 with CONFIG_SYS_I2C_MXC_I2C1
1626		  - enable bus 2 with CONFIG_SYS_I2C_MXC_I2C2
1627		  - enable bus 3 with CONFIG_SYS_I2C_MXC_I2C3
1628		  - enable bus 4 with CONFIG_SYS_I2C_MXC_I2C4
1629		  - define speed for bus 1 with CONFIG_SYS_MXC_I2C1_SPEED
1630		  - define slave for bus 1 with CONFIG_SYS_MXC_I2C1_SLAVE
1631		  - define speed for bus 2 with CONFIG_SYS_MXC_I2C2_SPEED
1632		  - define slave for bus 2 with CONFIG_SYS_MXC_I2C2_SLAVE
1633		  - define speed for bus 3 with CONFIG_SYS_MXC_I2C3_SPEED
1634		  - define slave for bus 3 with CONFIG_SYS_MXC_I2C3_SLAVE
1635		  - define speed for bus 4 with CONFIG_SYS_MXC_I2C4_SPEED
1636		  - define slave for bus 4 with CONFIG_SYS_MXC_I2C4_SLAVE
1637		If those defines are not set, default value is 100000
1638		for speed, and 0 for slave.
1639
1640		- drivers/i2c/rcar_i2c.c:
1641		  - activate this driver with CONFIG_SYS_I2C_RCAR
1642		  - This driver adds 4 i2c buses
1643
1644		  - CONFIG_SYS_RCAR_I2C0_BASE for setting the register channel 0
1645		  - CONFIG_SYS_RCAR_I2C0_SPEED for for the speed channel 0
1646		  - CONFIG_SYS_RCAR_I2C1_BASE for setting the register channel 1
1647		  - CONFIG_SYS_RCAR_I2C1_SPEED for for the speed channel 1
1648		  - CONFIG_SYS_RCAR_I2C2_BASE for setting the register channel 2
1649		  - CONFIG_SYS_RCAR_I2C2_SPEED for for the speed channel 2
1650		  - CONFIG_SYS_RCAR_I2C3_BASE for setting the register channel 3
1651		  - CONFIG_SYS_RCAR_I2C3_SPEED for for the speed channel 3
1652		  - CONFIF_SYS_RCAR_I2C_NUM_CONTROLLERS for number of i2c buses
1653
1654		- drivers/i2c/sh_i2c.c:
1655		  - activate this driver with CONFIG_SYS_I2C_SH
1656		  - This driver adds from 2 to 5 i2c buses
1657
1658		  - CONFIG_SYS_I2C_SH_BASE0 for setting the register channel 0
1659		  - CONFIG_SYS_I2C_SH_SPEED0 for for the speed channel 0
1660		  - CONFIG_SYS_I2C_SH_BASE1 for setting the register channel 1
1661		  - CONFIG_SYS_I2C_SH_SPEED1 for for the speed channel 1
1662		  - CONFIG_SYS_I2C_SH_BASE2 for setting the register channel 2
1663		  - CONFIG_SYS_I2C_SH_SPEED2 for for the speed channel 2
1664		  - CONFIG_SYS_I2C_SH_BASE3 for setting the register channel 3
1665		  - CONFIG_SYS_I2C_SH_SPEED3 for for the speed channel 3
1666		  - CONFIG_SYS_I2C_SH_BASE4 for setting the register channel 4
1667		  - CONFIG_SYS_I2C_SH_SPEED4 for for the speed channel 4
1668		  - CONFIG_SYS_I2C_SH_NUM_CONTROLLERS for number of i2c buses
1669
1670		- drivers/i2c/omap24xx_i2c.c
1671		  - activate this driver with CONFIG_SYS_I2C_OMAP24XX
1672		  - CONFIG_SYS_OMAP24_I2C_SPEED speed channel 0
1673		  - CONFIG_SYS_OMAP24_I2C_SLAVE slave addr channel 0
1674		  - CONFIG_SYS_OMAP24_I2C_SPEED1 speed channel 1
1675		  - CONFIG_SYS_OMAP24_I2C_SLAVE1 slave addr channel 1
1676		  - CONFIG_SYS_OMAP24_I2C_SPEED2 speed channel 2
1677		  - CONFIG_SYS_OMAP24_I2C_SLAVE2 slave addr channel 2
1678		  - CONFIG_SYS_OMAP24_I2C_SPEED3 speed channel 3
1679		  - CONFIG_SYS_OMAP24_I2C_SLAVE3 slave addr channel 3
1680		  - CONFIG_SYS_OMAP24_I2C_SPEED4 speed channel 4
1681		  - CONFIG_SYS_OMAP24_I2C_SLAVE4 slave addr channel 4
1682
1683		- drivers/i2c/s3c24x0_i2c.c:
1684		  - activate this driver with CONFIG_SYS_I2C_S3C24X0
1685		  - This driver adds i2c buses (11 for Exynos5250, Exynos5420
1686		    9 i2c buses for Exynos4 and 1 for S3C24X0 SoCs from Samsung)
1687		    with a fix speed from 100000 and the slave addr 0!
1688
1689		- drivers/i2c/ihs_i2c.c
1690		  - activate this driver with CONFIG_SYS_I2C_IHS
1691		  - CONFIG_SYS_I2C_IHS_CH0 activate hardware channel 0
1692		  - CONFIG_SYS_I2C_IHS_SPEED_0 speed channel 0
1693		  - CONFIG_SYS_I2C_IHS_SLAVE_0 slave addr channel 0
1694		  - CONFIG_SYS_I2C_IHS_CH1 activate hardware channel 1
1695		  - CONFIG_SYS_I2C_IHS_SPEED_1 speed channel 1
1696		  - CONFIG_SYS_I2C_IHS_SLAVE_1 slave addr channel 1
1697		  - CONFIG_SYS_I2C_IHS_CH2 activate hardware channel 2
1698		  - CONFIG_SYS_I2C_IHS_SPEED_2 speed channel 2
1699		  - CONFIG_SYS_I2C_IHS_SLAVE_2 slave addr channel 2
1700		  - CONFIG_SYS_I2C_IHS_CH3 activate hardware channel 3
1701		  - CONFIG_SYS_I2C_IHS_SPEED_3 speed channel 3
1702		  - CONFIG_SYS_I2C_IHS_SLAVE_3 slave addr channel 3
1703		  - activate dual channel with CONFIG_SYS_I2C_IHS_DUAL
1704		  - CONFIG_SYS_I2C_IHS_SPEED_0_1 speed channel 0_1
1705		  - CONFIG_SYS_I2C_IHS_SLAVE_0_1 slave addr channel 0_1
1706		  - CONFIG_SYS_I2C_IHS_SPEED_1_1 speed channel 1_1
1707		  - CONFIG_SYS_I2C_IHS_SLAVE_1_1 slave addr channel 1_1
1708		  - CONFIG_SYS_I2C_IHS_SPEED_2_1 speed channel 2_1
1709		  - CONFIG_SYS_I2C_IHS_SLAVE_2_1 slave addr channel 2_1
1710		  - CONFIG_SYS_I2C_IHS_SPEED_3_1 speed channel 3_1
1711		  - CONFIG_SYS_I2C_IHS_SLAVE_3_1 slave addr channel 3_1
1712
1713		additional defines:
1714
1715		CONFIG_SYS_NUM_I2C_BUSES
1716		Hold the number of i2c buses you want to use.
1717
1718		CONFIG_SYS_I2C_DIRECT_BUS
1719		define this, if you don't use i2c muxes on your hardware.
1720		if CONFIG_SYS_I2C_MAX_HOPS is not defined or == 0 you can
1721		omit this define.
1722
1723		CONFIG_SYS_I2C_MAX_HOPS
1724		define how many muxes are maximal consecutively connected
1725		on one i2c bus. If you not use i2c muxes, omit this
1726		define.
1727
1728		CONFIG_SYS_I2C_BUSES
1729		hold a list of buses you want to use, only used if
1730		CONFIG_SYS_I2C_DIRECT_BUS is not defined, for example
1731		a board with CONFIG_SYS_I2C_MAX_HOPS = 1 and
1732		CONFIG_SYS_NUM_I2C_BUSES = 9:
1733
1734		 CONFIG_SYS_I2C_BUSES	{{0, {I2C_NULL_HOP}}, \
1735					{0, {{I2C_MUX_PCA9547, 0x70, 1}}}, \
1736					{0, {{I2C_MUX_PCA9547, 0x70, 2}}}, \
1737					{0, {{I2C_MUX_PCA9547, 0x70, 3}}}, \
1738					{0, {{I2C_MUX_PCA9547, 0x70, 4}}}, \
1739					{0, {{I2C_MUX_PCA9547, 0x70, 5}}}, \
1740					{1, {I2C_NULL_HOP}}, \
1741					{1, {{I2C_MUX_PCA9544, 0x72, 1}}}, \
1742					{1, {{I2C_MUX_PCA9544, 0x72, 2}}}, \
1743					}
1744
1745		which defines
1746			bus 0 on adapter 0 without a mux
1747			bus 1 on adapter 0 with a PCA9547 on address 0x70 port 1
1748			bus 2 on adapter 0 with a PCA9547 on address 0x70 port 2
1749			bus 3 on adapter 0 with a PCA9547 on address 0x70 port 3
1750			bus 4 on adapter 0 with a PCA9547 on address 0x70 port 4
1751			bus 5 on adapter 0 with a PCA9547 on address 0x70 port 5
1752			bus 6 on adapter 1 without a mux
1753			bus 7 on adapter 1 with a PCA9544 on address 0x72 port 1
1754			bus 8 on adapter 1 with a PCA9544 on address 0x72 port 2
1755
1756		If you do not have i2c muxes on your board, omit this define.
1757
1758- Legacy I2C Support:
1759		If you use the software i2c interface (CONFIG_SYS_I2C_SOFT)
1760		then the following macros need to be defined (examples are
1761		from include/configs/lwmon.h):
1762
1763		I2C_INIT
1764
1765		(Optional). Any commands necessary to enable the I2C
1766		controller or configure ports.
1767
1768		eg: #define I2C_INIT (immr->im_cpm.cp_pbdir |=	PB_SCL)
1769
1770		I2C_ACTIVE
1771
1772		The code necessary to make the I2C data line active
1773		(driven).  If the data line is open collector, this
1774		define can be null.
1775
1776		eg: #define I2C_ACTIVE (immr->im_cpm.cp_pbdir |=  PB_SDA)
1777
1778		I2C_TRISTATE
1779
1780		The code necessary to make the I2C data line tri-stated
1781		(inactive).  If the data line is open collector, this
1782		define can be null.
1783
1784		eg: #define I2C_TRISTATE (immr->im_cpm.cp_pbdir &= ~PB_SDA)
1785
1786		I2C_READ
1787
1788		Code that returns true if the I2C data line is high,
1789		false if it is low.
1790
1791		eg: #define I2C_READ ((immr->im_cpm.cp_pbdat & PB_SDA) != 0)
1792
1793		I2C_SDA(bit)
1794
1795		If <bit> is true, sets the I2C data line high. If it
1796		is false, it clears it (low).
1797
1798		eg: #define I2C_SDA(bit) \
1799			if(bit) immr->im_cpm.cp_pbdat |=  PB_SDA; \
1800			else	immr->im_cpm.cp_pbdat &= ~PB_SDA
1801
1802		I2C_SCL(bit)
1803
1804		If <bit> is true, sets the I2C clock line high. If it
1805		is false, it clears it (low).
1806
1807		eg: #define I2C_SCL(bit) \
1808			if(bit) immr->im_cpm.cp_pbdat |=  PB_SCL; \
1809			else	immr->im_cpm.cp_pbdat &= ~PB_SCL
1810
1811		I2C_DELAY
1812
1813		This delay is invoked four times per clock cycle so this
1814		controls the rate of data transfer.  The data rate thus
1815		is 1 / (I2C_DELAY * 4). Often defined to be something
1816		like:
1817
1818		#define I2C_DELAY  udelay(2)
1819
1820		CONFIG_SOFT_I2C_GPIO_SCL / CONFIG_SOFT_I2C_GPIO_SDA
1821
1822		If your arch supports the generic GPIO framework (asm/gpio.h),
1823		then you may alternatively define the two GPIOs that are to be
1824		used as SCL / SDA.  Any of the previous I2C_xxx macros will
1825		have GPIO-based defaults assigned to them as appropriate.
1826
1827		You should define these to the GPIO value as given directly to
1828		the generic GPIO functions.
1829
1830		CONFIG_SYS_I2C_INIT_BOARD
1831
1832		When a board is reset during an i2c bus transfer
1833		chips might think that the current transfer is still
1834		in progress. On some boards it is possible to access
1835		the i2c SCLK line directly, either by using the
1836		processor pin as a GPIO or by having a second pin
1837		connected to the bus. If this option is defined a
1838		custom i2c_init_board() routine in boards/xxx/board.c
1839		is run early in the boot sequence.
1840
1841		CONFIG_I2C_MULTI_BUS
1842
1843		This option allows the use of multiple I2C buses, each of which
1844		must have a controller.	 At any point in time, only one bus is
1845		active.	 To switch to a different bus, use the 'i2c dev' command.
1846		Note that bus numbering is zero-based.
1847
1848		CONFIG_SYS_I2C_NOPROBES
1849
1850		This option specifies a list of I2C devices that will be skipped
1851		when the 'i2c probe' command is issued.	 If CONFIG_I2C_MULTI_BUS
1852		is set, specify a list of bus-device pairs.  Otherwise, specify
1853		a 1D array of device addresses
1854
1855		e.g.
1856			#undef	CONFIG_I2C_MULTI_BUS
1857			#define CONFIG_SYS_I2C_NOPROBES {0x50,0x68}
1858
1859		will skip addresses 0x50 and 0x68 on a board with one I2C bus
1860
1861			#define CONFIG_I2C_MULTI_BUS
1862			#define CONFIG_SYS_I2C_NOPROBES	{{0,0x50},{0,0x68},{1,0x54}}
1863
1864		will skip addresses 0x50 and 0x68 on bus 0 and address 0x54 on bus 1
1865
1866		CONFIG_SYS_SPD_BUS_NUM
1867
1868		If defined, then this indicates the I2C bus number for DDR SPD.
1869		If not defined, then U-Boot assumes that SPD is on I2C bus 0.
1870
1871		CONFIG_SYS_RTC_BUS_NUM
1872
1873		If defined, then this indicates the I2C bus number for the RTC.
1874		If not defined, then U-Boot assumes that RTC is on I2C bus 0.
1875
1876		CONFIG_SOFT_I2C_READ_REPEATED_START
1877
1878		defining this will force the i2c_read() function in
1879		the soft_i2c driver to perform an I2C repeated start
1880		between writing the address pointer and reading the
1881		data.  If this define is omitted the default behaviour
1882		of doing a stop-start sequence will be used.  Most I2C
1883		devices can use either method, but some require one or
1884		the other.
1885
1886- SPI Support:	CONFIG_SPI
1887
1888		Enables SPI driver (so far only tested with
1889		SPI EEPROM, also an instance works with Crystal A/D and
1890		D/As on the SACSng board)
1891
1892		CONFIG_SOFT_SPI
1893
1894		Enables a software (bit-bang) SPI driver rather than
1895		using hardware support. This is a general purpose
1896		driver that only requires three general I/O port pins
1897		(two outputs, one input) to function. If this is
1898		defined, the board configuration must define several
1899		SPI configuration items (port pins to use, etc). For
1900		an example, see include/configs/sacsng.h.
1901
1902		CONFIG_SYS_SPI_MXC_WAIT
1903		Timeout for waiting until spi transfer completed.
1904		default: (CONFIG_SYS_HZ/100)     /* 10 ms */
1905
1906- FPGA Support: CONFIG_FPGA
1907
1908		Enables FPGA subsystem.
1909
1910		CONFIG_FPGA_<vendor>
1911
1912		Enables support for specific chip vendors.
1913		(ALTERA, XILINX)
1914
1915		CONFIG_FPGA_<family>
1916
1917		Enables support for FPGA family.
1918		(SPARTAN2, SPARTAN3, VIRTEX2, CYCLONE2, ACEX1K, ACEX)
1919
1920		CONFIG_FPGA_COUNT
1921
1922		Specify the number of FPGA devices to support.
1923
1924		CONFIG_SYS_FPGA_PROG_FEEDBACK
1925
1926		Enable printing of hash marks during FPGA configuration.
1927
1928		CONFIG_SYS_FPGA_CHECK_BUSY
1929
1930		Enable checks on FPGA configuration interface busy
1931		status by the configuration function. This option
1932		will require a board or device specific function to
1933		be written.
1934
1935		CONFIG_FPGA_DELAY
1936
1937		If defined, a function that provides delays in the FPGA
1938		configuration driver.
1939
1940		CONFIG_SYS_FPGA_CHECK_CTRLC
1941		Allow Control-C to interrupt FPGA configuration
1942
1943		CONFIG_SYS_FPGA_CHECK_ERROR
1944
1945		Check for configuration errors during FPGA bitfile
1946		loading. For example, abort during Virtex II
1947		configuration if the INIT_B line goes low (which
1948		indicated a CRC error).
1949
1950		CONFIG_SYS_FPGA_WAIT_INIT
1951
1952		Maximum time to wait for the INIT_B line to de-assert
1953		after PROB_B has been de-asserted during a Virtex II
1954		FPGA configuration sequence. The default time is 500
1955		ms.
1956
1957		CONFIG_SYS_FPGA_WAIT_BUSY
1958
1959		Maximum time to wait for BUSY to de-assert during
1960		Virtex II FPGA configuration. The default is 5 ms.
1961
1962		CONFIG_SYS_FPGA_WAIT_CONFIG
1963
1964		Time to wait after FPGA configuration. The default is
1965		200 ms.
1966
1967- Configuration Management:
1968
1969		CONFIG_IDENT_STRING
1970
1971		If defined, this string will be added to the U-Boot
1972		version information (U_BOOT_VERSION)
1973
1974- Vendor Parameter Protection:
1975
1976		U-Boot considers the values of the environment
1977		variables "serial#" (Board Serial Number) and
1978		"ethaddr" (Ethernet Address) to be parameters that
1979		are set once by the board vendor / manufacturer, and
1980		protects these variables from casual modification by
1981		the user. Once set, these variables are read-only,
1982		and write or delete attempts are rejected. You can
1983		change this behaviour:
1984
1985		If CONFIG_ENV_OVERWRITE is #defined in your config
1986		file, the write protection for vendor parameters is
1987		completely disabled. Anybody can change or delete
1988		these parameters.
1989
1990		Alternatively, if you define _both_ an ethaddr in the
1991		default env _and_ CONFIG_OVERWRITE_ETHADDR_ONCE, a default
1992		Ethernet address is installed in the environment,
1993		which can be changed exactly ONCE by the user. [The
1994		serial# is unaffected by this, i. e. it remains
1995		read-only.]
1996
1997		The same can be accomplished in a more flexible way
1998		for any variable by configuring the type of access
1999		to allow for those variables in the ".flags" variable
2000		or define CONFIG_ENV_FLAGS_LIST_STATIC.
2001
2002- Protected RAM:
2003		CONFIG_PRAM
2004
2005		Define this variable to enable the reservation of
2006		"protected RAM", i. e. RAM which is not overwritten
2007		by U-Boot. Define CONFIG_PRAM to hold the number of
2008		kB you want to reserve for pRAM. You can overwrite
2009		this default value by defining an environment
2010		variable "pram" to the number of kB you want to
2011		reserve. Note that the board info structure will
2012		still show the full amount of RAM. If pRAM is
2013		reserved, a new environment variable "mem" will
2014		automatically be defined to hold the amount of
2015		remaining RAM in a form that can be passed as boot
2016		argument to Linux, for instance like that:
2017
2018			setenv bootargs ... mem=\${mem}
2019			saveenv
2020
2021		This way you can tell Linux not to use this memory,
2022		either, which results in a memory region that will
2023		not be affected by reboots.
2024
2025		*WARNING* If your board configuration uses automatic
2026		detection of the RAM size, you must make sure that
2027		this memory test is non-destructive. So far, the
2028		following board configurations are known to be
2029		"pRAM-clean":
2030
2031			IVMS8, IVML24, SPD8xx,
2032			HERMES, IP860, RPXlite, LWMON,
2033			FLAGADM
2034
2035- Access to physical memory region (> 4GB)
2036		Some basic support is provided for operations on memory not
2037		normally accessible to U-Boot - e.g. some architectures
2038		support access to more than 4GB of memory on 32-bit
2039		machines using physical address extension or similar.
2040		Define CONFIG_PHYSMEM to access this basic support, which
2041		currently only supports clearing the memory.
2042
2043- Error Recovery:
2044		CONFIG_NET_RETRY_COUNT
2045
2046		This variable defines the number of retries for
2047		network operations like ARP, RARP, TFTP, or BOOTP
2048		before giving up the operation. If not defined, a
2049		default value of 5 is used.
2050
2051		CONFIG_ARP_TIMEOUT
2052
2053		Timeout waiting for an ARP reply in milliseconds.
2054
2055		CONFIG_NFS_TIMEOUT
2056
2057		Timeout in milliseconds used in NFS protocol.
2058		If you encounter "ERROR: Cannot umount" in nfs command,
2059		try longer timeout such as
2060		#define CONFIG_NFS_TIMEOUT 10000UL
2061
2062- Command Interpreter:
2063		CONFIG_SYS_PROMPT_HUSH_PS2
2064
2065		This defines the secondary prompt string, which is
2066		printed when the command interpreter needs more input
2067		to complete a command. Usually "> ".
2068
2069	Note:
2070
2071		In the current implementation, the local variables
2072		space and global environment variables space are
2073		separated. Local variables are those you define by
2074		simply typing `name=value'. To access a local
2075		variable later on, you have write `$name' or
2076		`${name}'; to execute the contents of a variable
2077		directly type `$name' at the command prompt.
2078
2079		Global environment variables are those you use
2080		setenv/printenv to work with. To run a command stored
2081		in such a variable, you need to use the run command,
2082		and you must not use the '$' sign to access them.
2083
2084		To store commands and special characters in a
2085		variable, please use double quotation marks
2086		surrounding the whole text of the variable, instead
2087		of the backslashes before semicolons and special
2088		symbols.
2089
2090- Command Line Editing and History:
2091		CONFIG_CMDLINE_PS_SUPPORT
2092
2093		Enable support for changing the command prompt string
2094		at run-time. Only static string is supported so far.
2095		The string is obtained from environment variables PS1
2096		and PS2.
2097
2098- Default Environment:
2099		CONFIG_EXTRA_ENV_SETTINGS
2100
2101		Define this to contain any number of null terminated
2102		strings (variable = value pairs) that will be part of
2103		the default environment compiled into the boot image.
2104
2105		For example, place something like this in your
2106		board's config file:
2107
2108		#define CONFIG_EXTRA_ENV_SETTINGS \
2109			"myvar1=value1\0" \
2110			"myvar2=value2\0"
2111
2112		Warning: This method is based on knowledge about the
2113		internal format how the environment is stored by the
2114		U-Boot code. This is NOT an official, exported
2115		interface! Although it is unlikely that this format
2116		will change soon, there is no guarantee either.
2117		You better know what you are doing here.
2118
2119		Note: overly (ab)use of the default environment is
2120		discouraged. Make sure to check other ways to preset
2121		the environment like the "source" command or the
2122		boot command first.
2123
2124		CONFIG_DELAY_ENVIRONMENT
2125
2126		Normally the environment is loaded when the board is
2127		initialised so that it is available to U-Boot. This inhibits
2128		that so that the environment is not available until
2129		explicitly loaded later by U-Boot code. With CONFIG_OF_CONTROL
2130		this is instead controlled by the value of
2131		/config/load-environment.
2132
2133- TFTP Fixed UDP Port:
2134		CONFIG_TFTP_PORT
2135
2136		If this is defined, the environment variable tftpsrcp
2137		is used to supply the TFTP UDP source port value.
2138		If tftpsrcp isn't defined, the normal pseudo-random port
2139		number generator is used.
2140
2141		Also, the environment variable tftpdstp is used to supply
2142		the TFTP UDP destination port value.  If tftpdstp isn't
2143		defined, the normal port 69 is used.
2144
2145		The purpose for tftpsrcp is to allow a TFTP server to
2146		blindly start the TFTP transfer using the pre-configured
2147		target IP address and UDP port. This has the effect of
2148		"punching through" the (Windows XP) firewall, allowing
2149		the remainder of the TFTP transfer to proceed normally.
2150		A better solution is to properly configure the firewall,
2151		but sometimes that is not allowed.
2152
2153- Show boot progress:
2154		CONFIG_SHOW_BOOT_PROGRESS
2155
2156		Defining this option allows to add some board-
2157		specific code (calling a user-provided function
2158		"show_boot_progress(int)") that enables you to show
2159		the system's boot progress on some display (for
2160		example, some LED's) on your board. At the moment,
2161		the following checkpoints are implemented:
2162
2163
2164Legacy uImage format:
2165
2166  Arg	Where			When
2167    1	common/cmd_bootm.c	before attempting to boot an image
2168   -1	common/cmd_bootm.c	Image header has bad	 magic number
2169    2	common/cmd_bootm.c	Image header has correct magic number
2170   -2	common/cmd_bootm.c	Image header has bad	 checksum
2171    3	common/cmd_bootm.c	Image header has correct checksum
2172   -3	common/cmd_bootm.c	Image data   has bad	 checksum
2173    4	common/cmd_bootm.c	Image data   has correct checksum
2174   -4	common/cmd_bootm.c	Image is for unsupported architecture
2175    5	common/cmd_bootm.c	Architecture check OK
2176   -5	common/cmd_bootm.c	Wrong Image Type (not kernel, multi)
2177    6	common/cmd_bootm.c	Image Type check OK
2178   -6	common/cmd_bootm.c	gunzip uncompression error
2179   -7	common/cmd_bootm.c	Unimplemented compression type
2180    7	common/cmd_bootm.c	Uncompression OK
2181    8	common/cmd_bootm.c	No uncompress/copy overwrite error
2182   -9	common/cmd_bootm.c	Unsupported OS (not Linux, BSD, VxWorks, QNX)
2183
2184    9	common/image.c		Start initial ramdisk verification
2185  -10	common/image.c		Ramdisk header has bad	   magic number
2186  -11	common/image.c		Ramdisk header has bad	   checksum
2187   10	common/image.c		Ramdisk header is OK
2188  -12	common/image.c		Ramdisk data   has bad	   checksum
2189   11	common/image.c		Ramdisk data   has correct checksum
2190   12	common/image.c		Ramdisk verification complete, start loading
2191  -13	common/image.c		Wrong Image Type (not PPC Linux ramdisk)
2192   13	common/image.c		Start multifile image verification
2193   14	common/image.c		No initial ramdisk, no multifile, continue.
2194
2195   15	arch/<arch>/lib/bootm.c All preparation done, transferring control to OS
2196
2197  -30	arch/powerpc/lib/board.c	Fatal error, hang the system
2198  -31	post/post.c		POST test failed, detected by post_output_backlog()
2199  -32	post/post.c		POST test failed, detected by post_run_single()
2200
2201   34	common/cmd_doc.c	before loading a Image from a DOC device
2202  -35	common/cmd_doc.c	Bad usage of "doc" command
2203   35	common/cmd_doc.c	correct usage of "doc" command
2204  -36	common/cmd_doc.c	No boot device
2205   36	common/cmd_doc.c	correct boot device
2206  -37	common/cmd_doc.c	Unknown Chip ID on boot device
2207   37	common/cmd_doc.c	correct chip ID found, device available
2208  -38	common/cmd_doc.c	Read Error on boot device
2209   38	common/cmd_doc.c	reading Image header from DOC device OK
2210  -39	common/cmd_doc.c	Image header has bad magic number
2211   39	common/cmd_doc.c	Image header has correct magic number
2212  -40	common/cmd_doc.c	Error reading Image from DOC device
2213   40	common/cmd_doc.c	Image header has correct magic number
2214   41	common/cmd_ide.c	before loading a Image from a IDE device
2215  -42	common/cmd_ide.c	Bad usage of "ide" command
2216   42	common/cmd_ide.c	correct usage of "ide" command
2217  -43	common/cmd_ide.c	No boot device
2218   43	common/cmd_ide.c	boot device found
2219  -44	common/cmd_ide.c	Device not available
2220   44	common/cmd_ide.c	Device available
2221  -45	common/cmd_ide.c	wrong partition selected
2222   45	common/cmd_ide.c	partition selected
2223  -46	common/cmd_ide.c	Unknown partition table
2224   46	common/cmd_ide.c	valid partition table found
2225  -47	common/cmd_ide.c	Invalid partition type
2226   47	common/cmd_ide.c	correct partition type
2227  -48	common/cmd_ide.c	Error reading Image Header on boot device
2228   48	common/cmd_ide.c	reading Image Header from IDE device OK
2229  -49	common/cmd_ide.c	Image header has bad magic number
2230   49	common/cmd_ide.c	Image header has correct magic number
2231  -50	common/cmd_ide.c	Image header has bad	 checksum
2232   50	common/cmd_ide.c	Image header has correct checksum
2233  -51	common/cmd_ide.c	Error reading Image from IDE device
2234   51	common/cmd_ide.c	reading Image from IDE device OK
2235   52	common/cmd_nand.c	before loading a Image from a NAND device
2236  -53	common/cmd_nand.c	Bad usage of "nand" command
2237   53	common/cmd_nand.c	correct usage of "nand" command
2238  -54	common/cmd_nand.c	No boot device
2239   54	common/cmd_nand.c	boot device found
2240  -55	common/cmd_nand.c	Unknown Chip ID on boot device
2241   55	common/cmd_nand.c	correct chip ID found, device available
2242  -56	common/cmd_nand.c	Error reading Image Header on boot device
2243   56	common/cmd_nand.c	reading Image Header from NAND device OK
2244  -57	common/cmd_nand.c	Image header has bad magic number
2245   57	common/cmd_nand.c	Image header has correct magic number
2246  -58	common/cmd_nand.c	Error reading Image from NAND device
2247   58	common/cmd_nand.c	reading Image from NAND device OK
2248
2249  -60	common/env_common.c	Environment has a bad CRC, using default
2250
2251   64	net/eth.c		starting with Ethernet configuration.
2252  -64	net/eth.c		no Ethernet found.
2253   65	net/eth.c		Ethernet found.
2254
2255  -80	common/cmd_net.c	usage wrong
2256   80	common/cmd_net.c	before calling net_loop()
2257  -81	common/cmd_net.c	some error in net_loop() occurred
2258   81	common/cmd_net.c	net_loop() back without error
2259  -82	common/cmd_net.c	size == 0 (File with size 0 loaded)
2260   82	common/cmd_net.c	trying automatic boot
2261   83	common/cmd_net.c	running "source" command
2262  -83	common/cmd_net.c	some error in automatic boot or "source" command
2263   84	common/cmd_net.c	end without errors
2264
2265FIT uImage format:
2266
2267  Arg	Where			When
2268  100	common/cmd_bootm.c	Kernel FIT Image has correct format
2269 -100	common/cmd_bootm.c	Kernel FIT Image has incorrect format
2270  101	common/cmd_bootm.c	No Kernel subimage unit name, using configuration
2271 -101	common/cmd_bootm.c	Can't get configuration for kernel subimage
2272  102	common/cmd_bootm.c	Kernel unit name specified
2273 -103	common/cmd_bootm.c	Can't get kernel subimage node offset
2274  103	common/cmd_bootm.c	Found configuration node
2275  104	common/cmd_bootm.c	Got kernel subimage node offset
2276 -104	common/cmd_bootm.c	Kernel subimage hash verification failed
2277  105	common/cmd_bootm.c	Kernel subimage hash verification OK
2278 -105	common/cmd_bootm.c	Kernel subimage is for unsupported architecture
2279  106	common/cmd_bootm.c	Architecture check OK
2280 -106	common/cmd_bootm.c	Kernel subimage has wrong type
2281  107	common/cmd_bootm.c	Kernel subimage type OK
2282 -107	common/cmd_bootm.c	Can't get kernel subimage data/size
2283  108	common/cmd_bootm.c	Got kernel subimage data/size
2284 -108	common/cmd_bootm.c	Wrong image type (not legacy, FIT)
2285 -109	common/cmd_bootm.c	Can't get kernel subimage type
2286 -110	common/cmd_bootm.c	Can't get kernel subimage comp
2287 -111	common/cmd_bootm.c	Can't get kernel subimage os
2288 -112	common/cmd_bootm.c	Can't get kernel subimage load address
2289 -113	common/cmd_bootm.c	Image uncompress/copy overwrite error
2290
2291  120	common/image.c		Start initial ramdisk verification
2292 -120	common/image.c		Ramdisk FIT image has incorrect format
2293  121	common/image.c		Ramdisk FIT image has correct format
2294  122	common/image.c		No ramdisk subimage unit name, using configuration
2295 -122	common/image.c		Can't get configuration for ramdisk subimage
2296  123	common/image.c		Ramdisk unit name specified
2297 -124	common/image.c		Can't get ramdisk subimage node offset
2298  125	common/image.c		Got ramdisk subimage node offset
2299 -125	common/image.c		Ramdisk subimage hash verification failed
2300  126	common/image.c		Ramdisk subimage hash verification OK
2301 -126	common/image.c		Ramdisk subimage for unsupported architecture
2302  127	common/image.c		Architecture check OK
2303 -127	common/image.c		Can't get ramdisk subimage data/size
2304  128	common/image.c		Got ramdisk subimage data/size
2305  129	common/image.c		Can't get ramdisk load address
2306 -129	common/image.c		Got ramdisk load address
2307
2308 -130	common/cmd_doc.c	Incorrect FIT image format
2309  131	common/cmd_doc.c	FIT image format OK
2310
2311 -140	common/cmd_ide.c	Incorrect FIT image format
2312  141	common/cmd_ide.c	FIT image format OK
2313
2314 -150	common/cmd_nand.c	Incorrect FIT image format
2315  151	common/cmd_nand.c	FIT image format OK
2316
2317- Standalone program support:
2318		CONFIG_STANDALONE_LOAD_ADDR
2319
2320		This option defines a board specific value for the
2321		address where standalone program gets loaded, thus
2322		overwriting the architecture dependent default
2323		settings.
2324
2325- Frame Buffer Address:
2326		CONFIG_FB_ADDR
2327
2328		Define CONFIG_FB_ADDR if you want to use specific
2329		address for frame buffer.  This is typically the case
2330		when using a graphics controller has separate video
2331		memory.  U-Boot will then place the frame buffer at
2332		the given address instead of dynamically reserving it
2333		in system RAM by calling lcd_setmem(), which grabs
2334		the memory for the frame buffer depending on the
2335		configured panel size.
2336
2337		Please see board_init_f function.
2338
2339- Automatic software updates via TFTP server
2340		CONFIG_UPDATE_TFTP
2341		CONFIG_UPDATE_TFTP_CNT_MAX
2342		CONFIG_UPDATE_TFTP_MSEC_MAX
2343
2344		These options enable and control the auto-update feature;
2345		for a more detailed description refer to doc/README.update.
2346
2347- MTD Support (mtdparts command, UBI support)
2348		CONFIG_MTD_UBI_WL_THRESHOLD
2349		This parameter defines the maximum difference between the highest
2350		erase counter value and the lowest erase counter value of eraseblocks
2351		of UBI devices. When this threshold is exceeded, UBI starts performing
2352		wear leveling by means of moving data from eraseblock with low erase
2353		counter to eraseblocks with high erase counter.
2354
2355		The default value should be OK for SLC NAND flashes, NOR flashes and
2356		other flashes which have eraseblock life-cycle 100000 or more.
2357		However, in case of MLC NAND flashes which typically have eraseblock
2358		life-cycle less than 10000, the threshold should be lessened (e.g.,
2359		to 128 or 256, although it does not have to be power of 2).
2360
2361		default: 4096
2362
2363		CONFIG_MTD_UBI_BEB_LIMIT
2364		This option specifies the maximum bad physical eraseblocks UBI
2365		expects on the MTD device (per 1024 eraseblocks). If the
2366		underlying flash does not admit of bad eraseblocks (e.g. NOR
2367		flash), this value is ignored.
2368
2369		NAND datasheets often specify the minimum and maximum NVM
2370		(Number of Valid Blocks) for the flashes' endurance lifetime.
2371		The maximum expected bad eraseblocks per 1024 eraseblocks
2372		then can be calculated as "1024 * (1 - MinNVB / MaxNVB)",
2373		which gives 20 for most NANDs (MaxNVB is basically the total
2374		count of eraseblocks on the chip).
2375
2376		To put it differently, if this value is 20, UBI will try to
2377		reserve about 1.9% of physical eraseblocks for bad blocks
2378		handling. And that will be 1.9% of eraseblocks on the entire
2379		NAND chip, not just the MTD partition UBI attaches. This means
2380		that if you have, say, a NAND flash chip admits maximum 40 bad
2381		eraseblocks, and it is split on two MTD partitions of the same
2382		size, UBI will reserve 40 eraseblocks when attaching a
2383		partition.
2384
2385		default: 20
2386
2387		CONFIG_MTD_UBI_FASTMAP
2388		Fastmap is a mechanism which allows attaching an UBI device
2389		in nearly constant time. Instead of scanning the whole MTD device it
2390		only has to locate a checkpoint (called fastmap) on the device.
2391		The on-flash fastmap contains all information needed to attach
2392		the device. Using fastmap makes only sense on large devices where
2393		attaching by scanning takes long. UBI will not automatically install
2394		a fastmap on old images, but you can set the UBI parameter
2395		CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT to 1 if you want so. Please note
2396		that fastmap-enabled images are still usable with UBI implementations
2397		without	fastmap support. On typical flash devices the whole fastmap
2398		fits into one PEB. UBI will reserve PEBs to hold two fastmaps.
2399
2400		CONFIG_MTD_UBI_FASTMAP_AUTOCONVERT
2401		Set this parameter to enable fastmap automatically on images
2402		without a fastmap.
2403		default: 0
2404
2405		CONFIG_MTD_UBI_FM_DEBUG
2406		Enable UBI fastmap debug
2407		default: 0
2408
2409- SPL framework
2410		CONFIG_SPL
2411		Enable building of SPL globally.
2412
2413		CONFIG_SPL_LDSCRIPT
2414		LDSCRIPT for linking the SPL binary.
2415
2416		CONFIG_SPL_MAX_FOOTPRINT
2417		Maximum size in memory allocated to the SPL, BSS included.
2418		When defined, the linker checks that the actual memory
2419		used by SPL from _start to __bss_end does not exceed it.
2420		CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE
2421		must not be both defined at the same time.
2422
2423		CONFIG_SPL_MAX_SIZE
2424		Maximum size of the SPL image (text, data, rodata, and
2425		linker lists sections), BSS excluded.
2426		When defined, the linker checks that the actual size does
2427		not exceed it.
2428
2429		CONFIG_SPL_TEXT_BASE
2430		TEXT_BASE for linking the SPL binary.
2431
2432		CONFIG_SPL_RELOC_TEXT_BASE
2433		Address to relocate to.  If unspecified, this is equal to
2434		CONFIG_SPL_TEXT_BASE (i.e. no relocation is done).
2435
2436		CONFIG_SPL_BSS_START_ADDR
2437		Link address for the BSS within the SPL binary.
2438
2439		CONFIG_SPL_BSS_MAX_SIZE
2440		Maximum size in memory allocated to the SPL BSS.
2441		When defined, the linker checks that the actual memory used
2442		by SPL from __bss_start to __bss_end does not exceed it.
2443		CONFIG_SPL_MAX_FOOTPRINT and CONFIG_SPL_BSS_MAX_SIZE
2444		must not be both defined at the same time.
2445
2446		CONFIG_SPL_STACK
2447		Adress of the start of the stack SPL will use
2448
2449		CONFIG_SPL_PANIC_ON_RAW_IMAGE
2450		When defined, SPL will panic() if the image it has
2451		loaded does not have a signature.
2452		Defining this is useful when code which loads images
2453		in SPL cannot guarantee that absolutely all read errors
2454		will be caught.
2455		An example is the LPC32XX MLC NAND driver, which will
2456		consider that a completely unreadable NAND block is bad,
2457		and thus should be skipped silently.
2458
2459		CONFIG_SPL_RELOC_STACK
2460		Adress of the start of the stack SPL will use after
2461		relocation.  If unspecified, this is equal to
2462		CONFIG_SPL_STACK.
2463
2464		CONFIG_SYS_SPL_MALLOC_START
2465		Starting address of the malloc pool used in SPL.
2466		When this option is set the full malloc is used in SPL and
2467		it is set up by spl_init() and before that, the simple malloc()
2468		can be used if CONFIG_SYS_MALLOC_F is defined.
2469
2470		CONFIG_SYS_SPL_MALLOC_SIZE
2471		The size of the malloc pool used in SPL.
2472
2473		CONFIG_SPL_OS_BOOT
2474		Enable booting directly to an OS from SPL.
2475		See also: doc/README.falcon
2476
2477		CONFIG_SPL_DISPLAY_PRINT
2478		For ARM, enable an optional function to print more information
2479		about the running system.
2480
2481		CONFIG_SPL_INIT_MINIMAL
2482		Arch init code should be built for a very small image
2483
2484		CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_PARTITION
2485		Partition on the MMC to load U-Boot from when the MMC is being
2486		used in raw mode
2487
2488		CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR
2489		Sector to load kernel uImage from when MMC is being
2490		used in raw mode (for Falcon mode)
2491
2492		CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR,
2493		CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTORS
2494		Sector and number of sectors to load kernel argument
2495		parameters from when MMC is being used in raw mode
2496		(for falcon mode)
2497
2498		CONFIG_SYS_MMCSD_FS_BOOT_PARTITION
2499		Partition on the MMC to load U-Boot from when the MMC is being
2500		used in fs mode
2501
2502		CONFIG_SPL_FS_LOAD_PAYLOAD_NAME
2503		Filename to read to load U-Boot when reading from filesystem
2504
2505		CONFIG_SPL_FS_LOAD_KERNEL_NAME
2506		Filename to read to load kernel uImage when reading
2507		from filesystem (for Falcon mode)
2508
2509		CONFIG_SPL_FS_LOAD_ARGS_NAME
2510		Filename to read to load kernel argument parameters
2511		when reading from filesystem (for Falcon mode)
2512
2513		CONFIG_SPL_MPC83XX_WAIT_FOR_NAND
2514		Set this for NAND SPL on PPC mpc83xx targets, so that
2515		start.S waits for the rest of the SPL to load before
2516		continuing (the hardware starts execution after just
2517		loading the first page rather than the full 4K).
2518
2519		CONFIG_SPL_SKIP_RELOCATE
2520		Avoid SPL relocation
2521
2522		CONFIG_SPL_NAND_BASE
2523		Include nand_base.c in the SPL.  Requires
2524		CONFIG_SPL_NAND_DRIVERS.
2525
2526		CONFIG_SPL_NAND_DRIVERS
2527		SPL uses normal NAND drivers, not minimal drivers.
2528
2529		CONFIG_SPL_NAND_IDENT
2530		SPL uses the chip ID list to identify the NAND flash.
2531		Requires CONFIG_SPL_NAND_BASE.
2532
2533		CONFIG_SPL_NAND_ECC
2534		Include standard software ECC in the SPL
2535
2536		CONFIG_SPL_NAND_SIMPLE
2537		Support for NAND boot using simple NAND drivers that
2538		expose the cmd_ctrl() interface.
2539
2540		CONFIG_SPL_UBI
2541		Support for a lightweight UBI (fastmap) scanner and
2542		loader
2543
2544		CONFIG_SPL_NAND_RAW_ONLY
2545		Support to boot only raw u-boot.bin images. Use this only
2546		if you need to save space.
2547
2548		CONFIG_SPL_COMMON_INIT_DDR
2549		Set for common ddr init with serial presence detect in
2550		SPL binary.
2551
2552		CONFIG_SYS_NAND_5_ADDR_CYCLE, CONFIG_SYS_NAND_PAGE_COUNT,
2553		CONFIG_SYS_NAND_PAGE_SIZE, CONFIG_SYS_NAND_OOBSIZE,
2554		CONFIG_SYS_NAND_BLOCK_SIZE, CONFIG_SYS_NAND_BAD_BLOCK_POS,
2555		CONFIG_SYS_NAND_ECCPOS, CONFIG_SYS_NAND_ECCSIZE,
2556		CONFIG_SYS_NAND_ECCBYTES
2557		Defines the size and behavior of the NAND that SPL uses
2558		to read U-Boot
2559
2560		CONFIG_SPL_NAND_BOOT
2561		Add support NAND boot
2562
2563		CONFIG_SYS_NAND_U_BOOT_OFFS
2564		Location in NAND to read U-Boot from
2565
2566		CONFIG_SYS_NAND_U_BOOT_DST
2567		Location in memory to load U-Boot to
2568
2569		CONFIG_SYS_NAND_U_BOOT_SIZE
2570		Size of image to load
2571
2572		CONFIG_SYS_NAND_U_BOOT_START
2573		Entry point in loaded image to jump to
2574
2575		CONFIG_SYS_NAND_HW_ECC_OOBFIRST
2576		Define this if you need to first read the OOB and then the
2577		data. This is used, for example, on davinci platforms.
2578
2579		CONFIG_SPL_RAM_DEVICE
2580		Support for running image already present in ram, in SPL binary
2581
2582		CONFIG_SPL_PAD_TO
2583		Image offset to which the SPL should be padded before appending
2584		the SPL payload. By default, this is defined as
2585		CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.
2586		CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL
2587		payload without any padding, or >= CONFIG_SPL_MAX_SIZE.
2588
2589		CONFIG_SPL_TARGET
2590		Final target image containing SPL and payload.  Some SPLs
2591		use an arch-specific makefile fragment instead, for
2592		example if more than one image needs to be produced.
2593
2594		CONFIG_SPL_FIT_PRINT
2595		Printing information about a FIT image adds quite a bit of
2596		code to SPL. So this is normally disabled in SPL. Use this
2597		option to re-enable it. This will affect the output of the
2598		bootm command when booting a FIT image.
2599
2600- TPL framework
2601		CONFIG_TPL
2602		Enable building of TPL globally.
2603
2604		CONFIG_TPL_PAD_TO
2605		Image offset to which the TPL should be padded before appending
2606		the TPL payload. By default, this is defined as
2607		CONFIG_SPL_MAX_SIZE, or 0 if CONFIG_SPL_MAX_SIZE is undefined.
2608		CONFIG_SPL_PAD_TO must be either 0, meaning to append the SPL
2609		payload without any padding, or >= CONFIG_SPL_MAX_SIZE.
2610
2611- Interrupt support (PPC):
2612
2613		There are common interrupt_init() and timer_interrupt()
2614		for all PPC archs. interrupt_init() calls interrupt_init_cpu()
2615		for CPU specific initialization. interrupt_init_cpu()
2616		should set decrementer_count to appropriate value. If
2617		CPU resets decrementer automatically after interrupt
2618		(ppc4xx) it should set decrementer_count to zero.
2619		timer_interrupt() calls timer_interrupt_cpu() for CPU
2620		specific handling. If board has watchdog / status_led
2621		/ other_activity_monitor it works automatically from
2622		general timer_interrupt().
2623
2624
2625Board initialization settings:
2626------------------------------
2627
2628During Initialization u-boot calls a number of board specific functions
2629to allow the preparation of board specific prerequisites, e.g. pin setup
2630before drivers are initialized. To enable these callbacks the
2631following configuration macros have to be defined. Currently this is
2632architecture specific, so please check arch/your_architecture/lib/board.c
2633typically in board_init_f() and board_init_r().
2634
2635- CONFIG_BOARD_EARLY_INIT_F: Call board_early_init_f()
2636- CONFIG_BOARD_EARLY_INIT_R: Call board_early_init_r()
2637- CONFIG_BOARD_LATE_INIT: Call board_late_init()
2638- CONFIG_BOARD_POSTCLK_INIT: Call board_postclk_init()
2639
2640Configuration Settings:
2641-----------------------
2642
2643- CONFIG_SYS_SUPPORT_64BIT_DATA: Defined automatically if compiled as 64-bit.
2644		Optionally it can be defined to support 64-bit memory commands.
2645
2646- CONFIG_SYS_LONGHELP: Defined when you want long help messages included;
2647		undefine this when you're short of memory.
2648
2649- CONFIG_SYS_HELP_CMD_WIDTH: Defined when you want to override the default
2650		width of the commands listed in the 'help' command output.
2651
2652- CONFIG_SYS_PROMPT:	This is what U-Boot prints on the console to
2653		prompt for user input.
2654
2655- CONFIG_SYS_CBSIZE:	Buffer size for input from the Console
2656
2657- CONFIG_SYS_PBSIZE:	Buffer size for Console output
2658
2659- CONFIG_SYS_MAXARGS:	max. Number of arguments accepted for monitor commands
2660
2661- CONFIG_SYS_BARGSIZE: Buffer size for Boot Arguments which are passed to
2662		the application (usually a Linux kernel) when it is
2663		booted
2664
2665- CONFIG_SYS_BAUDRATE_TABLE:
2666		List of legal baudrate settings for this board.
2667
2668- CONFIG_SYS_MEMTEST_START, CONFIG_SYS_MEMTEST_END:
2669		Begin and End addresses of the area used by the
2670		simple memory test.
2671
2672- CONFIG_SYS_MEMTEST_SCRATCH:
2673		Scratch address used by the alternate memory test
2674		You only need to set this if address zero isn't writeable
2675
2676- CONFIG_SYS_MEM_RESERVE_SECURE
2677		Only implemented for ARMv8 for now.
2678		If defined, the size of CONFIG_SYS_MEM_RESERVE_SECURE memory
2679		is substracted from total RAM and won't be reported to OS.
2680		This memory can be used as secure memory. A variable
2681		gd->arch.secure_ram is used to track the location. In systems
2682		the RAM base is not zero, or RAM is divided into banks,
2683		this variable needs to be recalcuated to get the address.
2684
2685- CONFIG_SYS_MEM_TOP_HIDE:
2686		If CONFIG_SYS_MEM_TOP_HIDE is defined in the board config header,
2687		this specified memory area will get subtracted from the top
2688		(end) of RAM and won't get "touched" at all by U-Boot. By
2689		fixing up gd->ram_size the Linux kernel should gets passed
2690		the now "corrected" memory size and won't touch it either.
2691		This should work for arch/ppc and arch/powerpc. Only Linux
2692		board ports in arch/powerpc with bootwrapper support that
2693		recalculate the memory size from the SDRAM controller setup
2694		will have to get fixed in Linux additionally.
2695
2696		This option can be used as a workaround for the 440EPx/GRx
2697		CHIP 11 errata where the last 256 bytes in SDRAM shouldn't
2698		be touched.
2699
2700		WARNING: Please make sure that this value is a multiple of
2701		the Linux page size (normally 4k). If this is not the case,
2702		then the end address of the Linux memory will be located at a
2703		non page size aligned address and this could cause major
2704		problems.
2705
2706- CONFIG_SYS_LOADS_BAUD_CHANGE:
2707		Enable temporary baudrate change while serial download
2708
2709- CONFIG_SYS_SDRAM_BASE:
2710		Physical start address of SDRAM. _Must_ be 0 here.
2711
2712- CONFIG_SYS_FLASH_BASE:
2713		Physical start address of Flash memory.
2714
2715- CONFIG_SYS_MONITOR_BASE:
2716		Physical start address of boot monitor code (set by
2717		make config files to be same as the text base address
2718		(CONFIG_SYS_TEXT_BASE) used when linking) - same as
2719		CONFIG_SYS_FLASH_BASE when booting from flash.
2720
2721- CONFIG_SYS_MONITOR_LEN:
2722		Size of memory reserved for monitor code, used to
2723		determine _at_compile_time_ (!) if the environment is
2724		embedded within the U-Boot image, or in a separate
2725		flash sector.
2726
2727- CONFIG_SYS_MALLOC_LEN:
2728		Size of DRAM reserved for malloc() use.
2729
2730- CONFIG_SYS_MALLOC_F_LEN
2731		Size of the malloc() pool for use before relocation. If
2732		this is defined, then a very simple malloc() implementation
2733		will become available before relocation. The address is just
2734		below the global data, and the stack is moved down to make
2735		space.
2736
2737		This feature allocates regions with increasing addresses
2738		within the region. calloc() is supported, but realloc()
2739		is not available. free() is supported but does nothing.
2740		The memory will be freed (or in fact just forgotten) when
2741		U-Boot relocates itself.
2742
2743- CONFIG_SYS_MALLOC_SIMPLE
2744		Provides a simple and small malloc() and calloc() for those
2745		boards which do not use the full malloc in SPL (which is
2746		enabled with CONFIG_SYS_SPL_MALLOC_START).
2747
2748- CONFIG_SYS_NONCACHED_MEMORY:
2749		Size of non-cached memory area. This area of memory will be
2750		typically located right below the malloc() area and mapped
2751		uncached in the MMU. This is useful for drivers that would
2752		otherwise require a lot of explicit cache maintenance. For
2753		some drivers it's also impossible to properly maintain the
2754		cache. For example if the regions that need to be flushed
2755		are not a multiple of the cache-line size, *and* padding
2756		cannot be allocated between the regions to align them (i.e.
2757		if the HW requires a contiguous array of regions, and the
2758		size of each region is not cache-aligned), then a flush of
2759		one region may result in overwriting data that hardware has
2760		written to another region in the same cache-line. This can
2761		happen for example in network drivers where descriptors for
2762		buffers are typically smaller than the CPU cache-line (e.g.
2763		16 bytes vs. 32 or 64 bytes).
2764
2765		Non-cached memory is only supported on 32-bit ARM at present.
2766
2767- CONFIG_SYS_BOOTM_LEN:
2768		Normally compressed uImages are limited to an
2769		uncompressed size of 8 MBytes. If this is not enough,
2770		you can define CONFIG_SYS_BOOTM_LEN in your board config file
2771		to adjust this setting to your needs.
2772
2773- CONFIG_SYS_BOOTMAPSZ:
2774		Maximum size of memory mapped by the startup code of
2775		the Linux kernel; all data that must be processed by
2776		the Linux kernel (bd_info, boot arguments, FDT blob if
2777		used) must be put below this limit, unless "bootm_low"
2778		environment variable is defined and non-zero. In such case
2779		all data for the Linux kernel must be between "bootm_low"
2780		and "bootm_low" + CONFIG_SYS_BOOTMAPSZ.	 The environment
2781		variable "bootm_mapsize" will override the value of
2782		CONFIG_SYS_BOOTMAPSZ.  If CONFIG_SYS_BOOTMAPSZ is undefined,
2783		then the value in "bootm_size" will be used instead.
2784
2785- CONFIG_SYS_BOOT_RAMDISK_HIGH:
2786		Enable initrd_high functionality.  If defined then the
2787		initrd_high feature is enabled and the bootm ramdisk subcommand
2788		is enabled.
2789
2790- CONFIG_SYS_BOOT_GET_CMDLINE:
2791		Enables allocating and saving kernel cmdline in space between
2792		"bootm_low" and "bootm_low" + BOOTMAPSZ.
2793
2794- CONFIG_SYS_BOOT_GET_KBD:
2795		Enables allocating and saving a kernel copy of the bd_info in
2796		space between "bootm_low" and "bootm_low" + BOOTMAPSZ.
2797
2798- CONFIG_SYS_MAX_FLASH_BANKS:
2799		Max number of Flash memory banks
2800
2801- CONFIG_SYS_MAX_FLASH_SECT:
2802		Max number of sectors on a Flash chip
2803
2804- CONFIG_SYS_FLASH_ERASE_TOUT:
2805		Timeout for Flash erase operations (in ms)
2806
2807- CONFIG_SYS_FLASH_WRITE_TOUT:
2808		Timeout for Flash write operations (in ms)
2809
2810- CONFIG_SYS_FLASH_LOCK_TOUT
2811		Timeout for Flash set sector lock bit operation (in ms)
2812
2813- CONFIG_SYS_FLASH_UNLOCK_TOUT
2814		Timeout for Flash clear lock bits operation (in ms)
2815
2816- CONFIG_SYS_FLASH_PROTECTION
2817		If defined, hardware flash sectors protection is used
2818		instead of U-Boot software protection.
2819
2820- CONFIG_SYS_DIRECT_FLASH_TFTP:
2821
2822		Enable TFTP transfers directly to flash memory;
2823		without this option such a download has to be
2824		performed in two steps: (1) download to RAM, and (2)
2825		copy from RAM to flash.
2826
2827		The two-step approach is usually more reliable, since
2828		you can check if the download worked before you erase
2829		the flash, but in some situations (when system RAM is
2830		too limited to allow for a temporary copy of the
2831		downloaded image) this option may be very useful.
2832
2833- CONFIG_SYS_FLASH_CFI:
2834		Define if the flash driver uses extra elements in the
2835		common flash structure for storing flash geometry.
2836
2837- CONFIG_FLASH_CFI_DRIVER
2838		This option also enables the building of the cfi_flash driver
2839		in the drivers directory
2840
2841- CONFIG_FLASH_CFI_MTD
2842		This option enables the building of the cfi_mtd driver
2843		in the drivers directory. The driver exports CFI flash
2844		to the MTD layer.
2845
2846- CONFIG_SYS_FLASH_USE_BUFFER_WRITE
2847		Use buffered writes to flash.
2848
2849- CONFIG_FLASH_SPANSION_S29WS_N
2850		s29ws-n MirrorBit flash has non-standard addresses for buffered
2851		write commands.
2852
2853- CONFIG_SYS_FLASH_QUIET_TEST
2854		If this option is defined, the common CFI flash doesn't
2855		print it's warning upon not recognized FLASH banks. This
2856		is useful, if some of the configured banks are only
2857		optionally available.
2858
2859- CONFIG_FLASH_SHOW_PROGRESS
2860		If defined (must be an integer), print out countdown
2861		digits and dots.  Recommended value: 45 (9..1) for 80
2862		column displays, 15 (3..1) for 40 column displays.
2863
2864- CONFIG_FLASH_VERIFY
2865		If defined, the content of the flash (destination) is compared
2866		against the source after the write operation. An error message
2867		will be printed when the contents are not identical.
2868		Please note that this option is useless in nearly all cases,
2869		since such flash programming errors usually are detected earlier
2870		while unprotecting/erasing/programming. Please only enable
2871		this option if you really know what you are doing.
2872
2873- CONFIG_SYS_RX_ETH_BUFFER:
2874		Defines the number of Ethernet receive buffers. On some
2875		Ethernet controllers it is recommended to set this value
2876		to 8 or even higher (EEPRO100 or 405 EMAC), since all
2877		buffers can be full shortly after enabling the interface
2878		on high Ethernet traffic.
2879		Defaults to 4 if not defined.
2880
2881- CONFIG_ENV_MAX_ENTRIES
2882
2883	Maximum number of entries in the hash table that is used
2884	internally to store the environment settings. The default
2885	setting is supposed to be generous and should work in most
2886	cases. This setting can be used to tune behaviour; see
2887	lib/hashtable.c for details.
2888
2889- CONFIG_ENV_FLAGS_LIST_DEFAULT
2890- CONFIG_ENV_FLAGS_LIST_STATIC
2891	Enable validation of the values given to environment variables when
2892	calling env set.  Variables can be restricted to only decimal,
2893	hexadecimal, or boolean.  If CONFIG_CMD_NET is also defined,
2894	the variables can also be restricted to IP address or MAC address.
2895
2896	The format of the list is:
2897		type_attribute = [s|d|x|b|i|m]
2898		access_attribute = [a|r|o|c]
2899		attributes = type_attribute[access_attribute]
2900		entry = variable_name[:attributes]
2901		list = entry[,list]
2902
2903	The type attributes are:
2904		s - String (default)
2905		d - Decimal
2906		x - Hexadecimal
2907		b - Boolean ([1yYtT|0nNfF])
2908		i - IP address
2909		m - MAC address
2910
2911	The access attributes are:
2912		a - Any (default)
2913		r - Read-only
2914		o - Write-once
2915		c - Change-default
2916
2917	- CONFIG_ENV_FLAGS_LIST_DEFAULT
2918		Define this to a list (string) to define the ".flags"
2919		environment variable in the default or embedded environment.
2920
2921	- CONFIG_ENV_FLAGS_LIST_STATIC
2922		Define this to a list (string) to define validation that
2923		should be done if an entry is not found in the ".flags"
2924		environment variable.  To override a setting in the static
2925		list, simply add an entry for the same variable name to the
2926		".flags" variable.
2927
2928	If CONFIG_REGEX is defined, the variable_name above is evaluated as a
2929	regular expression. This allows multiple variables to define the same
2930	flags without explicitly listing them for each variable.
2931
2932- CONFIG_ENV_ACCESS_IGNORE_FORCE
2933	If defined, don't allow the -f switch to env set override variable
2934	access flags.
2935
2936The following definitions that deal with the placement and management
2937of environment data (variable area); in general, we support the
2938following configurations:
2939
2940- CONFIG_BUILD_ENVCRC:
2941
2942	Builds up envcrc with the target environment so that external utils
2943	may easily extract it and embed it in final U-Boot images.
2944
2945BE CAREFUL! The first access to the environment happens quite early
2946in U-Boot initialization (when we try to get the setting of for the
2947console baudrate). You *MUST* have mapped your NVRAM area then, or
2948U-Boot will hang.
2949
2950Please note that even with NVRAM we still use a copy of the
2951environment in RAM: we could work on NVRAM directly, but we want to
2952keep settings there always unmodified except somebody uses "saveenv"
2953to save the current settings.
2954
2955BE CAREFUL! For some special cases, the local device can not use
2956"saveenv" command. For example, the local device will get the
2957environment stored in a remote NOR flash by SRIO or PCIE link,
2958but it can not erase, write this NOR flash by SRIO or PCIE interface.
2959
2960- CONFIG_NAND_ENV_DST
2961
2962	Defines address in RAM to which the nand_spl code should copy the
2963	environment. If redundant environment is used, it will be copied to
2964	CONFIG_NAND_ENV_DST + CONFIG_ENV_SIZE.
2965
2966Please note that the environment is read-only until the monitor
2967has been relocated to RAM and a RAM copy of the environment has been
2968created; also, when using EEPROM you will have to use env_get_f()
2969until then to read environment variables.
2970
2971The environment is protected by a CRC32 checksum. Before the monitor
2972is relocated into RAM, as a result of a bad CRC you will be working
2973with the compiled-in default environment - *silently*!!! [This is
2974necessary, because the first environment variable we need is the
2975"baudrate" setting for the console - if we have a bad CRC, we don't
2976have any device yet where we could complain.]
2977
2978Note: once the monitor has been relocated, then it will complain if
2979the default environment is used; a new CRC is computed as soon as you
2980use the "saveenv" command to store a valid environment.
2981
2982- CONFIG_SYS_FAULT_ECHO_LINK_DOWN:
2983		Echo the inverted Ethernet link state to the fault LED.
2984
2985		Note: If this option is active, then CONFIG_SYS_FAULT_MII_ADDR
2986		      also needs to be defined.
2987
2988- CONFIG_SYS_FAULT_MII_ADDR:
2989		MII address of the PHY to check for the Ethernet link state.
2990
2991- CONFIG_NS16550_MIN_FUNCTIONS:
2992		Define this if you desire to only have use of the NS16550_init
2993		and NS16550_putc functions for the serial driver located at
2994		drivers/serial/ns16550.c.  This option is useful for saving
2995		space for already greatly restricted images, including but not
2996		limited to NAND_SPL configurations.
2997
2998- CONFIG_DISPLAY_BOARDINFO
2999		Display information about the board that U-Boot is running on
3000		when U-Boot starts up. The board function checkboard() is called
3001		to do this.
3002
3003- CONFIG_DISPLAY_BOARDINFO_LATE
3004		Similar to the previous option, but display this information
3005		later, once stdio is running and output goes to the LCD, if
3006		present.
3007
3008- CONFIG_BOARD_SIZE_LIMIT:
3009		Maximum size of the U-Boot image. When defined, the
3010		build system checks that the actual size does not
3011		exceed it.
3012
3013Low Level (hardware related) configuration options:
3014---------------------------------------------------
3015
3016- CONFIG_SYS_CACHELINE_SIZE:
3017		Cache Line Size of the CPU.
3018
3019- CONFIG_SYS_CCSRBAR_DEFAULT:
3020		Default (power-on reset) physical address of CCSR on Freescale
3021		PowerPC SOCs.
3022
3023- CONFIG_SYS_CCSRBAR:
3024		Virtual address of CCSR.  On a 32-bit build, this is typically
3025		the same value as CONFIG_SYS_CCSRBAR_DEFAULT.
3026
3027- CONFIG_SYS_CCSRBAR_PHYS:
3028		Physical address of CCSR.  CCSR can be relocated to a new
3029		physical address, if desired.  In this case, this macro should
3030		be set to that address.	 Otherwise, it should be set to the
3031		same value as CONFIG_SYS_CCSRBAR_DEFAULT.  For example, CCSR
3032		is typically relocated on 36-bit builds.  It is recommended
3033		that this macro be defined via the _HIGH and _LOW macros:
3034
3035		#define CONFIG_SYS_CCSRBAR_PHYS ((CONFIG_SYS_CCSRBAR_PHYS_HIGH
3036			* 1ull) << 32 | CONFIG_SYS_CCSRBAR_PHYS_LOW)
3037
3038- CONFIG_SYS_CCSRBAR_PHYS_HIGH:
3039		Bits 33-36 of CONFIG_SYS_CCSRBAR_PHYS.	This value is typically
3040		either 0 (32-bit build) or 0xF (36-bit build).	This macro is
3041		used in assembly code, so it must not contain typecasts or
3042		integer size suffixes (e.g. "ULL").
3043
3044- CONFIG_SYS_CCSRBAR_PHYS_LOW:
3045		Lower 32-bits of CONFIG_SYS_CCSRBAR_PHYS.  This macro is
3046		used in assembly code, so it must not contain typecasts or
3047		integer size suffixes (e.g. "ULL").
3048
3049- CONFIG_SYS_CCSR_DO_NOT_RELOCATE:
3050		If this macro is defined, then CONFIG_SYS_CCSRBAR_PHYS will be
3051		forced to a value that ensures that CCSR is not relocated.
3052
3053- Floppy Disk Support:
3054		CONFIG_SYS_FDC_DRIVE_NUMBER
3055
3056		the default drive number (default value 0)
3057
3058		CONFIG_SYS_ISA_IO_STRIDE
3059
3060		defines the spacing between FDC chipset registers
3061		(default value 1)
3062
3063		CONFIG_SYS_ISA_IO_OFFSET
3064
3065		defines the offset of register from address. It
3066		depends on which part of the data bus is connected to
3067		the FDC chipset. (default value 0)
3068
3069		If CONFIG_SYS_ISA_IO_STRIDE CONFIG_SYS_ISA_IO_OFFSET and
3070		CONFIG_SYS_FDC_DRIVE_NUMBER are undefined, they take their
3071		default value.
3072
3073		if CONFIG_SYS_FDC_HW_INIT is defined, then the function
3074		fdc_hw_init() is called at the beginning of the FDC
3075		setup. fdc_hw_init() must be provided by the board
3076		source code. It is used to make hardware-dependent
3077		initializations.
3078
3079- CONFIG_IDE_AHB:
3080		Most IDE controllers were designed to be connected with PCI
3081		interface. Only few of them were designed for AHB interface.
3082		When software is doing ATA command and data transfer to
3083		IDE devices through IDE-AHB controller, some additional
3084		registers accessing to these kind of IDE-AHB controller
3085		is required.
3086
3087- CONFIG_SYS_IMMR:	Physical address of the Internal Memory.
3088		DO NOT CHANGE unless you know exactly what you're
3089		doing! (11-4) [MPC8xx systems only]
3090
3091- CONFIG_SYS_INIT_RAM_ADDR:
3092
3093		Start address of memory area that can be used for
3094		initial data and stack; please note that this must be
3095		writable memory that is working WITHOUT special
3096		initialization, i. e. you CANNOT use normal RAM which
3097		will become available only after programming the
3098		memory controller and running certain initialization
3099		sequences.
3100
3101		U-Boot uses the following memory types:
3102		- MPC8xx: IMMR (internal memory of the CPU)
3103
3104- CONFIG_SYS_GBL_DATA_OFFSET:
3105
3106		Offset of the initial data structure in the memory
3107		area defined by CONFIG_SYS_INIT_RAM_ADDR. Usually
3108		CONFIG_SYS_GBL_DATA_OFFSET is chosen such that the initial
3109		data is located at the end of the available space
3110		(sometimes written as (CONFIG_SYS_INIT_RAM_SIZE -
3111		GENERATED_GBL_DATA_SIZE), and the initial stack is just
3112		below that area (growing from (CONFIG_SYS_INIT_RAM_ADDR +
3113		CONFIG_SYS_GBL_DATA_OFFSET) downward.
3114
3115	Note:
3116		On the MPC824X (or other systems that use the data
3117		cache for initial memory) the address chosen for
3118		CONFIG_SYS_INIT_RAM_ADDR is basically arbitrary - it must
3119		point to an otherwise UNUSED address space between
3120		the top of RAM and the start of the PCI space.
3121
3122- CONFIG_SYS_SCCR:	System Clock and reset Control Register (15-27)
3123
3124- CONFIG_SYS_OR_TIMING_SDRAM:
3125		SDRAM timing
3126
3127- CONFIG_SYS_MAMR_PTA:
3128		periodic timer for refresh
3129
3130- FLASH_BASE0_PRELIM, FLASH_BASE1_PRELIM, CONFIG_SYS_REMAP_OR_AM,
3131  CONFIG_SYS_PRELIM_OR_AM, CONFIG_SYS_OR_TIMING_FLASH, CONFIG_SYS_OR0_REMAP,
3132  CONFIG_SYS_OR0_PRELIM, CONFIG_SYS_BR0_PRELIM, CONFIG_SYS_OR1_REMAP, CONFIG_SYS_OR1_PRELIM,
3133  CONFIG_SYS_BR1_PRELIM:
3134		Memory Controller Definitions: BR0/1 and OR0/1 (FLASH)
3135
3136- SDRAM_BASE2_PRELIM, SDRAM_BASE3_PRELIM, SDRAM_MAX_SIZE,
3137  CONFIG_SYS_OR_TIMING_SDRAM, CONFIG_SYS_OR2_PRELIM, CONFIG_SYS_BR2_PRELIM,
3138  CONFIG_SYS_OR3_PRELIM, CONFIG_SYS_BR3_PRELIM:
3139		Memory Controller Definitions: BR2/3 and OR2/3 (SDRAM)
3140
3141- CONFIG_PCI_ENUM_ONLY
3142		Only scan through and get the devices on the buses.
3143		Don't do any setup work, presumably because someone or
3144		something has already done it, and we don't need to do it
3145		a second time.	Useful for platforms that are pre-booted
3146		by coreboot or similar.
3147
3148- CONFIG_PCI_INDIRECT_BRIDGE:
3149		Enable support for indirect PCI bridges.
3150
3151- CONFIG_SYS_SRIO:
3152		Chip has SRIO or not
3153
3154- CONFIG_SRIO1:
3155		Board has SRIO 1 port available
3156
3157- CONFIG_SRIO2:
3158		Board has SRIO 2 port available
3159
3160- CONFIG_SRIO_PCIE_BOOT_MASTER
3161		Board can support master function for Boot from SRIO and PCIE
3162
3163- CONFIG_SYS_SRIOn_MEM_VIRT:
3164		Virtual Address of SRIO port 'n' memory region
3165
3166- CONFIG_SYS_SRIOn_MEM_PHYS:
3167		Physical Address of SRIO port 'n' memory region
3168
3169- CONFIG_SYS_SRIOn_MEM_SIZE:
3170		Size of SRIO port 'n' memory region
3171
3172- CONFIG_SYS_NAND_BUSWIDTH_16BIT
3173		Defined to tell the NAND controller that the NAND chip is using
3174		a 16 bit bus.
3175		Not all NAND drivers use this symbol.
3176		Example of drivers that use it:
3177		- drivers/mtd/nand/raw/ndfc.c
3178		- drivers/mtd/nand/raw/mxc_nand.c
3179
3180- CONFIG_SYS_NDFC_EBC0_CFG
3181		Sets the EBC0_CFG register for the NDFC. If not defined
3182		a default value will be used.
3183
3184- CONFIG_SPD_EEPROM
3185		Get DDR timing information from an I2C EEPROM. Common
3186		with pluggable memory modules such as SODIMMs
3187
3188  SPD_EEPROM_ADDRESS
3189		I2C address of the SPD EEPROM
3190
3191- CONFIG_SYS_SPD_BUS_NUM
3192		If SPD EEPROM is on an I2C bus other than the first
3193		one, specify here. Note that the value must resolve
3194		to something your driver can deal with.
3195
3196- CONFIG_SYS_DDR_RAW_TIMING
3197		Get DDR timing information from other than SPD. Common with
3198		soldered DDR chips onboard without SPD. DDR raw timing
3199		parameters are extracted from datasheet and hard-coded into
3200		header files or board specific files.
3201
3202- CONFIG_FSL_DDR_INTERACTIVE
3203		Enable interactive DDR debugging. See doc/README.fsl-ddr.
3204
3205- CONFIG_FSL_DDR_SYNC_REFRESH
3206		Enable sync of refresh for multiple controllers.
3207
3208- CONFIG_FSL_DDR_BIST
3209		Enable built-in memory test for Freescale DDR controllers.
3210
3211- CONFIG_SYS_83XX_DDR_USES_CS0
3212		Only for 83xx systems. If specified, then DDR should
3213		be configured using CS0 and CS1 instead of CS2 and CS3.
3214
3215- CONFIG_RMII
3216		Enable RMII mode for all FECs.
3217		Note that this is a global option, we can't
3218		have one FEC in standard MII mode and another in RMII mode.
3219
3220- CONFIG_CRC32_VERIFY
3221		Add a verify option to the crc32 command.
3222		The syntax is:
3223
3224		=> crc32 -v <address> <count> <crc32>
3225
3226		Where address/count indicate a memory area
3227		and crc32 is the correct crc32 which the
3228		area should have.
3229
3230- CONFIG_LOOPW
3231		Add the "loopw" memory command. This only takes effect if
3232		the memory commands are activated globally (CONFIG_CMD_MEMORY).
3233
3234- CONFIG_MX_CYCLIC
3235		Add the "mdc" and "mwc" memory commands. These are cyclic
3236		"md/mw" commands.
3237		Examples:
3238
3239		=> mdc.b 10 4 500
3240		This command will print 4 bytes (10,11,12,13) each 500 ms.
3241
3242		=> mwc.l 100 12345678 10
3243		This command will write 12345678 to address 100 all 10 ms.
3244
3245		This only takes effect if the memory commands are activated
3246		globally (CONFIG_CMD_MEMORY).
3247
3248- CONFIG_SKIP_LOWLEVEL_INIT
3249		[ARM, NDS32, MIPS, RISC-V only] If this variable is defined, then certain
3250		low level initializations (like setting up the memory
3251		controller) are omitted and/or U-Boot does not
3252		relocate itself into RAM.
3253
3254		Normally this variable MUST NOT be defined. The only
3255		exception is when U-Boot is loaded (to RAM) by some
3256		other boot loader or by a debugger which performs
3257		these initializations itself.
3258
3259- CONFIG_SKIP_LOWLEVEL_INIT_ONLY
3260		[ARM926EJ-S only] This allows just the call to lowlevel_init()
3261		to be skipped. The normal CP15 init (such as enabling the
3262		instruction cache) is still performed.
3263
3264- CONFIG_SPL_BUILD
3265		Modifies the behaviour of start.S when compiling a loader
3266		that is executed before the actual U-Boot. E.g. when
3267		compiling a NAND SPL.
3268
3269- CONFIG_TPL_BUILD
3270		Modifies the behaviour of start.S  when compiling a loader
3271		that is executed after the SPL and before the actual U-Boot.
3272		It is loaded by the SPL.
3273
3274- CONFIG_SYS_MPC85XX_NO_RESETVEC
3275		Only for 85xx systems. If this variable is specified, the section
3276		.resetvec is not kept and the section .bootpg is placed in the
3277		previous 4k of the .text section.
3278
3279- CONFIG_ARCH_MAP_SYSMEM
3280		Generally U-Boot (and in particular the md command) uses
3281		effective address. It is therefore not necessary to regard
3282		U-Boot address as virtual addresses that need to be translated
3283		to physical addresses. However, sandbox requires this, since
3284		it maintains its own little RAM buffer which contains all
3285		addressable memory. This option causes some memory accesses
3286		to be mapped through map_sysmem() / unmap_sysmem().
3287
3288- CONFIG_X86_RESET_VECTOR
3289		If defined, the x86 reset vector code is included. This is not
3290		needed when U-Boot is running from Coreboot.
3291
3292- CONFIG_SYS_NAND_NO_SUBPAGE_WRITE
3293		Option to disable subpage write in NAND driver
3294		driver that uses this:
3295		drivers/mtd/nand/raw/davinci_nand.c
3296
3297Freescale QE/FMAN Firmware Support:
3298-----------------------------------
3299
3300The Freescale QUICCEngine (QE) and Frame Manager (FMAN) both support the
3301loading of "firmware", which is encoded in the QE firmware binary format.
3302This firmware often needs to be loaded during U-Boot booting, so macros
3303are used to identify the storage device (NOR flash, SPI, etc) and the address
3304within that device.
3305
3306- CONFIG_SYS_FMAN_FW_ADDR
3307	The address in the storage device where the FMAN microcode is located.  The
3308	meaning of this address depends on which CONFIG_SYS_QE_FW_IN_xxx macro
3309	is also specified.
3310
3311- CONFIG_SYS_QE_FW_ADDR
3312	The address in the storage device where the QE microcode is located.  The
3313	meaning of this address depends on which CONFIG_SYS_QE_FW_IN_xxx macro
3314	is also specified.
3315
3316- CONFIG_SYS_QE_FMAN_FW_LENGTH
3317	The maximum possible size of the firmware.  The firmware binary format
3318	has a field that specifies the actual size of the firmware, but it
3319	might not be possible to read any part of the firmware unless some
3320	local storage is allocated to hold the entire firmware first.
3321
3322- CONFIG_SYS_QE_FMAN_FW_IN_NOR
3323	Specifies that QE/FMAN firmware is located in NOR flash, mapped as
3324	normal addressable memory via the LBC.  CONFIG_SYS_FMAN_FW_ADDR is the
3325	virtual address in NOR flash.
3326
3327- CONFIG_SYS_QE_FMAN_FW_IN_NAND
3328	Specifies that QE/FMAN firmware is located in NAND flash.
3329	CONFIG_SYS_FMAN_FW_ADDR is the offset within NAND flash.
3330
3331- CONFIG_SYS_QE_FMAN_FW_IN_MMC
3332	Specifies that QE/FMAN firmware is located on the primary SD/MMC
3333	device.  CONFIG_SYS_FMAN_FW_ADDR is the byte offset on that device.
3334
3335- CONFIG_SYS_QE_FMAN_FW_IN_REMOTE
3336	Specifies that QE/FMAN firmware is located in the remote (master)
3337	memory space.	CONFIG_SYS_FMAN_FW_ADDR is a virtual address which
3338	can be mapped from slave TLB->slave LAW->slave SRIO or PCIE outbound
3339	window->master inbound window->master LAW->the ucode address in
3340	master's memory space.
3341
3342Freescale Layerscape Management Complex Firmware Support:
3343---------------------------------------------------------
3344The Freescale Layerscape Management Complex (MC) supports the loading of
3345"firmware".
3346This firmware often needs to be loaded during U-Boot booting, so macros
3347are used to identify the storage device (NOR flash, SPI, etc) and the address
3348within that device.
3349
3350- CONFIG_FSL_MC_ENET
3351	Enable the MC driver for Layerscape SoCs.
3352
3353Freescale Layerscape Debug Server Support:
3354-------------------------------------------
3355The Freescale Layerscape Debug Server Support supports the loading of
3356"Debug Server firmware" and triggering SP boot-rom.
3357This firmware often needs to be loaded during U-Boot booting.
3358
3359- CONFIG_SYS_MC_RSV_MEM_ALIGN
3360	Define alignment of reserved memory MC requires
3361
3362Reproducible builds
3363-------------------
3364
3365In order to achieve reproducible builds, timestamps used in the U-Boot build
3366process have to be set to a fixed value.
3367
3368This is done using the SOURCE_DATE_EPOCH environment variable.
3369SOURCE_DATE_EPOCH is to be set on the build host's shell, not as a configuration
3370option for U-Boot or an environment variable in U-Boot.
3371
3372SOURCE_DATE_EPOCH should be set to a number of seconds since the epoch, in UTC.
3373
3374Building the Software:
3375======================
3376
3377Building U-Boot has been tested in several native build environments
3378and in many different cross environments. Of course we cannot support
3379all possibly existing versions of cross development tools in all
3380(potentially obsolete) versions. In case of tool chain problems we
3381recommend to use the ELDK (see http://www.denx.de/wiki/DULG/ELDK)
3382which is extensively used to build and test U-Boot.
3383
3384If you are not using a native environment, it is assumed that you
3385have GNU cross compiling tools available in your path. In this case,
3386you must set the environment variable CROSS_COMPILE in your shell.
3387Note that no changes to the Makefile or any other source files are
3388necessary. For example using the ELDK on a 4xx CPU, please enter:
3389
3390	$ CROSS_COMPILE=ppc_4xx-
3391	$ export CROSS_COMPILE
3392
3393Note: If you wish to generate Windows versions of the utilities in
3394      the tools directory you can use the MinGW toolchain
3395      (http://www.mingw.org).  Set your HOST tools to the MinGW
3396      toolchain and execute 'make tools'.  For example:
3397
3398       $ make HOSTCC=i586-mingw32msvc-gcc HOSTSTRIP=i586-mingw32msvc-strip tools
3399
3400      Binaries such as tools/mkimage.exe will be created which can
3401      be executed on computers running Windows.
3402
3403U-Boot is intended to be simple to build. After installing the
3404sources you must configure U-Boot for one specific board type. This
3405is done by typing:
3406
3407	make NAME_defconfig
3408
3409where "NAME_defconfig" is the name of one of the existing configu-
3410rations; see boards.cfg for supported names.
3411
3412Note: for some board special configuration names may exist; check if
3413      additional information is available from the board vendor; for
3414      instance, the TQM823L systems are available without (standard)
3415      or with LCD support. You can select such additional "features"
3416      when choosing the configuration, i. e.
3417
3418      make TQM823L_defconfig
3419	- will configure for a plain TQM823L, i. e. no LCD support
3420
3421      make TQM823L_LCD_defconfig
3422	- will configure for a TQM823L with U-Boot console on LCD
3423
3424      etc.
3425
3426
3427Finally, type "make all", and you should get some working U-Boot
3428images ready for download to / installation on your system:
3429
3430- "u-boot.bin" is a raw binary image
3431- "u-boot" is an image in ELF binary format
3432- "u-boot.srec" is in Motorola S-Record format
3433
3434By default the build is performed locally and the objects are saved
3435in the source directory. One of the two methods can be used to change
3436this behavior and build U-Boot to some external directory:
3437
34381. Add O= to the make command line invocations:
3439
3440	make O=/tmp/build distclean
3441	make O=/tmp/build NAME_defconfig
3442	make O=/tmp/build all
3443
34442. Set environment variable KBUILD_OUTPUT to point to the desired location:
3445
3446	export KBUILD_OUTPUT=/tmp/build
3447	make distclean
3448	make NAME_defconfig
3449	make all
3450
3451Note that the command line "O=" setting overrides the KBUILD_OUTPUT environment
3452variable.
3453
3454User specific CPPFLAGS, AFLAGS and CFLAGS can be passed to the compiler by
3455setting the according environment variables KCPPFLAGS, KAFLAGS and KCFLAGS.
3456For example to treat all compiler warnings as errors:
3457
3458	make KCFLAGS=-Werror
3459
3460Please be aware that the Makefiles assume you are using GNU make, so
3461for instance on NetBSD you might need to use "gmake" instead of
3462native "make".
3463
3464
3465If the system board that you have is not listed, then you will need
3466to port U-Boot to your hardware platform. To do this, follow these
3467steps:
3468
34691.  Create a new directory to hold your board specific code. Add any
3470    files you need. In your board directory, you will need at least
3471    the "Makefile" and a "<board>.c".
34722.  Create a new configuration file "include/configs/<board>.h" for
3473    your board.
34743.  If you're porting U-Boot to a new CPU, then also create a new
3475    directory to hold your CPU specific code. Add any files you need.
34764.  Run "make <board>_defconfig" with your new name.
34775.  Type "make", and you should get a working "u-boot.srec" file
3478    to be installed on your target system.
34796.  Debug and solve any problems that might arise.
3480    [Of course, this last step is much harder than it sounds.]
3481
3482
3483Testing of U-Boot Modifications, Ports to New Hardware, etc.:
3484==============================================================
3485
3486If you have modified U-Boot sources (for instance added a new board
3487or support for new devices, a new CPU, etc.) you are expected to
3488provide feedback to the other developers. The feedback normally takes
3489the form of a "patch", i. e. a context diff against a certain (latest
3490official or latest in the git repository) version of U-Boot sources.
3491
3492But before you submit such a patch, please verify that your modifi-
3493cation did not break existing code. At least make sure that *ALL* of
3494the supported boards compile WITHOUT ANY compiler warnings. To do so,
3495just run the buildman script (tools/buildman/buildman), which will
3496configure and build U-Boot for ALL supported system. Be warned, this
3497will take a while. Please see the buildman README, or run 'buildman -H'
3498for documentation.
3499
3500
3501See also "U-Boot Porting Guide" below.
3502
3503
3504Monitor Commands - Overview:
3505============================
3506
3507go	- start application at address 'addr'
3508run	- run commands in an environment variable
3509bootm	- boot application image from memory
3510bootp	- boot image via network using BootP/TFTP protocol
3511bootz   - boot zImage from memory
3512tftpboot- boot image via network using TFTP protocol
3513	       and env variables "ipaddr" and "serverip"
3514	       (and eventually "gatewayip")
3515tftpput - upload a file via network using TFTP protocol
3516rarpboot- boot image via network using RARP/TFTP protocol
3517diskboot- boot from IDE devicebootd   - boot default, i.e., run 'bootcmd'
3518loads	- load S-Record file over serial line
3519loadb	- load binary file over serial line (kermit mode)
3520md	- memory display
3521mm	- memory modify (auto-incrementing)
3522nm	- memory modify (constant address)
3523mw	- memory write (fill)
3524cp	- memory copy
3525cmp	- memory compare
3526crc32	- checksum calculation
3527i2c	- I2C sub-system
3528sspi	- SPI utility commands
3529base	- print or set address offset
3530printenv- print environment variables
3531setenv	- set environment variables
3532saveenv - save environment variables to persistent storage
3533protect - enable or disable FLASH write protection
3534erase	- erase FLASH memory
3535flinfo	- print FLASH memory information
3536nand	- NAND memory operations (see doc/README.nand)
3537bdinfo	- print Board Info structure
3538iminfo	- print header information for application image
3539coninfo - print console devices and informations
3540ide	- IDE sub-system
3541loop	- infinite loop on address range
3542loopw	- infinite write loop on address range
3543mtest	- simple RAM test
3544icache	- enable or disable instruction cache
3545dcache	- enable or disable data cache
3546reset	- Perform RESET of the CPU
3547echo	- echo args to console
3548version - print monitor version
3549help	- print online help
3550?	- alias for 'help'
3551
3552
3553Monitor Commands - Detailed Description:
3554========================================
3555
3556TODO.
3557
3558For now: just type "help <command>".
3559
3560
3561Environment Variables:
3562======================
3563
3564U-Boot supports user configuration using Environment Variables which
3565can be made persistent by saving to Flash memory.
3566
3567Environment Variables are set using "setenv", printed using
3568"printenv", and saved to Flash using "saveenv". Using "setenv"
3569without a value can be used to delete a variable from the
3570environment. As long as you don't save the environment you are
3571working with an in-memory copy. In case the Flash area containing the
3572environment is erased by accident, a default environment is provided.
3573
3574Some configuration options can be set using Environment Variables.
3575
3576List of environment variables (most likely not complete):
3577
3578  baudrate	- see CONFIG_BAUDRATE
3579
3580  bootdelay	- see CONFIG_BOOTDELAY
3581
3582  bootcmd	- see CONFIG_BOOTCOMMAND
3583
3584  bootargs	- Boot arguments when booting an RTOS image
3585
3586  bootfile	- Name of the image to load with TFTP
3587
3588  bootm_low	- Memory range available for image processing in the bootm
3589		  command can be restricted. This variable is given as
3590		  a hexadecimal number and defines lowest address allowed
3591		  for use by the bootm command. See also "bootm_size"
3592		  environment variable. Address defined by "bootm_low" is
3593		  also the base of the initial memory mapping for the Linux
3594		  kernel -- see the description of CONFIG_SYS_BOOTMAPSZ and
3595		  bootm_mapsize.
3596
3597  bootm_mapsize - Size of the initial memory mapping for the Linux kernel.
3598		  This variable is given as a hexadecimal number and it
3599		  defines the size of the memory region starting at base
3600		  address bootm_low that is accessible by the Linux kernel
3601		  during early boot.  If unset, CONFIG_SYS_BOOTMAPSZ is used
3602		  as the default value if it is defined, and bootm_size is
3603		  used otherwise.
3604
3605  bootm_size	- Memory range available for image processing in the bootm
3606		  command can be restricted. This variable is given as
3607		  a hexadecimal number and defines the size of the region
3608		  allowed for use by the bootm command. See also "bootm_low"
3609		  environment variable.
3610
3611  updatefile	- Location of the software update file on a TFTP server, used
3612		  by the automatic software update feature. Please refer to
3613		  documentation in doc/README.update for more details.
3614
3615  autoload	- if set to "no" (any string beginning with 'n'),
3616		  "bootp" will just load perform a lookup of the
3617		  configuration from the BOOTP server, but not try to
3618		  load any image using TFTP
3619
3620  autostart	- if set to "yes", an image loaded using the "bootp",
3621		  "rarpboot", "tftpboot" or "diskboot" commands will
3622		  be automatically started (by internally calling
3623		  "bootm")
3624
3625		  If set to "no", a standalone image passed to the
3626		  "bootm" command will be copied to the load address
3627		  (and eventually uncompressed), but NOT be started.
3628		  This can be used to load and uncompress arbitrary
3629		  data.
3630
3631  fdt_high	- if set this restricts the maximum address that the
3632		  flattened device tree will be copied into upon boot.
3633		  For example, if you have a system with 1 GB memory
3634		  at physical address 0x10000000, while Linux kernel
3635		  only recognizes the first 704 MB as low memory, you
3636		  may need to set fdt_high as 0x3C000000 to have the
3637		  device tree blob be copied to the maximum address
3638		  of the 704 MB low memory, so that Linux kernel can
3639		  access it during the boot procedure.
3640
3641		  If this is set to the special value 0xFFFFFFFF then
3642		  the fdt will not be copied at all on boot.  For this
3643		  to work it must reside in writable memory, have
3644		  sufficient padding on the end of it for u-boot to
3645		  add the information it needs into it, and the memory
3646		  must be accessible by the kernel.
3647
3648  fdtcontroladdr- if set this is the address of the control flattened
3649		  device tree used by U-Boot when CONFIG_OF_CONTROL is
3650		  defined.
3651
3652  i2cfast	- (PPC405GP|PPC405EP only)
3653		  if set to 'y' configures Linux I2C driver for fast
3654		  mode (400kHZ). This environment variable is used in
3655		  initialization code. So, for changes to be effective
3656		  it must be saved and board must be reset.
3657
3658  initrd_high	- restrict positioning of initrd images:
3659		  If this variable is not set, initrd images will be
3660		  copied to the highest possible address in RAM; this
3661		  is usually what you want since it allows for
3662		  maximum initrd size. If for some reason you want to
3663		  make sure that the initrd image is loaded below the
3664		  CONFIG_SYS_BOOTMAPSZ limit, you can set this environment
3665		  variable to a value of "no" or "off" or "0".
3666		  Alternatively, you can set it to a maximum upper
3667		  address to use (U-Boot will still check that it
3668		  does not overwrite the U-Boot stack and data).
3669
3670		  For instance, when you have a system with 16 MB
3671		  RAM, and want to reserve 4 MB from use by Linux,
3672		  you can do this by adding "mem=12M" to the value of
3673		  the "bootargs" variable. However, now you must make
3674		  sure that the initrd image is placed in the first
3675		  12 MB as well - this can be done with
3676
3677		  setenv initrd_high 00c00000
3678
3679		  If you set initrd_high to 0xFFFFFFFF, this is an
3680		  indication to U-Boot that all addresses are legal
3681		  for the Linux kernel, including addresses in flash
3682		  memory. In this case U-Boot will NOT COPY the
3683		  ramdisk at all. This may be useful to reduce the
3684		  boot time on your system, but requires that this
3685		  feature is supported by your Linux kernel.
3686
3687  ipaddr	- IP address; needed for tftpboot command
3688
3689  loadaddr	- Default load address for commands like "bootp",
3690		  "rarpboot", "tftpboot", "loadb" or "diskboot"
3691
3692  loads_echo	- see CONFIG_LOADS_ECHO
3693
3694  serverip	- TFTP server IP address; needed for tftpboot command
3695
3696  bootretry	- see CONFIG_BOOT_RETRY_TIME
3697
3698  bootdelaykey	- see CONFIG_AUTOBOOT_DELAY_STR
3699
3700  bootstopkey	- see CONFIG_AUTOBOOT_STOP_STR
3701
3702  ethprime	- controls which interface is used first.
3703
3704  ethact	- controls which interface is currently active.
3705		  For example you can do the following
3706
3707		  => setenv ethact FEC
3708		  => ping 192.168.0.1 # traffic sent on FEC
3709		  => setenv ethact SCC
3710		  => ping 10.0.0.1 # traffic sent on SCC
3711
3712  ethrotate	- When set to "no" U-Boot does not go through all
3713		  available network interfaces.
3714		  It just stays at the currently selected interface.
3715
3716  netretry	- When set to "no" each network operation will
3717		  either succeed or fail without retrying.
3718		  When set to "once" the network operation will
3719		  fail when all the available network interfaces
3720		  are tried once without success.
3721		  Useful on scripts which control the retry operation
3722		  themselves.
3723
3724  npe_ucode	- set load address for the NPE microcode
3725
3726  silent_linux  - If set then Linux will be told to boot silently, by
3727		  changing the console to be empty. If "yes" it will be
3728		  made silent. If "no" it will not be made silent. If
3729		  unset, then it will be made silent if the U-Boot console
3730		  is silent.
3731
3732  tftpsrcp	- If this is set, the value is used for TFTP's
3733		  UDP source port.
3734
3735  tftpdstp	- If this is set, the value is used for TFTP's UDP
3736		  destination port instead of the Well Know Port 69.
3737
3738  tftpblocksize - Block size to use for TFTP transfers; if not set,
3739		  we use the TFTP server's default block size
3740
3741  tftptimeout	- Retransmission timeout for TFTP packets (in milli-
3742		  seconds, minimum value is 1000 = 1 second). Defines
3743		  when a packet is considered to be lost so it has to
3744		  be retransmitted. The default is 5000 = 5 seconds.
3745		  Lowering this value may make downloads succeed
3746		  faster in networks with high packet loss rates or
3747		  with unreliable TFTP servers.
3748
3749  tftptimeoutcountmax	- maximum count of TFTP timeouts (no
3750		  unit, minimum value = 0). Defines how many timeouts
3751		  can happen during a single file transfer before that
3752		  transfer is aborted. The default is 10, and 0 means
3753		  'no timeouts allowed'. Increasing this value may help
3754		  downloads succeed with high packet loss rates, or with
3755		  unreliable TFTP servers or client hardware.
3756
3757  vlan		- When set to a value < 4095 the traffic over
3758		  Ethernet is encapsulated/received over 802.1q
3759		  VLAN tagged frames.
3760
3761  bootpretryperiod	- Period during which BOOTP/DHCP sends retries.
3762		  Unsigned value, in milliseconds. If not set, the period will
3763		  be either the default (28000), or a value based on
3764		  CONFIG_NET_RETRY_COUNT, if defined. This value has
3765		  precedence over the valu based on CONFIG_NET_RETRY_COUNT.
3766
3767The following image location variables contain the location of images
3768used in booting. The "Image" column gives the role of the image and is
3769not an environment variable name. The other columns are environment
3770variable names. "File Name" gives the name of the file on a TFTP
3771server, "RAM Address" gives the location in RAM the image will be
3772loaded to, and "Flash Location" gives the image's address in NOR
3773flash or offset in NAND flash.
3774
3775*Note* - these variables don't have to be defined for all boards, some
3776boards currently use other variables for these purposes, and some
3777boards use these variables for other purposes.
3778
3779Image		    File Name	     RAM Address       Flash Location
3780-----		    ---------	     -----------       --------------
3781u-boot		    u-boot	     u-boot_addr_r     u-boot_addr
3782Linux kernel	    bootfile	     kernel_addr_r     kernel_addr
3783device tree blob    fdtfile	     fdt_addr_r	       fdt_addr
3784ramdisk		    ramdiskfile	     ramdisk_addr_r    ramdisk_addr
3785
3786The following environment variables may be used and automatically
3787updated by the network boot commands ("bootp" and "rarpboot"),
3788depending the information provided by your boot server:
3789
3790  bootfile	- see above
3791  dnsip		- IP address of your Domain Name Server
3792  dnsip2	- IP address of your secondary Domain Name Server
3793  gatewayip	- IP address of the Gateway (Router) to use
3794  hostname	- Target hostname
3795  ipaddr	- see above
3796  netmask	- Subnet Mask
3797  rootpath	- Pathname of the root filesystem on the NFS server
3798  serverip	- see above
3799
3800
3801There are two special Environment Variables:
3802
3803  serial#	- contains hardware identification information such
3804		  as type string and/or serial number
3805  ethaddr	- Ethernet address
3806
3807These variables can be set only once (usually during manufacturing of
3808the board). U-Boot refuses to delete or overwrite these variables
3809once they have been set once.
3810
3811
3812Further special Environment Variables:
3813
3814  ver		- Contains the U-Boot version string as printed
3815		  with the "version" command. This variable is
3816		  readonly (see CONFIG_VERSION_VARIABLE).
3817
3818
3819Please note that changes to some configuration parameters may take
3820only effect after the next boot (yes, that's just like Windoze :-).
3821
3822
3823Callback functions for environment variables:
3824---------------------------------------------
3825
3826For some environment variables, the behavior of u-boot needs to change
3827when their values are changed.  This functionality allows functions to
3828be associated with arbitrary variables.  On creation, overwrite, or
3829deletion, the callback will provide the opportunity for some side
3830effect to happen or for the change to be rejected.
3831
3832The callbacks are named and associated with a function using the
3833U_BOOT_ENV_CALLBACK macro in your board or driver code.
3834
3835These callbacks are associated with variables in one of two ways.  The
3836static list can be added to by defining CONFIG_ENV_CALLBACK_LIST_STATIC
3837in the board configuration to a string that defines a list of
3838associations.  The list must be in the following format:
3839
3840	entry = variable_name[:callback_name]
3841	list = entry[,list]
3842
3843If the callback name is not specified, then the callback is deleted.
3844Spaces are also allowed anywhere in the list.
3845
3846Callbacks can also be associated by defining the ".callbacks" variable
3847with the same list format above.  Any association in ".callbacks" will
3848override any association in the static list. You can define
3849CONFIG_ENV_CALLBACK_LIST_DEFAULT to a list (string) to define the
3850".callbacks" environment variable in the default or embedded environment.
3851
3852If CONFIG_REGEX is defined, the variable_name above is evaluated as a
3853regular expression. This allows multiple variables to be connected to
3854the same callback without explicitly listing them all out.
3855
3856The signature of the callback functions is:
3857
3858    int callback(const char *name, const char *value, enum env_op op, int flags)
3859
3860* name - changed environment variable
3861* value - new value of the environment variable
3862* op - operation (create, overwrite, or delete)
3863* flags - attributes of the environment variable change, see flags H_* in
3864  include/search.h
3865
3866The return value is 0 if the variable change is accepted and 1 otherwise.
3867
3868Command Line Parsing:
3869=====================
3870
3871There are two different command line parsers available with U-Boot:
3872the old "simple" one, and the much more powerful "hush" shell:
3873
3874Old, simple command line parser:
3875--------------------------------
3876
3877- supports environment variables (through setenv / saveenv commands)
3878- several commands on one line, separated by ';'
3879- variable substitution using "... ${name} ..." syntax
3880- special characters ('$', ';') can be escaped by prefixing with '\',
3881  for example:
3882	setenv bootcmd bootm \${address}
3883- You can also escape text by enclosing in single apostrophes, for example:
3884	setenv addip 'setenv bootargs $bootargs ip=$ipaddr:$serverip:$gatewayip:$netmask:$hostname::off'
3885
3886Hush shell:
3887-----------
3888
3889- similar to Bourne shell, with control structures like
3890  if...then...else...fi, for...do...done; while...do...done,
3891  until...do...done, ...
3892- supports environment ("global") variables (through setenv / saveenv
3893  commands) and local shell variables (through standard shell syntax
3894  "name=value"); only environment variables can be used with "run"
3895  command
3896
3897General rules:
3898--------------
3899
3900(1) If a command line (or an environment variable executed by a "run"
3901    command) contains several commands separated by semicolon, and
3902    one of these commands fails, then the remaining commands will be
3903    executed anyway.
3904
3905(2) If you execute several variables with one call to run (i. e.
3906    calling run with a list of variables as arguments), any failing
3907    command will cause "run" to terminate, i. e. the remaining
3908    variables are not executed.
3909
3910Note for Redundant Ethernet Interfaces:
3911=======================================
3912
3913Some boards come with redundant Ethernet interfaces; U-Boot supports
3914such configurations and is capable of automatic selection of a
3915"working" interface when needed. MAC assignment works as follows:
3916
3917Network interfaces are numbered eth0, eth1, eth2, ... Corresponding
3918MAC addresses can be stored in the environment as "ethaddr" (=>eth0),
3919"eth1addr" (=>eth1), "eth2addr", ...
3920
3921If the network interface stores some valid MAC address (for instance
3922in SROM), this is used as default address if there is NO correspon-
3923ding setting in the environment; if the corresponding environment
3924variable is set, this overrides the settings in the card; that means:
3925
3926o If the SROM has a valid MAC address, and there is no address in the
3927  environment, the SROM's address is used.
3928
3929o If there is no valid address in the SROM, and a definition in the
3930  environment exists, then the value from the environment variable is
3931  used.
3932
3933o If both the SROM and the environment contain a MAC address, and
3934  both addresses are the same, this MAC address is used.
3935
3936o If both the SROM and the environment contain a MAC address, and the
3937  addresses differ, the value from the environment is used and a
3938  warning is printed.
3939
3940o If neither SROM nor the environment contain a MAC address, an error
3941  is raised. If CONFIG_NET_RANDOM_ETHADDR is defined, then in this case
3942  a random, locally-assigned MAC is used.
3943
3944If Ethernet drivers implement the 'write_hwaddr' function, valid MAC addresses
3945will be programmed into hardware as part of the initialization process.	 This
3946may be skipped by setting the appropriate 'ethmacskip' environment variable.
3947The naming convention is as follows:
3948"ethmacskip" (=>eth0), "eth1macskip" (=>eth1) etc.
3949
3950Image Formats:
3951==============
3952
3953U-Boot is capable of booting (and performing other auxiliary operations on)
3954images in two formats:
3955
3956New uImage format (FIT)
3957-----------------------
3958
3959Flexible and powerful format based on Flattened Image Tree -- FIT (similar
3960to Flattened Device Tree). It allows the use of images with multiple
3961components (several kernels, ramdisks, etc.), with contents protected by
3962SHA1, MD5 or CRC32. More details are found in the doc/uImage.FIT directory.
3963
3964
3965Old uImage format
3966-----------------
3967
3968Old image format is based on binary files which can be basically anything,
3969preceded by a special header; see the definitions in include/image.h for
3970details; basically, the header defines the following image properties:
3971
3972* Target Operating System (Provisions for OpenBSD, NetBSD, FreeBSD,
3973  4.4BSD, Linux, SVR4, Esix, Solaris, Irix, SCO, Dell, NCR, VxWorks,
3974  LynxOS, pSOS, QNX, RTEMS, INTEGRITY;
3975  Currently supported: Linux, NetBSD, VxWorks, QNX, RTEMS, LynxOS,
3976  INTEGRITY).
3977* Target CPU Architecture (Provisions for Alpha, ARM, Intel x86,
3978  IA64, MIPS, NDS32, Nios II, PowerPC, IBM S390, SuperH, Sparc, Sparc 64 Bit;
3979  Currently supported: ARM, Intel x86, MIPS, NDS32, Nios II, PowerPC).
3980* Compression Type (uncompressed, gzip, bzip2)
3981* Load Address
3982* Entry Point
3983* Image Name
3984* Image Timestamp
3985
3986The header is marked by a special Magic Number, and both the header
3987and the data portions of the image are secured against corruption by
3988CRC32 checksums.
3989
3990
3991Linux Support:
3992==============
3993
3994Although U-Boot should support any OS or standalone application
3995easily, the main focus has always been on Linux during the design of
3996U-Boot.
3997
3998U-Boot includes many features that so far have been part of some
3999special "boot loader" code within the Linux kernel. Also, any
4000"initrd" images to be used are no longer part of one big Linux image;
4001instead, kernel and "initrd" are separate images. This implementation
4002serves several purposes:
4003
4004- the same features can be used for other OS or standalone
4005  applications (for instance: using compressed images to reduce the
4006  Flash memory footprint)
4007
4008- it becomes much easier to port new Linux kernel versions because
4009  lots of low-level, hardware dependent stuff are done by U-Boot
4010
4011- the same Linux kernel image can now be used with different "initrd"
4012  images; of course this also means that different kernel images can
4013  be run with the same "initrd". This makes testing easier (you don't
4014  have to build a new "zImage.initrd" Linux image when you just
4015  change a file in your "initrd"). Also, a field-upgrade of the
4016  software is easier now.
4017
4018
4019Linux HOWTO:
4020============
4021
4022Porting Linux to U-Boot based systems:
4023---------------------------------------
4024
4025U-Boot cannot save you from doing all the necessary modifications to
4026configure the Linux device drivers for use with your target hardware
4027(no, we don't intend to provide a full virtual machine interface to
4028Linux :-).
4029
4030But now you can ignore ALL boot loader code (in arch/powerpc/mbxboot).
4031
4032Just make sure your machine specific header file (for instance
4033include/asm-ppc/tqm8xx.h) includes the same definition of the Board
4034Information structure as we define in include/asm-<arch>/u-boot.h,
4035and make sure that your definition of IMAP_ADDR uses the same value
4036as your U-Boot configuration in CONFIG_SYS_IMMR.
4037
4038Note that U-Boot now has a driver model, a unified model for drivers.
4039If you are adding a new driver, plumb it into driver model. If there
4040is no uclass available, you are encouraged to create one. See
4041doc/driver-model.
4042
4043
4044Configuring the Linux kernel:
4045-----------------------------
4046
4047No specific requirements for U-Boot. Make sure you have some root
4048device (initial ramdisk, NFS) for your target system.
4049
4050
4051Building a Linux Image:
4052-----------------------
4053
4054With U-Boot, "normal" build targets like "zImage" or "bzImage" are
4055not used. If you use recent kernel source, a new build target
4056"uImage" will exist which automatically builds an image usable by
4057U-Boot. Most older kernels also have support for a "pImage" target,
4058which was introduced for our predecessor project PPCBoot and uses a
4059100% compatible format.
4060
4061Example:
4062
4063	make TQM850L_defconfig
4064	make oldconfig
4065	make dep
4066	make uImage
4067
4068The "uImage" build target uses a special tool (in 'tools/mkimage') to
4069encapsulate a compressed Linux kernel image with header	 information,
4070CRC32 checksum etc. for use with U-Boot. This is what we are doing:
4071
4072* build a standard "vmlinux" kernel image (in ELF binary format):
4073
4074* convert the kernel into a raw binary image:
4075
4076	${CROSS_COMPILE}-objcopy -O binary \
4077				 -R .note -R .comment \
4078				 -S vmlinux linux.bin
4079
4080* compress the binary image:
4081
4082	gzip -9 linux.bin
4083
4084* package compressed binary image for U-Boot:
4085
4086	mkimage -A ppc -O linux -T kernel -C gzip \
4087		-a 0 -e 0 -n "Linux Kernel Image" \
4088		-d linux.bin.gz uImage
4089
4090
4091The "mkimage" tool can also be used to create ramdisk images for use
4092with U-Boot, either separated from the Linux kernel image, or
4093combined into one file. "mkimage" encapsulates the images with a 64
4094byte header containing information about target architecture,
4095operating system, image type, compression method, entry points, time
4096stamp, CRC32 checksums, etc.
4097
4098"mkimage" can be called in two ways: to verify existing images and
4099print the header information, or to build new images.
4100
4101In the first form (with "-l" option) mkimage lists the information
4102contained in the header of an existing U-Boot image; this includes
4103checksum verification:
4104
4105	tools/mkimage -l image
4106	  -l ==> list image header information
4107
4108The second form (with "-d" option) is used to build a U-Boot image
4109from a "data file" which is used as image payload:
4110
4111	tools/mkimage -A arch -O os -T type -C comp -a addr -e ep \
4112		      -n name -d data_file image
4113	  -A ==> set architecture to 'arch'
4114	  -O ==> set operating system to 'os'
4115	  -T ==> set image type to 'type'
4116	  -C ==> set compression type 'comp'
4117	  -a ==> set load address to 'addr' (hex)
4118	  -e ==> set entry point to 'ep' (hex)
4119	  -n ==> set image name to 'name'
4120	  -d ==> use image data from 'datafile'
4121
4122Right now, all Linux kernels for PowerPC systems use the same load
4123address (0x00000000), but the entry point address depends on the
4124kernel version:
4125
4126- 2.2.x kernels have the entry point at 0x0000000C,
4127- 2.3.x and later kernels have the entry point at 0x00000000.
4128
4129So a typical call to build a U-Boot image would read:
4130
4131	-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
4132	> -A ppc -O linux -T kernel -C gzip -a 0 -e 0 \
4133	> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz \
4134	> examples/uImage.TQM850L
4135	Image Name:   2.4.4 kernel for TQM850L
4136	Created:      Wed Jul 19 02:34:59 2000
4137	Image Type:   PowerPC Linux Kernel Image (gzip compressed)
4138	Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
4139	Load Address: 0x00000000
4140	Entry Point:  0x00000000
4141
4142To verify the contents of the image (or check for corruption):
4143
4144	-> tools/mkimage -l examples/uImage.TQM850L
4145	Image Name:   2.4.4 kernel for TQM850L
4146	Created:      Wed Jul 19 02:34:59 2000
4147	Image Type:   PowerPC Linux Kernel Image (gzip compressed)
4148	Data Size:    335725 Bytes = 327.86 kB = 0.32 MB
4149	Load Address: 0x00000000
4150	Entry Point:  0x00000000
4151
4152NOTE: for embedded systems where boot time is critical you can trade
4153speed for memory and install an UNCOMPRESSED image instead: this
4154needs more space in Flash, but boots much faster since it does not
4155need to be uncompressed:
4156
4157	-> gunzip /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux.gz
4158	-> tools/mkimage -n '2.4.4 kernel for TQM850L' \
4159	> -A ppc -O linux -T kernel -C none -a 0 -e 0 \
4160	> -d /opt/elsk/ppc_8xx/usr/src/linux-2.4.4/arch/powerpc/coffboot/vmlinux \
4161	> examples/uImage.TQM850L-uncompressed
4162	Image Name:   2.4.4 kernel for TQM850L
4163	Created:      Wed Jul 19 02:34:59 2000
4164	Image Type:   PowerPC Linux Kernel Image (uncompressed)
4165	Data Size:    792160 Bytes = 773.59 kB = 0.76 MB
4166	Load Address: 0x00000000
4167	Entry Point:  0x00000000
4168
4169
4170Similar you can build U-Boot images from a 'ramdisk.image.gz' file
4171when your kernel is intended to use an initial ramdisk:
4172
4173	-> tools/mkimage -n 'Simple Ramdisk Image' \
4174	> -A ppc -O linux -T ramdisk -C gzip \
4175	> -d /LinuxPPC/images/SIMPLE-ramdisk.image.gz examples/simple-initrd
4176	Image Name:   Simple Ramdisk Image
4177	Created:      Wed Jan 12 14:01:50 2000
4178	Image Type:   PowerPC Linux RAMDisk Image (gzip compressed)
4179	Data Size:    566530 Bytes = 553.25 kB = 0.54 MB
4180	Load Address: 0x00000000
4181	Entry Point:  0x00000000
4182
4183The "dumpimage" is a tool to disassemble images built by mkimage. Its "-i"
4184option performs the converse operation of the mkimage's second form (the "-d"
4185option). Given an image built by mkimage, the dumpimage extracts a "data file"
4186from the image:
4187
4188	tools/dumpimage -i image -T type -p position data_file
4189	  -i ==> extract from the 'image' a specific 'data_file'
4190	  -T ==> set image type to 'type'
4191	  -p ==> 'position' (starting at 0) of the 'data_file' inside the 'image'
4192
4193
4194Installing a Linux Image:
4195-------------------------
4196
4197To downloading a U-Boot image over the serial (console) interface,
4198you must convert the image to S-Record format:
4199
4200	objcopy -I binary -O srec examples/image examples/image.srec
4201
4202The 'objcopy' does not understand the information in the U-Boot
4203image header, so the resulting S-Record file will be relative to
4204address 0x00000000. To load it to a given address, you need to
4205specify the target address as 'offset' parameter with the 'loads'
4206command.
4207
4208Example: install the image to address 0x40100000 (which on the
4209TQM8xxL is in the first Flash bank):
4210
4211	=> erase 40100000 401FFFFF
4212
4213	.......... done
4214	Erased 8 sectors
4215
4216	=> loads 40100000
4217	## Ready for S-Record download ...
4218	~>examples/image.srec
4219	1 2 3 4 5 6 7 8 9 10 11 12 13 ...
4220	...
4221	15989 15990 15991 15992
4222	[file transfer complete]
4223	[connected]
4224	## Start Addr = 0x00000000
4225
4226
4227You can check the success of the download using the 'iminfo' command;
4228this includes a checksum verification so you can be sure no data
4229corruption happened:
4230
4231	=> imi 40100000
4232
4233	## Checking Image at 40100000 ...
4234	   Image Name:	 2.2.13 for initrd on TQM850L
4235	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4236	   Data Size:	 335725 Bytes = 327 kB = 0 MB
4237	   Load Address: 00000000
4238	   Entry Point:	 0000000c
4239	   Verifying Checksum ... OK
4240
4241
4242Boot Linux:
4243-----------
4244
4245The "bootm" command is used to boot an application that is stored in
4246memory (RAM or Flash). In case of a Linux kernel image, the contents
4247of the "bootargs" environment variable is passed to the kernel as
4248parameters. You can check and modify this variable using the
4249"printenv" and "setenv" commands:
4250
4251
4252	=> printenv bootargs
4253	bootargs=root=/dev/ram
4254
4255	=> setenv bootargs root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
4256
4257	=> printenv bootargs
4258	bootargs=root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
4259
4260	=> bootm 40020000
4261	## Booting Linux kernel at 40020000 ...
4262	   Image Name:	 2.2.13 for NFS on TQM850L
4263	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4264	   Data Size:	 381681 Bytes = 372 kB = 0 MB
4265	   Load Address: 00000000
4266	   Entry Point:	 0000000c
4267	   Verifying Checksum ... OK
4268	   Uncompressing Kernel Image ... OK
4269	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
4270	Boot arguments: root=/dev/nfs rw nfsroot=10.0.0.2:/LinuxPPC nfsaddrs=10.0.0.99:10.0.0.2
4271	time_init: decrementer frequency = 187500000/60
4272	Calibrating delay loop... 49.77 BogoMIPS
4273	Memory: 15208k available (700k kernel code, 444k data, 32k init) [c0000000,c1000000]
4274	...
4275
4276If you want to boot a Linux kernel with initial RAM disk, you pass
4277the memory addresses of both the kernel and the initrd image (PPBCOOT
4278format!) to the "bootm" command:
4279
4280	=> imi 40100000 40200000
4281
4282	## Checking Image at 40100000 ...
4283	   Image Name:	 2.2.13 for initrd on TQM850L
4284	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4285	   Data Size:	 335725 Bytes = 327 kB = 0 MB
4286	   Load Address: 00000000
4287	   Entry Point:	 0000000c
4288	   Verifying Checksum ... OK
4289
4290	## Checking Image at 40200000 ...
4291	   Image Name:	 Simple Ramdisk Image
4292	   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
4293	   Data Size:	 566530 Bytes = 553 kB = 0 MB
4294	   Load Address: 00000000
4295	   Entry Point:	 00000000
4296	   Verifying Checksum ... OK
4297
4298	=> bootm 40100000 40200000
4299	## Booting Linux kernel at 40100000 ...
4300	   Image Name:	 2.2.13 for initrd on TQM850L
4301	   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4302	   Data Size:	 335725 Bytes = 327 kB = 0 MB
4303	   Load Address: 00000000
4304	   Entry Point:	 0000000c
4305	   Verifying Checksum ... OK
4306	   Uncompressing Kernel Image ... OK
4307	## Loading RAMDisk Image at 40200000 ...
4308	   Image Name:	 Simple Ramdisk Image
4309	   Image Type:	 PowerPC Linux RAMDisk Image (gzip compressed)
4310	   Data Size:	 566530 Bytes = 553 kB = 0 MB
4311	   Load Address: 00000000
4312	   Entry Point:	 00000000
4313	   Verifying Checksum ... OK
4314	   Loading Ramdisk ... OK
4315	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
4316	Boot arguments: root=/dev/ram
4317	time_init: decrementer frequency = 187500000/60
4318	Calibrating delay loop... 49.77 BogoMIPS
4319	...
4320	RAMDISK: Compressed image found at block 0
4321	VFS: Mounted root (ext2 filesystem).
4322
4323	bash#
4324
4325Boot Linux and pass a flat device tree:
4326-----------
4327
4328First, U-Boot must be compiled with the appropriate defines. See the section
4329titled "Linux Kernel Interface" above for a more in depth explanation. The
4330following is an example of how to start a kernel and pass an updated
4331flat device tree:
4332
4333=> print oftaddr
4334oftaddr=0x300000
4335=> print oft
4336oft=oftrees/mpc8540ads.dtb
4337=> tftp $oftaddr $oft
4338Speed: 1000, full duplex
4339Using TSEC0 device
4340TFTP from server 192.168.1.1; our IP address is 192.168.1.101
4341Filename 'oftrees/mpc8540ads.dtb'.
4342Load address: 0x300000
4343Loading: #
4344done
4345Bytes transferred = 4106 (100a hex)
4346=> tftp $loadaddr $bootfile
4347Speed: 1000, full duplex
4348Using TSEC0 device
4349TFTP from server 192.168.1.1; our IP address is 192.168.1.2
4350Filename 'uImage'.
4351Load address: 0x200000
4352Loading:############
4353done
4354Bytes transferred = 1029407 (fb51f hex)
4355=> print loadaddr
4356loadaddr=200000
4357=> print oftaddr
4358oftaddr=0x300000
4359=> bootm $loadaddr - $oftaddr
4360## Booting image at 00200000 ...
4361   Image Name:	 Linux-2.6.17-dirty
4362   Image Type:	 PowerPC Linux Kernel Image (gzip compressed)
4363   Data Size:	 1029343 Bytes = 1005.2 kB
4364   Load Address: 00000000
4365   Entry Point:	 00000000
4366   Verifying Checksum ... OK
4367   Uncompressing Kernel Image ... OK
4368Booting using flat device tree at 0x300000
4369Using MPC85xx ADS machine description
4370Memory CAM mapping: CAM0=256Mb, CAM1=256Mb, CAM2=0Mb residual: 0Mb
4371[snip]
4372
4373
4374More About U-Boot Image Types:
4375------------------------------
4376
4377U-Boot supports the following image types:
4378
4379   "Standalone Programs" are directly runnable in the environment
4380	provided by U-Boot; it is expected that (if they behave
4381	well) you can continue to work in U-Boot after return from
4382	the Standalone Program.
4383   "OS Kernel Images" are usually images of some Embedded OS which
4384	will take over control completely. Usually these programs
4385	will install their own set of exception handlers, device
4386	drivers, set up the MMU, etc. - this means, that you cannot
4387	expect to re-enter U-Boot except by resetting the CPU.
4388   "RAMDisk Images" are more or less just data blocks, and their
4389	parameters (address, size) are passed to an OS kernel that is
4390	being started.
4391   "Multi-File Images" contain several images, typically an OS
4392	(Linux) kernel image and one or more data images like
4393	RAMDisks. This construct is useful for instance when you want
4394	to boot over the network using BOOTP etc., where the boot
4395	server provides just a single image file, but you want to get
4396	for instance an OS kernel and a RAMDisk image.
4397
4398	"Multi-File Images" start with a list of image sizes, each
4399	image size (in bytes) specified by an "uint32_t" in network
4400	byte order. This list is terminated by an "(uint32_t)0".
4401	Immediately after the terminating 0 follow the images, one by
4402	one, all aligned on "uint32_t" boundaries (size rounded up to
4403	a multiple of 4 bytes).
4404
4405   "Firmware Images" are binary images containing firmware (like
4406	U-Boot or FPGA images) which usually will be programmed to
4407	flash memory.
4408
4409   "Script files" are command sequences that will be executed by
4410	U-Boot's command interpreter; this feature is especially
4411	useful when you configure U-Boot to use a real shell (hush)
4412	as command interpreter.
4413
4414Booting the Linux zImage:
4415-------------------------
4416
4417On some platforms, it's possible to boot Linux zImage. This is done
4418using the "bootz" command. The syntax of "bootz" command is the same
4419as the syntax of "bootm" command.
4420
4421Note, defining the CONFIG_SUPPORT_RAW_INITRD allows user to supply
4422kernel with raw initrd images. The syntax is slightly different, the
4423address of the initrd must be augmented by it's size, in the following
4424format: "<initrd addres>:<initrd size>".
4425
4426
4427Standalone HOWTO:
4428=================
4429
4430One of the features of U-Boot is that you can dynamically load and
4431run "standalone" applications, which can use some resources of
4432U-Boot like console I/O functions or interrupt services.
4433
4434Two simple examples are included with the sources:
4435
4436"Hello World" Demo:
4437-------------------
4438
4439'examples/hello_world.c' contains a small "Hello World" Demo
4440application; it is automatically compiled when you build U-Boot.
4441It's configured to run at address 0x00040004, so you can play with it
4442like that:
4443
4444	=> loads
4445	## Ready for S-Record download ...
4446	~>examples/hello_world.srec
4447	1 2 3 4 5 6 7 8 9 10 11 ...
4448	[file transfer complete]
4449	[connected]
4450	## Start Addr = 0x00040004
4451
4452	=> go 40004 Hello World! This is a test.
4453	## Starting application at 0x00040004 ...
4454	Hello World
4455	argc = 7
4456	argv[0] = "40004"
4457	argv[1] = "Hello"
4458	argv[2] = "World!"
4459	argv[3] = "This"
4460	argv[4] = "is"
4461	argv[5] = "a"
4462	argv[6] = "test."
4463	argv[7] = "<NULL>"
4464	Hit any key to exit ...
4465
4466	## Application terminated, rc = 0x0
4467
4468Another example, which demonstrates how to register a CPM interrupt
4469handler with the U-Boot code, can be found in 'examples/timer.c'.
4470Here, a CPM timer is set up to generate an interrupt every second.
4471The interrupt service routine is trivial, just printing a '.'
4472character, but this is just a demo program. The application can be
4473controlled by the following keys:
4474
4475	? - print current values og the CPM Timer registers
4476	b - enable interrupts and start timer
4477	e - stop timer and disable interrupts
4478	q - quit application
4479
4480	=> loads
4481	## Ready for S-Record download ...
4482	~>examples/timer.srec
4483	1 2 3 4 5 6 7 8 9 10 11 ...
4484	[file transfer complete]
4485	[connected]
4486	## Start Addr = 0x00040004
4487
4488	=> go 40004
4489	## Starting application at 0x00040004 ...
4490	TIMERS=0xfff00980
4491	Using timer 1
4492	  tgcr @ 0xfff00980, tmr @ 0xfff00990, trr @ 0xfff00994, tcr @ 0xfff00998, tcn @ 0xfff0099c, ter @ 0xfff009b0
4493
4494Hit 'b':
4495	[q, b, e, ?] Set interval 1000000 us
4496	Enabling timer
4497Hit '?':
4498	[q, b, e, ?] ........
4499	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0xef6, ter=0x0
4500Hit '?':
4501	[q, b, e, ?] .
4502	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x2ad4, ter=0x0
4503Hit '?':
4504	[q, b, e, ?] .
4505	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x1efc, ter=0x0
4506Hit '?':
4507	[q, b, e, ?] .
4508	tgcr=0x1, tmr=0xff1c, trr=0x3d09, tcr=0x0, tcn=0x169d, ter=0x0
4509Hit 'e':
4510	[q, b, e, ?] ...Stopping timer
4511Hit 'q':
4512	[q, b, e, ?] ## Application terminated, rc = 0x0
4513
4514
4515Minicom warning:
4516================
4517
4518Over time, many people have reported problems when trying to use the
4519"minicom" terminal emulation program for serial download. I (wd)
4520consider minicom to be broken, and recommend not to use it. Under
4521Unix, I recommend to use C-Kermit for general purpose use (and
4522especially for kermit binary protocol download ("loadb" command), and
4523use "cu" for S-Record download ("loads" command).  See
4524http://www.denx.de/wiki/view/DULG/SystemSetup#Section_4.3.
4525for help with kermit.
4526
4527
4528Nevertheless, if you absolutely want to use it try adding this
4529configuration to your "File transfer protocols" section:
4530
4531	   Name	   Program			Name U/D FullScr IO-Red. Multi
4532	X  kermit  /usr/bin/kermit -i -l %l -s	 Y    U	   Y	   N	  N
4533	Y  kermit  /usr/bin/kermit -i -l %l -r	 N    D	   Y	   N	  N
4534
4535
4536NetBSD Notes:
4537=============
4538
4539Starting at version 0.9.2, U-Boot supports NetBSD both as host
4540(build U-Boot) and target system (boots NetBSD/mpc8xx).
4541
4542Building requires a cross environment; it is known to work on
4543NetBSD/i386 with the cross-powerpc-netbsd-1.3 package (you will also
4544need gmake since the Makefiles are not compatible with BSD make).
4545Note that the cross-powerpc package does not install include files;
4546attempting to build U-Boot will fail because <machine/ansi.h> is
4547missing.  This file has to be installed and patched manually:
4548
4549	# cd /usr/pkg/cross/powerpc-netbsd/include
4550	# mkdir powerpc
4551	# ln -s powerpc machine
4552	# cp /usr/src/sys/arch/powerpc/include/ansi.h powerpc/ansi.h
4553	# ${EDIT} powerpc/ansi.h	## must remove __va_list, _BSD_VA_LIST
4554
4555Native builds *don't* work due to incompatibilities between native
4556and U-Boot include files.
4557
4558Booting assumes that (the first part of) the image booted is a
4559stage-2 loader which in turn loads and then invokes the kernel
4560proper. Loader sources will eventually appear in the NetBSD source
4561tree (probably in sys/arc/mpc8xx/stand/u-boot_stage2/); in the
4562meantime, see ftp://ftp.denx.de/pub/u-boot/ppcboot_stage2.tar.gz
4563
4564
4565Implementation Internals:
4566=========================
4567
4568The following is not intended to be a complete description of every
4569implementation detail. However, it should help to understand the
4570inner workings of U-Boot and make it easier to port it to custom
4571hardware.
4572
4573
4574Initial Stack, Global Data:
4575---------------------------
4576
4577The implementation of U-Boot is complicated by the fact that U-Boot
4578starts running out of ROM (flash memory), usually without access to
4579system RAM (because the memory controller is not initialized yet).
4580This means that we don't have writable Data or BSS segments, and BSS
4581is not initialized as zero. To be able to get a C environment working
4582at all, we have to allocate at least a minimal stack. Implementation
4583options for this are defined and restricted by the CPU used: Some CPU
4584models provide on-chip memory (like the IMMR area on MPC8xx and
4585MPC826x processors), on others (parts of) the data cache can be
4586locked as (mis-) used as memory, etc.
4587
4588	Chris Hallinan posted a good summary of these issues to the
4589	U-Boot mailing list:
4590
4591	Subject: RE: [U-Boot-Users] RE: More On Memory Bank x (nothingness)?
4592	From: "Chris Hallinan" <clh@net1plus.com>
4593	Date: Mon, 10 Feb 2003 16:43:46 -0500 (22:43 MET)
4594	...
4595
4596	Correct me if I'm wrong, folks, but the way I understand it
4597	is this: Using DCACHE as initial RAM for Stack, etc, does not
4598	require any physical RAM backing up the cache. The cleverness
4599	is that the cache is being used as a temporary supply of
4600	necessary storage before the SDRAM controller is setup. It's
4601	beyond the scope of this list to explain the details, but you
4602	can see how this works by studying the cache architecture and
4603	operation in the architecture and processor-specific manuals.
4604
4605	OCM is On Chip Memory, which I believe the 405GP has 4K. It
4606	is another option for the system designer to use as an
4607	initial stack/RAM area prior to SDRAM being available. Either
4608	option should work for you. Using CS 4 should be fine if your
4609	board designers haven't used it for something that would
4610	cause you grief during the initial boot! It is frequently not
4611	used.
4612
4613	CONFIG_SYS_INIT_RAM_ADDR should be somewhere that won't interfere
4614	with your processor/board/system design. The default value
4615	you will find in any recent u-boot distribution in
4616	walnut.h should work for you. I'd set it to a value larger
4617	than your SDRAM module. If you have a 64MB SDRAM module, set
4618	it above 400_0000. Just make sure your board has no resources
4619	that are supposed to respond to that address! That code in
4620	start.S has been around a while and should work as is when
4621	you get the config right.
4622
4623	-Chris Hallinan
4624	DS4.COM, Inc.
4625
4626It is essential to remember this, since it has some impact on the C
4627code for the initialization procedures:
4628
4629* Initialized global data (data segment) is read-only. Do not attempt
4630  to write it.
4631
4632* Do not use any uninitialized global data (or implicitly initialized
4633  as zero data - BSS segment) at all - this is undefined, initiali-
4634  zation is performed later (when relocating to RAM).
4635
4636* Stack space is very limited. Avoid big data buffers or things like
4637  that.
4638
4639Having only the stack as writable memory limits means we cannot use
4640normal global data to share information between the code. But it
4641turned out that the implementation of U-Boot can be greatly
4642simplified by making a global data structure (gd_t) available to all
4643functions. We could pass a pointer to this data as argument to _all_
4644functions, but this would bloat the code. Instead we use a feature of
4645the GCC compiler (Global Register Variables) to share the data: we
4646place a pointer (gd) to the global data into a register which we
4647reserve for this purpose.
4648
4649When choosing a register for such a purpose we are restricted by the
4650relevant  (E)ABI  specifications for the current architecture, and by
4651GCC's implementation.
4652
4653For PowerPC, the following registers have specific use:
4654	R1:	stack pointer
4655	R2:	reserved for system use
4656	R3-R4:	parameter passing and return values
4657	R5-R10: parameter passing
4658	R13:	small data area pointer
4659	R30:	GOT pointer
4660	R31:	frame pointer
4661
4662	(U-Boot also uses R12 as internal GOT pointer. r12
4663	is a volatile register so r12 needs to be reset when
4664	going back and forth between asm and C)
4665
4666    ==> U-Boot will use R2 to hold a pointer to the global data
4667
4668    Note: on PPC, we could use a static initializer (since the
4669    address of the global data structure is known at compile time),
4670    but it turned out that reserving a register results in somewhat
4671    smaller code - although the code savings are not that big (on
4672    average for all boards 752 bytes for the whole U-Boot image,
4673    624 text + 127 data).
4674
4675On ARM, the following registers are used:
4676
4677	R0:	function argument word/integer result
4678	R1-R3:	function argument word
4679	R9:	platform specific
4680	R10:	stack limit (used only if stack checking is enabled)
4681	R11:	argument (frame) pointer
4682	R12:	temporary workspace
4683	R13:	stack pointer
4684	R14:	link register
4685	R15:	program counter
4686
4687    ==> U-Boot will use R9 to hold a pointer to the global data
4688
4689    Note: on ARM, only R_ARM_RELATIVE relocations are supported.
4690
4691On Nios II, the ABI is documented here:
4692	http://www.altera.com/literature/hb/nios2/n2cpu_nii51016.pdf
4693
4694    ==> U-Boot will use gp to hold a pointer to the global data
4695
4696    Note: on Nios II, we give "-G0" option to gcc and don't use gp
4697    to access small data sections, so gp is free.
4698
4699On NDS32, the following registers are used:
4700
4701	R0-R1:	argument/return
4702	R2-R5:	argument
4703	R15:	temporary register for assembler
4704	R16:	trampoline register
4705	R28:	frame pointer (FP)
4706	R29:	global pointer (GP)
4707	R30:	link register (LP)
4708	R31:	stack pointer (SP)
4709	PC:	program counter (PC)
4710
4711    ==> U-Boot will use R10 to hold a pointer to the global data
4712
4713NOTE: DECLARE_GLOBAL_DATA_PTR must be used with file-global scope,
4714or current versions of GCC may "optimize" the code too much.
4715
4716On RISC-V, the following registers are used:
4717
4718	x0: hard-wired zero (zero)
4719	x1: return address (ra)
4720	x2:	stack pointer (sp)
4721	x3:	global pointer (gp)
4722	x4:	thread pointer (tp)
4723	x5:	link register (t0)
4724	x8:	frame pointer (fp)
4725	x10-x11:	arguments/return values (a0-1)
4726	x12-x17:	arguments (a2-7)
4727	x28-31:	 temporaries (t3-6)
4728	pc:	program counter (pc)
4729
4730    ==> U-Boot will use gp to hold a pointer to the global data
4731
4732Memory Management:
4733------------------
4734
4735U-Boot runs in system state and uses physical addresses, i.e. the
4736MMU is not used either for address mapping nor for memory protection.
4737
4738The available memory is mapped to fixed addresses using the memory
4739controller. In this process, a contiguous block is formed for each
4740memory type (Flash, SDRAM, SRAM), even when it consists of several
4741physical memory banks.
4742
4743U-Boot is installed in the first 128 kB of the first Flash bank (on
4744TQM8xxL modules this is the range 0x40000000 ... 0x4001FFFF). After
4745booting and sizing and initializing DRAM, the code relocates itself
4746to the upper end of DRAM. Immediately below the U-Boot code some
4747memory is reserved for use by malloc() [see CONFIG_SYS_MALLOC_LEN
4748configuration setting]. Below that, a structure with global Board
4749Info data is placed, followed by the stack (growing downward).
4750
4751Additionally, some exception handler code is copied to the low 8 kB
4752of DRAM (0x00000000 ... 0x00001FFF).
4753
4754So a typical memory configuration with 16 MB of DRAM could look like
4755this:
4756
4757	0x0000 0000	Exception Vector code
4758	      :
4759	0x0000 1FFF
4760	0x0000 2000	Free for Application Use
4761	      :
4762	      :
4763
4764	      :
4765	      :
4766	0x00FB FF20	Monitor Stack (Growing downward)
4767	0x00FB FFAC	Board Info Data and permanent copy of global data
4768	0x00FC 0000	Malloc Arena
4769	      :
4770	0x00FD FFFF
4771	0x00FE 0000	RAM Copy of Monitor Code
4772	...		eventually: LCD or video framebuffer
4773	...		eventually: pRAM (Protected RAM - unchanged by reset)
4774	0x00FF FFFF	[End of RAM]
4775
4776
4777System Initialization:
4778----------------------
4779
4780In the reset configuration, U-Boot starts at the reset entry point
4781(on most PowerPC systems at address 0x00000100). Because of the reset
4782configuration for CS0# this is a mirror of the on board Flash memory.
4783To be able to re-map memory U-Boot then jumps to its link address.
4784To be able to implement the initialization code in C, a (small!)
4785initial stack is set up in the internal Dual Ported RAM (in case CPUs
4786which provide such a feature like), or in a locked part of the data
4787cache. After that, U-Boot initializes the CPU core, the caches and
4788the SIU.
4789
4790Next, all (potentially) available memory banks are mapped using a
4791preliminary mapping. For example, we put them on 512 MB boundaries
4792(multiples of 0x20000000: SDRAM on 0x00000000 and 0x20000000, Flash
4793on 0x40000000 and 0x60000000, SRAM on 0x80000000). Then UPM A is
4794programmed for SDRAM access. Using the temporary configuration, a
4795simple memory test is run that determines the size of the SDRAM
4796banks.
4797
4798When there is more than one SDRAM bank, and the banks are of
4799different size, the largest is mapped first. For equal size, the first
4800bank (CS2#) is mapped first. The first mapping is always for address
48010x00000000, with any additional banks following immediately to create
4802contiguous memory starting from 0.
4803
4804Then, the monitor installs itself at the upper end of the SDRAM area
4805and allocates memory for use by malloc() and for the global Board
4806Info data; also, the exception vector code is copied to the low RAM
4807pages, and the final stack is set up.
4808
4809Only after this relocation will you have a "normal" C environment;
4810until that you are restricted in several ways, mostly because you are
4811running from ROM, and because the code will have to be relocated to a
4812new address in RAM.
4813
4814
4815U-Boot Porting Guide:
4816----------------------
4817
4818[Based on messages by Jerry Van Baren in the U-Boot-Users mailing
4819list, October 2002]
4820
4821
4822int main(int argc, char *argv[])
4823{
4824	sighandler_t no_more_time;
4825
4826	signal(SIGALRM, no_more_time);
4827	alarm(PROJECT_DEADLINE - toSec (3 * WEEK));
4828
4829	if (available_money > available_manpower) {
4830		Pay consultant to port U-Boot;
4831		return 0;
4832	}
4833
4834	Download latest U-Boot source;
4835
4836	Subscribe to u-boot mailing list;
4837
4838	if (clueless)
4839		email("Hi, I am new to U-Boot, how do I get started?");
4840
4841	while (learning) {
4842		Read the README file in the top level directory;
4843		Read http://www.denx.de/twiki/bin/view/DULG/Manual;
4844		Read applicable doc/*.README;
4845		Read the source, Luke;
4846		/* find . -name "*.[chS]" | xargs grep -i <keyword> */
4847	}
4848
4849	if (available_money > toLocalCurrency ($2500))
4850		Buy a BDI3000;
4851	else
4852		Add a lot of aggravation and time;
4853
4854	if (a similar board exists) {	/* hopefully... */
4855		cp -a board/<similar> board/<myboard>
4856		cp include/configs/<similar>.h include/configs/<myboard>.h
4857	} else {
4858		Create your own board support subdirectory;
4859		Create your own board include/configs/<myboard>.h file;
4860	}
4861	Edit new board/<myboard> files
4862	Edit new include/configs/<myboard>.h
4863
4864	while (!accepted) {
4865		while (!running) {
4866			do {
4867				Add / modify source code;
4868			} until (compiles);
4869			Debug;
4870			if (clueless)
4871				email("Hi, I am having problems...");
4872		}
4873		Send patch file to the U-Boot email list;
4874		if (reasonable critiques)
4875			Incorporate improvements from email list code review;
4876		else
4877			Defend code as written;
4878	}
4879
4880	return 0;
4881}
4882
4883void no_more_time (int sig)
4884{
4885      hire_a_guru();
4886}
4887
4888
4889Coding Standards:
4890-----------------
4891
4892All contributions to U-Boot should conform to the Linux kernel
4893coding style; see the kernel coding style guide at
4894https://www.kernel.org/doc/html/latest/process/coding-style.html, and the
4895script "scripts/Lindent" in your Linux kernel source directory.
4896
4897Source files originating from a different project (for example the
4898MTD subsystem) are generally exempt from these guidelines and are not
4899reformatted to ease subsequent migration to newer versions of those
4900sources.
4901
4902Please note that U-Boot is implemented in C (and to some small parts in
4903Assembler); no C++ is used, so please do not use C++ style comments (//)
4904in your code.
4905
4906Please also stick to the following formatting rules:
4907- remove any trailing white space
4908- use TAB characters for indentation and vertical alignment, not spaces
4909- make sure NOT to use DOS '\r\n' line feeds
4910- do not add more than 2 consecutive empty lines to source files
4911- do not add trailing empty lines to source files
4912
4913Submissions which do not conform to the standards may be returned
4914with a request to reformat the changes.
4915
4916
4917Submitting Patches:
4918-------------------
4919
4920Since the number of patches for U-Boot is growing, we need to
4921establish some rules. Submissions which do not conform to these rules
4922may be rejected, even when they contain important and valuable stuff.
4923
4924Please see http://www.denx.de/wiki/U-Boot/Patches for details.
4925
4926Patches shall be sent to the u-boot mailing list <u-boot@lists.denx.de>;
4927see https://lists.denx.de/listinfo/u-boot
4928
4929When you send a patch, please include the following information with
4930it:
4931
4932* For bug fixes: a description of the bug and how your patch fixes
4933  this bug. Please try to include a way of demonstrating that the
4934  patch actually fixes something.
4935
4936* For new features: a description of the feature and your
4937  implementation.
4938
4939* A CHANGELOG entry as plaintext (separate from the patch)
4940
4941* For major contributions, add a MAINTAINERS file with your
4942  information and associated file and directory references.
4943
4944* When you add support for a new board, don't forget to add a
4945  maintainer e-mail address to the boards.cfg file, too.
4946
4947* If your patch adds new configuration options, don't forget to
4948  document these in the README file.
4949
4950* The patch itself. If you are using git (which is *strongly*
4951  recommended) you can easily generate the patch using the
4952  "git format-patch". If you then use "git send-email" to send it to
4953  the U-Boot mailing list, you will avoid most of the common problems
4954  with some other mail clients.
4955
4956  If you cannot use git, use "diff -purN OLD NEW". If your version of
4957  diff does not support these options, then get the latest version of
4958  GNU diff.
4959
4960  The current directory when running this command shall be the parent
4961  directory of the U-Boot source tree (i. e. please make sure that
4962  your patch includes sufficient directory information for the
4963  affected files).
4964
4965  We prefer patches as plain text. MIME attachments are discouraged,
4966  and compressed attachments must not be used.
4967
4968* If one logical set of modifications affects or creates several
4969  files, all these changes shall be submitted in a SINGLE patch file.
4970
4971* Changesets that contain different, unrelated modifications shall be
4972  submitted as SEPARATE patches, one patch per changeset.
4973
4974
4975Notes:
4976
4977* Before sending the patch, run the buildman script on your patched
4978  source tree and make sure that no errors or warnings are reported
4979  for any of the boards.
4980
4981* Keep your modifications to the necessary minimum: A patch
4982  containing several unrelated changes or arbitrary reformats will be
4983  returned with a request to re-formatting / split it.
4984
4985* If you modify existing code, make sure that your new code does not
4986  add to the memory footprint of the code ;-) Small is beautiful!
4987  When adding new features, these should compile conditionally only
4988  (using #ifdef), and the resulting code with the new feature
4989  disabled must not need more memory than the old code without your
4990  modification.
4991
4992* Remember that there is a size limit of 100 kB per message on the
4993  u-boot mailing list. Bigger patches will be moderated. If they are
4994  reasonable and not too big, they will be acknowledged. But patches
4995  bigger than the size limit should be avoided.
4996