1U-Boot for the Gateworks Ventana Product Family boards
2
3This file contains information for the port of U-Boot to the Gateworks
4Ventana Product family boards.
5
6The entire Ventana product family (http://www.gateworks.com/product#ventana)
7is supported by a single bootloader build by using a common SPL and U-Boot
8that dynamically determines the characterstics of the board at runtime via
9information from an EEPROM on the board programmed at the factory and supports
10all of the various boot mediums available.
11
121. Secondary Program Loader (SPL)
13---------------------------------
14
15The i.MX6 has a BOOT ROM PPL (Primary Program Loader) which supports loading
16an executable image from various boot devices.
17
18The Gateworks Ventana board config uses an SPL build configuration. This
19will build the following artifacts from u-boot source:
20 - SPL - Secondary Program Loader that the i.MX6 BOOT ROM (Primary Program
21         Loader) boots.  This detects CPU/DRAM configuration, configures
22         The DRAM controller, loads u-boot.img from the detected boot device,
23         and jumps to it.  As this is booted from the PPL, it has an IVT/DCD
24         table.
25 - u-boot.img - The main u-boot core which is u-boot.bin with a image header.
26
27
282. Build
29--------
30
31To build U-Boot for the Gateworks Ventana product family:
32
33 make gwventana_config
34 make
35
36
373. Boot source:
38---------------
39
40The Gateworks Ventana boards support booting from NAND or micro-SD depending
41on the board model. The IMX6 BOOT ROM will choose a boot media based on eFUSE
42settings programmed at the factory.
43
44Boards with NAND flash will always boot from NAND, and NAND-less boards will
45always boot from micro-SD. However, it is possible to use the U-Boot bmode
46command (or the technique it uses) to essentially bootstrap to another boot
47media at runtime.
48
493.1. boot from NAND
50-------------------
51
52The i.MX6 BOOT ROM expects some structures that provide details of NAND layout
53and bad block information (referred to as 'bootstreams') which are replicated
54multiple times in NAND. The number of replications and their spacing (referred
55to as search stride) is configurable through board strapping options and/or
56eFUSE settings (BOOT_SEARCH_COUNT / Pages in block from BOOT_CFG2). In
57addition, the i.MX6 BOOT ROM Flash Configuration Block (FCB) supports two
58copies of a bootloader in flash in the case that a bad block has corrupted one.
59The Freescale 'kobs-ng' application from the Freescale LTIB BSP, which runs
60under Linux and operates on an MTD partition, must be used to program the
61bootstream in order to setup this flash structure correctly.
62
63The Gateworks Ventana boards with NAND flash have been factory programmed
64such that their eFUSE settings expect 2 copies of the boostream (this is
65specified by providing kobs-ng with the --search_exponent=1 argument). Once in
66Linux with MTD support for the NAND on /dev/mtd0 you can program the SPL
67with:
68
69kobs-ng init -v -x --search_exponent=1 SPL
70
71The kobs-ng application uses an imximage which contains the Image Vector Table
72(IVT) and Device Configuration Data (DCD) structures that the i.MX6 BOOT ROM
73requires to boot.  The kobs-ng adds the Firmware Configuration Block (FCB) and
74Discovered Bad Block Table (DBBT).  The SPL build artifact from u-boot is
75an imximage.
76
77The u-boot.img, which is the non SPL u-boot binary appended to a u-boot image
78header must be programmed in the NAND flash boot device at an offset hard
79coded in the SPL. For the Ventana boards, this has been chosen to be 14MB.
80The image can be programmed from either u-boot or Linux:
81
82u-boot:
83Ventana > setenv mtdparts mtdparts=nand:14m(spl),2m(uboot),1m(env),-(rootfs)
84Ventana > tftp ${loadaddr} u-boot.img && nand erase.part uboot && \
85          nand write ${loadaddr} uboot ${filesize}
86
87Linux:
88nandwrite /dev/mtd1 u-boot.img
89
90The above assumes the default Ventana partitioning scheme which is configured
91via the mtdparts env var:
92 - spl: 14MB
93 - uboot: 2M
94 - env: 1M
95 - rootfs: the rest
96
97This information is taken from:
98  http://trac.gateworks.com/wiki/ventana/bootloader#nand
99
100More details about the i.MX6 BOOT ROM can be found in the IMX6 reference manual.
101
1023.1. boot from micro-SD
103-----------------------
104
105When the IMX6 eFUSE settings have been factory programmed to boot from
106micro-SD the SPL will be loaded from offset 0x400 (1KB). Once the SPL is
107booted, it will load and execute U-boot (u-boot.img) from offset 69KB
108on the micro-SD (defined by CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR).
109
110While it is technically possible to enable the SPL to be able to load
111U-Boot from a file on a FAT/EXT filesystem on the micro-SD, we chose to
112use raw micro-SD access to keep the code-size and boot time of the SPL down.
113
114For these reasons a micro-SD that will be used as an IMX6 primary boot
115device must be carefully partitioned and prepared.
116
117The following shell commands are executed on a Linux host (adjust DEV to the
118block storage device of your micro-SD):
119
120 DEV=/dev/sdc
121 # zero out 1MB of device
122 sudo dd if=/dev/zero of=$DEV count=1 bs=1M oflag=sync status=none && sync
123 # copy SPL to 1KB offset
124 sudo dd if=SPL of=$DEV bs=1K seek=1 oflag=sync status=none && sync
125 # copy U-Boot to 69KB offset
126 sudo dd if=u-boot.img of=$DEV bs=1K seek=69 oflag=sync status=none && sync
127 # create a partition table with a single rootfs partition starting at 1MB
128 printf "1,,L\n" | sudo sfdisk --in-order --no-reread -L -uM $DEV && sync
129 # format partition
130 sudo mkfs.ext4 -L root ${DEV}1
131 # mount the partition
132 sudo udisks --mount ${DEV}1
133 # extract filesystem
134 sudo tar xvf rootfs.tar.gz -C /media/root
135 # flush and unmount
136 sync && sudo umount /media/root
137
138The above assumes the default Ventana micro-SD partitioning scheme
139 - spl    :   1KB-69KB  (68KB)  required by IMX6 BOOT ROM
140 - uboot  :  69KB-709KB (640KB) defined by
141                                CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR
142 - env    : 709KB-965KB (256KB) defined by
143                                CONFIG_ENV_MMC_SIZE
144                                CONFIG_ENV_MMC_OFFSET_REDUND
145 - rootfs :   1MB-
146
147This information is taken from:
148  http://trac.gateworks.com/wiki/ventana/bootloader#microsd
149
150More details about the i.MX6 BOOT ROM can be found in the IMX6 reference manual.
151
1524. Falcon Mode
153------------------------------
154
155The Gateworks Ventana board config enables Falcon mode (CONFIG_SPL_OS_BOOT)
156which allows the SPL to boot directly to an OS instead of to U-Boot
157(u-boot.img) thus acheiving a faster overall boot time. The time savings
158depends on your boot medium (ie NAND Flash vs micro-SD) and size/storage
159of the OS. The time savings can be anywhere from 2 seconds (256MB NAND Flash
160with ~1MB kernel) to 6 seconds or more (2GB NAND Flash with ~6 kernel)
161
162The Gateworks Ventana board supports Falcon mode for the following boot
163medium:
164 - NAND flash
165 - micro-SD
166
167For all boot mediums, raw mode is used. While support of more complex storage
168such as files on top of FAT/EXT filesystem is possible but not practical
169as the size of the SPL is fairly limitted (to 64KB based on the smallest
170size of available IMX6 iRAM) as well as the fact that this would increase
171OS load time which defeats the purpose of Falcon mode in the first place.
172
173The SPL decides to boot either U-Boot (u-boot.img) or the OS (args + kernel)
174based on the return value of the spl_start_uboot() function. While often
175this can simply be the state of a GPIO based pushbutton or DIP switch, for
176Gateworks Ventana, we use the U-Boot environment 'boot_os' variable which if
177set to '1' will choose to boot the OS rather than U-Boot. While the choice
178of adding env support to the SPL adds a little bit of time to the boot
179process as well as (significant really) SPL code space this was deemed most
180flexible as within the large variety of Gateworks Ventana boards not all of
181them have a user pushbutton and that pushbutton may be configured as a hard
182reset per user configuration.
183
184To use Falcon mode it is required that you first 'prepare' the 'args' data
185that is stored on your boot medium along with the kernel (which can be any
186OS or bare-metal application). In the case of the Linux kernel the 'args'
187is the flatenned device-tree which normally gets altered prior to booting linux
188by U-Boot's 'bootm' command. To achieve this for SPL we use the
189'spl export fdt' command in U-Boot after loading the kernel and dtb which
190will go through the same process of modifying the device-tree for the board
191being executed on but not jump to the kernel. This allows you to save the
192args data to the location the SPL expects it and then enable Falcon mode.
193
194It is important to realize that there are certain values in the dtb that
195are board model specific (IMX6Q vs IMX6DL for example) and board specific
196(board serial number, MAC addrs) so you do not want to use the 'args'
197data prepared from one board on another board.
198
1994.1. Falcon Mode on NAND flash
200------------------------------
201To prepare a Gateworks Ventana board that boots from NAND flash for Falcon
202mode you must program your flash such that the 'args' and 'kernel' are
203located where defined at compile time by the following:
204   CONFIG_CMD_SPL_NAND_OFS         17MB - offset of 'args'
205   CONFIG_SYS_NAND_SPL_KERNEL_OFFS 18MB - offset of 'kernel'
206
207The location offsets defined above are defaults chosen by Gateworks and are
208flexible if you want to re-define them.
209
210The following steps executed in U-Boot will configure Falcon mode for NAND
211using rootfs (ubi), kernel (uImage), and dtb from the network:
212
213 # change mtd partitions to the above mapping
214 Ventana > setenv mtdparts 'mtdparts=nand:14m(spl),2m(uboot),1m(env),1m(args),10m(kernel),-(rootfs)'
215
216 # flash rootfs (at 28MB)
217 Ventana > tftp ${loadaddr} rootfs_${flash_layout}.ubi && \
218   nand erase.part rootfs && nand write ${loadaddr} rootfs ${filesize}
219
220 # load the device-tree
221 Ventana > tftp ${fdt_addr} ventana/${fdt_file2}
222
223 # load the kernel
224 Ventana > tftp ${loadaddr} ventana/uImage
225
226 # flash kernel (at 18MB)
227 Ventana > nand erase.part kernel && nand write ${loadaddr} kernel ${filesize}
228
229 # set kernel args for the console and rootfs (used by spl export)
230 Ventana > setenv bootargs 'console=ttymxc1,115200 root=ubi0:rootfs ubi.mtd=5 rootfstype=ubifs quiet'
231
232 # create args based on env, board, EEPROM, and dtb
233 Ventana > spl export fdt ${loadaddr} - ${fdt_addr}
234
235 # flash args (at 17MB)
236 Ventana > nand erase.part args && nand write 18000000 args 100000
237
238 # set boot_os env var to enable booting to Linux
239 Ventana > setenv boot_os 1 && saveenv
240
241Be sure to adjust 'bootargs' above to your OS needs (this will be different
242for various distros such as OpenWrt, Yocto, Android, etc). You can use the
243value obtained from 'cat /proc/cmdline' when booted to Linux.
244
245This information is taken from:
246  http://trac.gateworks.com/wiki/ventana/bootloader/falcon-mode#nand
247
248
2494.2. Falcon Mode on micro-SD card
250---------------------------------
251
252To prepare a Gateworks Ventana board with a primary boot device of micro-SD
253you first need to make sure you build U-Boot with CONFIG_ENV_IS_IN_MMC
254instead of CONFIG_ENV_IS_IN_NAND.
255
256For micro-SD based Falcon mode you must program your micro-SD such that
257the 'args' and 'kernel' are located where defined at compile time
258by the following:
259   CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR 0x800 (1MB) - offset of 'args'
260   CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR 0x1000 (2MB) - offset of 'kernel'
261
262The location offsets defined above are defaults chosen by Gateworks and are
263flexible if you want to re-define them.
264
265First you must prepare a micro-SD such that the SPL can be loaded by the
266IMX6 BOOT ROM (fixed offset of 1KB), and U-Boot can be loaded by the SPL
267(fixed offset of 69KB defined by CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR).
268
269The following shell commands are executed on a Linux host (adjust DEV to the
270block storage device of your micro-SD):
271
272 DEV=/dev/sdc
273 # zero out 1MB of device
274 sudo dd if=/dev/zero of=$DEV count=1 bs=1M oflag=sync status=none && sync
275 # copy SPL to 1KB offset
276 sudo dd if=SPL of=$DEV bs=1K seek=1 oflag=sync status=none && sync
277 # copy U-Boot to 69KB offset
278 sudo dd if=u-boot.img of=$DEV bs=1K seek=69 oflag=sync status=none && sync
279 # create a partition table with a single rootfs partition starting at 10MB
280 printf "10,,L\n" | sudo sfdisk --in-order --no-reread -L -uM $DEV && sync
281 # format partition
282 sudo mkfs.ext4 -L root ${DEV}1
283 # mount the partition
284 sudo udisks --mount ${DEV}1
285 # extract filesystem
286 sudo tar xvf rootfs.tar.gz -C /media/root
287 # flush and unmount
288 sync && sudo umount /media/root
289
290Now that your micro-SD partitioning has been adjusted to leave room for the
291raw 'args' and 'kernel' data boot the board with the prepared micro-SD, break
292out in U-Boot and use the following to enable Falcon mode:
293
294 # load device-tree from rootfs
295 Ventana > ext2load mmc 0:1 ${fdt_addr} boot/${fdt_file2}
296
297 # load kernel from rootfs
298 Ventana > ext2load mmc 0:1 ${loadaddr} boot/uImage
299
300 # write kernel at 2MB offset
301 Ventana > mmc write ${loadaddr} 0x1000 0x4000
302
303 # setup kernel bootargs
304 Ventana > setenv bootargs 'console=ttymxc1,115200 root=/dev/mmcblk0p1 rootfstype=ext4 rootwait rw'
305
306 # prepare args
307 Ventana > spl export fdt ${loadaddr} - ${fdt_addr}
308
309 # write args 1MB data (0x800 sectors) to 1MB offset (0x800 sectors)
310 Ventana > mmc write 18000000 0x800 0x800
311
312 # set boot_os to enable falcon mode
313 Ventana > setenv boot_os 1 && saveenv
314
315Be sure to adjust 'bootargs' above to your OS needs (this will be different
316for various distros such as OpenWrt, Yocto, Android, etc). You can use the
317value obtained from 'cat /proc/cmdline' when booted to Linux.
318
319This information is taken from:
320  http://trac.gateworks.com/wiki/ventana/bootloader/falcon-mode#microsd
321