Commit 6122f0d5 authored by Tim Harvey's avatar Tim Harvey Committed by Stefano Babic
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imx: ventana: update README with Falcon mode documentation


Signed-off-by: default avatarTim Harvey <tharvey@gateworks.com>
parent 40e999ca
......@@ -149,3 +149,172 @@ This information is taken from:
More details about the i.MX6 BOOT ROM can be found in the IMX6 reference manual.
4. Falcon Mode
------------------------------
The Gateworks Ventana board config enables Falcon mode (CONFIG_SPL_OS_BOOT)
which allows the SPL to boot directly to an OS instead of to U-Boot
(u-boot.img) thus acheiving a faster overall boot time. The time savings
depends on your boot medium (ie NAND Flash vs micro-SD) and size/storage
of the OS. The time savings can be anywhere from 2 seconds (256MB NAND Flash
with ~1MB kernel) to 6 seconds or more (2GB NAND Flash with ~6 kernel)
The Gateworks Ventana board supports Falcon mode for the following boot
medium:
- NAND flash
- micro-SD
For all boot mediums, raw mode is used. While support of more complex storage
such as files on top of FAT/EXT filesystem is possible but not practical
as the size of the SPL is fairly limitted (to 64KB based on the smallest
size of available IMX6 iRAM) as well as the fact that this would increase
OS load time which defeats the purpose of Falcon mode in the first place.
The SPL decides to boot either U-Boot (u-boot.img) or the OS (args + kernel)
based on the return value of the spl_start_uboot() function. While often
this can simply be the state of a GPIO based pushbutton or DIP switch, for
Gateworks Ventana, we use the U-Boot environment 'boot_os' variable which if
set to '1' will choose to boot the OS rather than U-Boot. While the choice
of adding env support to the SPL adds a little bit of time to the boot
process as well as (significant really) SPL code space this was deemed most
flexible as within the large variety of Gateworks Ventana boards not all of
them have a user pushbutton and that pushbutton may be configured as a hard
reset per user configuration.
To use Falcon mode it is required that you first 'prepare' the 'args' data
that is stored on your boot medium along with the kernel (which can be any
OS or bare-metal application). In the case of the Linux kernel the 'args'
is the flatenned device-tree which normally gets altered prior to booting linux
by U-Boot's 'bootm' command. To achieve this for SPL we use the
'spl export fdt' command in U-Boot after loading the kernel and dtb which
will go through the same process of modifying the device-tree for the board
being executed on but not jump to the kernel. This allows you to save the
args data to the location the SPL expects it and then enable Falcon mode.
It is important to realize that there are certain values in the dtb that
are board model specific (IMX6Q vs IMX6DL for example) and board specific
(board serial number, MAC addrs) so you do not want to use the 'args'
data prepared from one board on another board.
4.1. Falcon Mode on NAND flash
------------------------------
To prepare a Gateworks Ventana board that boots from NAND flash for Falcon
mode you must program your flash such that the 'args' and 'kernel' are
located where defined at compile time by the following:
CONFIG_CMD_SPL_NAND_OFS 17MB - offset of 'args'
CONFIG_SYS_NAND_SPL_KERNEL_OFFS 18MB - offset of 'kernel'
The location offsets defined above are defaults chosen by Gateworks and are
flexible if you want to re-define them.
The following steps executed in U-Boot will configure Falcon mode for NAND
using rootfs (ubi), kernel (uImage), and dtb from the network:
# change mtd partitions to the above mapping
Ventana > setenv mtdparts 'mtdparts=nand:14m(spl),2m(uboot),1m(env),1m(args),10m(kernel),-(rootfs)'
# flash rootfs (at 28MB)
Ventana > tftp ${loadaddr} rootfs_${flash_layout}.ubi && \
nand erase.part rootfs && nand write ${loadaddr} rootfs ${filesize}
# load the device-tree
Ventana > tftp ${fdt_addr} ventana/${fdt_file2}
# load the kernel
Ventana > tftp ${loadaddr} ventana/uImage
# flash kernel (at 18MB)
Ventana > nand erase.part kernel && nand write ${loadaddr} kernel ${filesize}
# set kernel args for the console and rootfs (used by spl export)
Ventana > setenv bootargs 'console=ttymxc1,115200 root=ubi0:rootfs ubi.mtd=5 rootfstype=ubifs quiet'
# create args based on env, board, EEPROM, and dtb
Ventana > spl export fdt ${loadaddr} - ${fdt_addr}
# flash args (at 17MB)
Ventana > nand erase.part args && nand write 18000000 args 100000
# set boot_os env var to enable booting to Linux
Ventana > setenv boot_os 1 && saveenv
Be sure to adjust 'bootargs' above to your OS needs (this will be different
for various distros such as OpenWrt, Yocto, Android, etc). You can use the
value obtained from 'cat /proc/cmdline' when booted to Linux.
This information is taken from:
http://trac.gateworks.com/wiki/ventana/bootloader/falcon-mode#nand
4.2. Falcon Mode on micro-SD card
---------------------------------
To prepare a Gateworks Ventana board with a primary boot device of micro-SD
you first need to make sure you build U-Boot with CONFIG_ENV_IS_IN_MMC
instead of CONFIG_ENV_IS_IN_NAND.
For micro-SD based Falcon mode you must program your micro-SD such that
the 'args' and 'kernel' are located where defined at compile time
by the following:
CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR 0x800 (1MB) - offset of 'args'
CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR 0x1000 (2MB) - offset of 'kernel'
The location offsets defined above are defaults chosen by Gateworks and are
flexible if you want to re-define them.
First you must prepare a micro-SD such that the SPL can be loaded by the
IMX6 BOOT ROM (fixed offset of 1KB), and U-Boot can be loaded by the SPL
(fixed offset of 69KB defined by CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR).
The following shell commands are executed on a Linux host (adjust DEV to the
block storage device of your micro-SD):
DEV=/dev/sdc
# zero out 1MB of device
sudo dd if=/dev/zero of=$DEV count=1 bs=1M oflag=sync status=none && sync
# copy SPL to 1KB offset
sudo dd if=SPL of=$DEV bs=1K seek=1 oflag=sync status=none && sync
# copy U-Boot to 69KB offset
sudo dd if=u-boot.img of=$DEV bs=1K seek=69 oflag=sync status=none && sync
# create a partition table with a single rootfs partition starting at 10MB
printf "10,,L\n" | sudo sfdisk --in-order --no-reread -L -uM $DEV && sync
# format partition
sudo mkfs.ext4 -L root ${DEV}1
# mount the partition
sudo udisks --mount ${DEV}1
# extract filesystem
sudo tar xvf rootfs.tar.gz -C /media/root
# flush and unmount
sync && sudo umount /media/root
Now that your micro-SD partitioning has been adjusted to leave room for the
raw 'args' and 'kernel' data boot the board with the prepared micro-SD, break
out in U-Boot and use the following to enable Falcon mode:
# load device-tree from rootfs
Ventana > ext2load mmc 0:1 ${fdt_addr} boot/${fdt_file2}
# load kernel from rootfs
Ventana > ext2load mmc 0:1 ${loadaddr} boot/uImage
# write kernel at 2MB offset
Ventana > mmc write ${loadaddr} 0x1000 0x4000
# setup kernel bootargs
Ventana > setenv bootargs 'console=ttymxc1,115200 root=/dev/mmcblk0p1 rootfstype=ext4 rootwait rw'
# prepare args
Ventana > spl export fdt ${loadaddr} - ${fdt_addr}
# write args 1MB data (0x800 sectors) to 1MB offset (0x800 sectors)
Ventana > mmc write 18000000 0x800 0x800
# set boot_os to enable falcon mode
Ventana > setenv boot_os 1 && saveenv
Be sure to adjust 'bootargs' above to your OS needs (this will be different
for various distros such as OpenWrt, Yocto, Android, etc). You can use the
value obtained from 'cat /proc/cmdline' when booted to Linux.
This information is taken from:
http://trac.gateworks.com/wiki/ventana/bootloader/falcon-mode#microsd
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