Signed-off-by: Tim Harvey tharvey@gateworks.com --- board/gateworks/gw_ventana/README | 169 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 169 insertions(+)
diff --git a/board/gateworks/gw_ventana/README b/board/gateworks/gw_ventana/README index 74698b7..697e5c8 100644 --- a/board/gateworks/gw_ventana/README +++ b/board/gateworks/gw_ventana/README @@ -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