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- U-Boot for the Gateworks Ventana Product Family boards
- This file contains information for the port of U-Boot to the Gateworks
- Ventana Product family boards.
- The entire Ventana product family (http://www.gateworks.com/product#ventana)
- is supported by a single bootloader build by using a common SPL and U-Boot
- that dynamically determines the characterstics of the board at runtime via
- information from an EEPROM on the board programmed at the factory and supports
- all of the various boot mediums available.
- 1. Secondary Program Loader (SPL)
- ---------------------------------
- The i.MX6 has a BOOT ROM PPL (Primary Program Loader) which supports loading
- an executable image from various boot devices.
- The Gateworks Ventana board config uses an SPL build configuration. This
- will build the following artifacts from U-Boot source:
- - SPL - Secondary Program Loader that the i.MX6 BOOT ROM (Primary Program
- Loader) boots. This detects CPU/DRAM configuration, configures
- The DRAM controller, loads u-boot.img from the detected boot device,
- and jumps to it. As this is booted from the PPL, it has an IVT/DCD
- table.
- - u-boot.img - The main U-Boot core which is u-boot.bin with a image header.
- 2. Build
- --------
- To build U-Boot for the Gateworks Ventana product family:
- For NAND FLASH based boards:
- make gwventana_nand_config
- make
- For EMMC FLASH based boards:
- make gwventana_emmc_config
- make
- 3. Boot source:
- ---------------
- The Gateworks Ventana boards support booting from NAND or micro-SD depending
- on the board model. The IMX6 BOOT ROM will choose a boot media based on eFUSE
- settings programmed at the factory.
- Boards with NAND flash will always boot from NAND, and NAND-less boards will
- always boot from micro-SD. However, it is possible to use the U-Boot bmode
- command (or the technique it uses) to essentially bootstrap to another boot
- media at runtime.
- 3.1. boot from NAND
- -------------------
- The i.MX6 BOOT ROM expects some structures that provide details of NAND layout
- and bad block information (referred to as 'bootstreams') which are replicated
- multiple times in NAND. The number of replications and their spacing (referred
- to as search stride) is configurable through board strapping options and/or
- eFUSE settings (BOOT_SEARCH_COUNT / Pages in block from BOOT_CFG2). In
- addition, the i.MX6 BOOT ROM Flash Configuration Block (FCB) supports two
- copies of a bootloader in flash in the case that a bad block has corrupted one.
- The Freescale 'kobs-ng' application from the Freescale LTIB BSP, which runs
- under Linux and operates on an MTD partition, must be used to program the
- bootstream in order to setup this flash structure correctly.
- The Gateworks Ventana boards with NAND flash have been factory programmed
- such that their eFUSE settings expect 2 copies of the boostream (this is
- specified by providing kobs-ng with the --search_exponent=1 argument). Once in
- Linux with MTD support for the NAND on /dev/mtd0 you can program the SPL
- with:
- kobs-ng init -v -x --search_exponent=1 SPL
- The kobs-ng application uses an imximage which contains the Image Vector Table
- (IVT) and Device Configuration Data (DCD) structures that the i.MX6 BOOT ROM
- requires to boot. The kobs-ng adds the Firmware Configuration Block (FCB) and
- Discovered Bad Block Table (DBBT). The SPL build artifact from U-Boot is
- an imximage.
- The u-boot.img, which is the non SPL U-Boot binary appended to a U-Boot image
- header must be programmed in the NAND flash boot device at an offset hard
- coded in the SPL. For the Ventana boards, this has been chosen to be 14MB.
- The image can be programmed from either U-Boot or Linux:
- U-Boot:
- Ventana > setenv mtdparts mtdparts=nand:14m(spl),2m(uboot),1m(env),-(rootfs)
- Ventana > tftp ${loadaddr} u-boot.img && nand erase.part uboot && \
- nand write ${loadaddr} uboot ${filesize}
- Linux:
- nandwrite /dev/mtd1 u-boot.img
- The above assumes the default Ventana partitioning scheme which is configured
- via the mtdparts env var:
- - spl: 14MB
- - uboot: 2M
- - env: 1M
- - rootfs: the rest
- This information is taken from:
- http://trac.gateworks.com/wiki/ventana/bootloader#nand
- More details about the i.MX6 BOOT ROM can be found in the IMX6 reference manual.
- 3.1. boot from MMC (eMMC/microSD)
- ---------------------------------
- When the IMX6 eFUSE settings have been factory programmed to boot from
- MMC the SPL will be loaded from offset 0x400 (1KB). Once the SPL is
- booted, it will load and execute U-Boot (u-boot.img) from offset 69KB
- on the micro-SD (defined by CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR).
- While it is technically possible to enable the SPL to be able to load
- U-Boot from a file on a FAT/EXT filesystem on the micro-SD, we chose to
- use raw micro-SD access to keep the code-size and boot time of the SPL down.
- For these reasons an MMC device that will be used as an IMX6 primary boot
- device must be carefully partitioned and prepared.
- The following shell commands are executed on a Linux host (adjust DEV to the
- block storage device of your MMC, ie /dev/mmcblk0):
- DEV=/dev/sdc
- # zero out 1MB of device
- sudo dd if=/dev/zero of=$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 1MB
- printf "1,,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
- The above assumes the default Ventana micro-SD partitioning scheme
- - spl : 1KB-69KB (68KB) required by IMX6 BOOT ROM
- - uboot : 69KB-709KB (640KB) defined by
- CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR
- - env : 709KB-965KB (256KB) defined by
- CONFIG_ENV_MMC_SIZE
- CONFIG_ENV_MMC_OFFSET_REDUND
- - rootfs : 1MB-
- This information is taken from:
- http://trac.gateworks.com/wiki/ventana/bootloader#microsd
- 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 an EEPROM register on i2c-0 at 0x50:0x00:
- set to '0' will choose to boot to U-Boot and otherwise it will boot to OS.
- 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} - ${fdt_addr}
- # flash args (at 17MB)
- Ventana > nand erase.part args && nand write 18000000 args 100000
- # set i2c register 0x50:0x00=0 to boot to Linux
- Ventana > i2c dev 0 && i2c mw 0x50 0x00.0 0 1
- Be sure to adjust 'bootargs' above to your OS needs (this will be different
- for various distros such as OpenWrt, Yocto, Android, etc). You can use the
- value obtained from 'cat /proc/cmdline' when booted to Linux.
- This information is taken from:
- http://trac.gateworks.com/wiki/ventana/bootloader/falcon-mode#nand
- 4.2. Falcon Mode on micro-SD card
- ---------------------------------
- To prepare a Gateworks Ventana board with a primary boot device of micro-SD
- you first need to make sure you build U-Boot with CONFIG_ENV_IS_IN_MMC
- instead of CONFIG_ENV_IS_IN_NAND.
- For micro-SD based Falcon mode you must program your micro-SD such that
- the 'args' and 'kernel' are located where defined at compile time
- by the following:
- CONFIG_SYS_MMCSD_RAW_MODE_ARGS_SECTOR 0x800 (1MB) - offset of 'args'
- CONFIG_SYS_MMCSD_RAW_MODE_KERNEL_SECTOR 0x1000 (2MB) - offset of 'kernel'
- The location offsets defined above are defaults chosen by Gateworks and are
- flexible if you want to re-define them.
- First you must prepare a micro-SD such that the SPL can be loaded by the
- IMX6 BOOT ROM (fixed offset of 1KB), and U-Boot can be loaded by the SPL
- (fixed offset of 69KB defined by CONFIG_SYS_MMCSD_RAW_MODE_U_BOOT_SECTOR).
- The following shell commands are executed on a Linux host (adjust DEV to the
- block storage device of your micro-SD):
- DEV=/dev/sdc
- # zero out 1MB of device
- sudo dd if=/dev/zero of=$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 i2c register 0x50:0x00=0 to boot to Linux
- Ventana > i2c dev 0 && i2c mw 0x50 0x00.0 0 1
- 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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