Signed-off-by: Tim Harvey tharvey@gateworks.com --- board/gateworks/gw_ventana/README | 74 +++++++++++++++++++++++++++++++++++++-- 1 file changed, 71 insertions(+), 3 deletions(-)
diff --git a/board/gateworks/gw_ventana/README b/board/gateworks/gw_ventana/README index 888657c..74698b7 100644 --- a/board/gateworks/gw_ventana/README +++ b/board/gateworks/gw_ventana/README @@ -3,6 +3,12 @@ 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) ---------------------------------
@@ -28,8 +34,20 @@ To build U-Boot for the Gateworks Ventana product family: make
-3. Boot source, boot from NAND ------------------------------- +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 @@ -77,7 +95,57 @@ via the mtdparts env var: - rootfs: the rest
This information is taken from: - http://trac.gateworks.com/wiki/ventana/bootloader#NANDFLASH + 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 micro-SD +----------------------- + +When the IMX6 eFUSE settings have been factory programmed to boot from +micro-SD 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 a micro-SD 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 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 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.