Commit 40e999ca authored by Tim Harvey's avatar Tim Harvey Committed by Stefano Babic
Browse files

imx: ventana: update README for micro-SD boot medium


Signed-off-by: default avatarTim Harvey <tharvey@gateworks.com>
parent 0a9c2150
......@@ -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.
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