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board/atmel: update documentation for SD card generation

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Henceforth, a sdcard.img file is automatically generated. It simplifies the
procedure to generate a bootable SD card for Atmel Xplained boards.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
This commit is contained in:
Ludovic Desroches 2016-04-08 16:30:41 +02:00 committed by Thomas Petazzoni
parent 89155c8492
commit ce86f9eaf2
1 changed files with 31 additions and 41 deletions
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72
board/atmel/readme.txt
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@ -119,51 +119,41 @@ Reboot, the system should boot up to the buildroot login invite.
Preparing the SD card
=====================
The SD card must be partitioned with at least two partitions: one
FAT16 partition for the bootloaders, kernel image and Device Tree
blob, and one ext4 partition for the root filesystem. To partition the
SD card:
An image named sdcard.img is automatically generated. With this image,
you no longer have to care about the creation of the partition and
copying files to the SD card.
sudo sfdisk /dev/mmcblk0 <<EOF
,64MiB,6
;
EOF
You need at least a 1GB SD card. All the data on the SD card will be
lost. To copy the image on the SD card:
This creates a 64 MB partition for the FAT16 filesystem (type 6) and
uses the rest for the ext4 filesystem used for the root filesystem.
/!\ Caution be sure to do it on the right mmcblk device /!\
Then, format both partitions:
sudo mkfs.msdos -n boot /dev/mmcblk0p1
sudo mkfs.ext4 -L rootfs -O ^huge_file /dev/mmcblk0p2
Note: the -O ^huge_file option is needed to avoid enabling the huge
files features of ext4 (to support files larges than 2 TB), which
needs the kernel option CONFIG_LBDAF to be enabled.
Mount both partitions (if not done automatically by your system):
sudo mount /dev/mmcblk0p1 /media/boot
sudo mount /dev/mmcblk0p2 /media/rootfs
Copy the bootloaders, kernel image and Device Tree blob to the first
partition:
cp output/images/boot.bin /media/boot/
cp output/images/u-boot.bin /media/boot/
cp output/images/zImage /media/boot/
cp output/images/at91-sama5d2_xplained.dtb /media/boot/
Extract the root filesystem to the second partition:
sudo tar -C /media/rootfs -xf output/images/rootfs.tar
Unmount both partitions:
sudo umount /media/boot
sudo umount /media/rootfs
dd if=output/images/sdcard.img of=/dev/mmcblk0
Insert your SD card in your Xplained board, and enjoy. The default
U-Boot environment will properly load the kernel and Device Tree blob
U-Boot environment will load properly the kernel and Device Tree blob
from the first partition of the SD card, so everything works
automatically.
By default a 16MB FAT partition is created. It contains at91bootstrap,
u-boot, the kernel image and all dtb variants for your board. The dtb
used is the basic one:
U-Boot> print
[...]
bootcmd=fatload mmc 1:1 0x21000000 at91-sama5d2_xplained.dtb; fatload mmc 1:1 0x22000000 zImage; bootz 0x22000000 - 0x21000000
[...]
If you want to use a variant such as the _pda7 one, you will have to
update your u-boot environment:
U-Boot> setenv bootcmd 'fatload mmc 1:1 0x21000000 at91-sama5d2_xplained_pda7.dtb; fatload mmc 1:1 0x22000000 zImage; bootz 0x22000000 - 0x21000000'
U-Boot> save
Saving Environment to FAT...
writing uboot.env
done
A 512MB ext4 partition is also created to store the rootfs generated.
If you want to customize the size of the partitions and their content,
take a look at the the genimage.cfg file in the board directory.