Boot setup

The uBoot bootloader normally boots the OS from NAND, but it can be inhibited by pressing R while starting up to for example pick SD-card booting. This can also be set up with text-files, making it the default behaviour.

Set up your boot.txt

Create a new file called boot.txt (or autoboot.txt if you want to boot automatically) and copy and paste the text below. Copy that file to the root of the root of the SD card.

boot.txt (from the official firmware site)

setenv bootargs root=/dev/mmcblk0p1 rw rootwait vram=6272K omapfb.vram=0:3000K mmc_core.removable=0
ext2load mmc 0 0x80300000 /boot/uImage
bootm 0x80300000

Note: If you chose ext3 instead of ext2 for the partition containing the kernel, the second line still starts with ext2load. There is no ext3load.

Note: depending on firmware version kernels might be at several, sometimes multiple locations, so you have to choose one:

• /boot/uImage-3 - the default 3.2 kernel (recommended)
• /lib/boot/uImage - alternative location of 3.2 kernel on certain older firmwares
• /boot/uImage - mostly a symlink to the latest kernel on recent firmwares

Be aware though that this boot.txt assumes you have formatted your card with ext2 and loads the kernel off the SD card. It is technically possible to boot the kernel from NAND but still run the rest of the file system from your SD card with following boot.txt

setenv bootargs root=/dev/mmcblk0p1 rw rootwait vram=6272K omapfb.vram=0:3000K mmc_core.removable=0
ubi part boot && ubifsmount boot && ubifsload ${loadaddr} uImage && bootm ${loadaddr} && boot

However this is not recommended because kernel modules on SD card will likely be not compatible with kernel on NAND.

Both boot.txt's assume you are booting from the left SD card slot, first partition. You can change "mmcblk0p1" to "mmcblk1p1" if you want to boot from the right slot (but boot.txt must still be on a card on the left slot).

Rescue console boot

If you have a problem booting, and need to rescue data from the NAND) you can boot into a console by doing the following: Make a file named boot.txt in root of SD with this[1]:

setenv bootargs ubi.mtd=4 ubi.mtd=3 root=ubi0:rootfs rootfstype=ubifs rw rootflags=bulk_read console=tty0 vram=6272K omapfb.vram=0:3000K init=/bin/bash
ubi part boot && ubifsmount boot && ubifsload 0x80300000 uImage && bootm 0x80300000 && boot

then hold down the right shoulder button on boot and booting from the SD card. (It doesn't require an operating system on the SD card, but it will use the boot configuration specified there). This is a text mode boot to the shell, using the kernel from the NAND. This should provide a way of bypassing any broken startup scripts, adding in logging for a normal boot, etc. It does not start the full OS, just a basic shell.

Setting up multiple-partition SD cards for booting

It is possible to have several partitions on the SD card and boot from one of them. E.g. if you have three partitions on the card like this:

• Partition 1: FAT
• Partition 2: ext2 (where the rootfs should be placed)
• Partition 3: swap

How it's done:

1. Put uBoot's boot control files "boot.txt" and/or "autoboot.txt" into the root of the first partition of the card (FAT partition in this example)

2. Make "boot.txt" and "autoboot.txt" point U-Boot to the partition, which holds the root file system of your Linux system. This would be parition 2 in this example (ext2 FS). This is done using the "root" parameter of setenv.

3. Make "boot.txt" and "autoboot.txt" point U-Boot to the correct location to boot your kernel from. This kernel location can be any FAT or ext2/3/4 partition on the SD card. The uBoot commands "fatload" and "ext2load" with their parameter "mmc x:y" are repsonsible for loading the kernel. Choose the command, which addresses the file system the kernel is located on and make sure to correctly adapt the values x and y.

This common example boots the kernel from the FAT partition (then this is a "boot partition"), and uses the ext2 file system as root FS:

setenv bootargs root=/dev/mmcblk0p2 rw rootwait vram=6272K omapfb.vram=0:3000K mmc_core.removable=0
fatload mmc 0:1 0x80300000 uimage
bootm 0x80300000

If you put the kernel into the root file system's /boot directory, the second line would be different:

setenv bootargs root=/dev/mmcblk0p2 rw rootwait vram=6272K omapfb.vram=0:3000K mmc_core.removable=0
ext2load mmc 0:2 0x80300000 /boot/uImage
bootm 0x80300000

Note:

For both the "root=" kernel argument and the "mmc x:y" argument of the fatload/ext2load commands, slot numbering begins at 0 (0 is left SD slot, 1 is right SD slot) and partition numbering begins at 1!

Recommendation:

Put the kernel into another partition than the root FS is located. Reason: In case the root FS partition is flagged "inconsistent" after a system crash or sudden SD card removal, uBoot won't be able to boot from that partition anymore. But the file system cleanup routines can only be run, once the kernel has been booted. Hence it's safer to put the kernel on a different partition.

If you want to use ext4 for the root FS, it is necessary to put the kernel on a different partition.

Options Summary

Files	File System Options	Location
boot.txt/autoboot.txt	FAT, ext2, ext3	first partition of left SD card
kernel	FAT, ext2, ext3	parameters of fatload or ext2load
rootfs	ext2, ext3, ext4	"root" parameter of setenv

Boot the system

As you power up the Pandora, hold the shoulder button R. A menu should appear, allowing you to boot from the SD card. (this step isn't necessary if you chose to create an autoboot.txt instead of boot.txt). Remember that this will be an un-configured image, taking a little while longer to boot, and giving the first-run dialogue.

Access the NAND

Once you're booted into the system from SD, you may want access to the NAND rootfs. The following will let you do that.

sudo mkdir /mnt/nand
sudo ubiattach /dev/ubi_ctrl -m 4
sudo mount -t ubifs ubi0:rootfs /mnt/nand

Extending intall environment

An alternative approach to using an SD card to increase the space accessible to the system is OS Extend. This allows the root filesystem to exist on more than one physical device.

References

• Official firmware page
• The GUI-driven SD installer by David Boucher

Copy the files to your SD card

Navigate (cd) to the directory with the .tar.bz2 file you just downloaded (or made) and do:

sudo tar -xvjf <tarfile>.tar.bz2 -C <SD card>

If you're doing this on your Pandora, <SD card> is something like /media/mmcblk0p1 (first SD card slot on Pandora). On Ubuntu it would be something like /media/disk if it has no label. You can also try using GUI tools for this, but I didn't have very good luck with them.

OR copy your firmware from the NAND to the SD card

The following will ask for your password. All the operations need root permissions so I thought it would be wasteful to sprinkle sudo to everything. We will bind mount the root fs to an alternative location ("/mp"), under which other filesystems mounted under root (like the kernel virtual filesystems /proc and /sys, and your SD card.) wont be visible. This allows us to take a live copy of the NAND contents to the SD filesystem.

sudo su
mkdir /mp
mount --bind / /mp
cp -va /mp/* /media/<SD card>
umount /mp
rmdir /mp
exit

serial port

In an unlikely event that you can get serial output from EXT port, be aware that serial device has changed several times (due to the driver and port configuration changes in the kernel):

• openpandora.org 2.6.27: ttyS0
• mainline upto 2.6.36: ttyS2
• mainline/openpandora.org 2.6.37 and up: ttyO2

This is relevant for console= bootarg.

MLO bootloader

Holding START while switching it on will only work if you have a bootable SD Card with a special MLO bootloader in the left SD slot, as this forces the Pandora to boot from SD.

In the case of a broken R button

The file that kicks things off is boot.scr. Place an autoboot.txt file on the SD card to trigger an automatic boot off the SD card without having to use the right shoulder button. Create autoboot.txt file that would load the boot.scr file and start the reflash :

setenv bootcmd  ’mmc init;fatload mmc 0 0x82000000 boot.scr; source 0x82000000’

Thanks to user limxr [2]

SEE ALSO

urjaman github u-boot DjWillis distant earth boot documentation