How to boot to a debian system on a usb flash drive

This guide may be redundant but having spent hours in digging through various posts I felt it could be useful. I tried with 9G20 board but I think it could apply to other board.

Glomation SBC board is by default configured to boot to an emdedian file system that stored in Flash. I think it's preferable to boot to a USB drive that has a debian system. Here is how I did it after consulting the posts in the forum.

Prepare the usb drive on your PC
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My PC is running linux Mint 8,

- Format your flash drive to ext3
sudo fdisk /dev/sdb1
sudo mkfs.ext3 /dev/sdb1

- mount your flash disk
sudo mount /dev/sdb1 /mnt

- download debian etch image for gesbc
http://www.glomationinc.com/download/debian-etch-arm-base.tar.gz

- load the debian file system to your usb drive
tar xzvf debian-etch-arm-base.tar.gz /mnt

Change U-boot environment setting
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Now insert your usb drive to your sbc then power up the board. stop the U-boot by pressing any key,

The printenv command can print out all current U-boot environment variable settings. The set command can be used to set the environment variable for example,

set bootargs console=ttyS0,115200 root=/dev/sda1 rootdelay=10 mtdparts=atmel_nand:1M(bootloader),3M(kernel),-(rootfs)

to set the boot argument to use USB as root file system. Note the sbc recognize the usb drive as /dev/sda1 on my board (while it was recognized /dev/sdb1 on my PC). Please note the MTD device name of the NAND FLASH is at91_nand for kernel version 2.6.25.x and atmel_nand for kernel version 2.6.27.x and up.

You can save the setting use saveenv command so the board can boot using USB root file system as default.

Other Useful Tips
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- Route debug message to UART (P1)

I find someone in forum says "I was shocked by the fact that the debug message is not routed to the UART (P1) port of the board, but to a 3-pin P0.". I have the same feeling here.

You can remove this inconvenience by changing the U-boot environment setting to route it to UART (P1)
set bootargs console=ttyS1,115200 root=/dev/sda1 rootdelay=10 mtdparts=atmel_nand:1M(bootloader),3M(kernel),-(rootfs)

remember to save the setting use saveenv command. then type boot and connect your NULL modem from your PC to the sbc board.

In production, you can easily switch it back.

- Setup a SSH server

Actually, you rarely need look at the debug message. If you setup the SSH server on sbc board, you can even get rid of the NULL modem cable, just connect the board using ssh.

To install ssh server, type
apt-get install ssh

Issues
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I find the default dhcp client shipped with emdebian has a short timeout. When dhcp server is slower in response, the board ends up with "discover... discover... fails". However, the debian system 's DHCP client wait longer which then correctly configures the network, thus allows for ssh access without any user intervention.