Debian on the DreamPlug, Part II
If you have [[debootstrapped the internal microSD card|ranticore/debianonthedreamplug_part2]], the vendor-supplied U-Boot config should serve you adequately.
To boot off of a USB stick, however, interrupt the boot sequence (if you don't have a JTAG/serial board at this point, go buy one immediately), and enter the following commands:
setenv x_bootcmd_kernel fatload usb 1:1 0x6400000 uImage setenv x_bootargs_root root=/dev/sdc2 rootdelay=10 saveenv reset
If you just want to testboot once, and don't want to make it permanent, omit the
saveenv. If you do want to make it permanent, consider removing the superfluous pings from the bootcmd, but be careful to escape semicolons and dollar signs instead of zealously copying and pasting.
If you haven't bothered putting a FAT partition with uImage on the USB stick, omit the
setenv x_bootcmd_kernel line.
Once you've booted Debian, you may wish to natively-debootstrap or copy your new partition to /dev/sda2 (which is what Linux will call the ext3 partition of your microSD card).
To then return to fully booting off of microSD so you can repurpose the USB stick,
setenv x_bootcmd_kernel fatload usb 0:1 0x6400000 uImage setenv x_bootargs_root root=/dev/sda2 rootdelay=10 saveenv reset