http://code.google.com/p/beagleboard...gleBootHwSetup -› "Beagle Board Setup for MMC booting"
Understanding MLO and X-loader
"MLO is just a signed version of x-loader using omap3430gp-signer.pl"
"You can find documentation for ROM code initialization/booting in the TRM
(spruf98b.pdf) chapter 25.4...
The MMC/SD card booting in particular is described in chapter 25.4.7.6..."
http://elinux.org/BeagleBoardRecovery
"Press user button at power up and according to above boot order MMC boot is before NAND. "
Исходники x-loader:
http://git.omapzoom.org/?p=repo/x-loader.git
Надеюсь, что-нибудь из этого поможет.