Modifying U-Boot scripts
The main useful script is gumstix-factory.script which, if found on the MMC or CF card will be executed during boot.
To generate a u-boot script that's executable, it has to be packed into an u-boot image using mkimage.
Use your favorite text editor (such as vi, nano, or pico) to create gumstix-factory.script.source, and then run the following command to generate the image:
mkimage -A arm -O linux -T script -C none -a 0 -e 0 -n gumstix-factory.script -d gumstix-factory.script.source gumstix-factory.script