To generate a firmware, run (paths may differ):

$ make
$ ./unpack-firmware.sh R0.ROM /tmp/romfiles
$ sudo ./patch-firmware.sh files /tmp/romfiles # needs sudo
$ ./pack-firmware.sh R0.ROM /tmp/romfiles

After that, R0.ROM is patched and can load Rockbox.

rockbox.sh is a script to put into rockbox.zip. It's a small loader script
that sets stuff up.