Changing the boot loader

[Boern]

Does anyone know what kind of possibilities we have to change the boot loader? I mean whatever is running before the OS is starting right now it seems to look for something to boot on the sd card first and then on the emmc. I would love it if it were possible to choose where it is booting from, maybe by holding down one of the volume keys.

I guess this lies somewhere in the /dec/mmcblk2boot0 and /dev/mmcblk2boot1 devices. But they just seem to be 4 MB of zeroes.

So, does anyone know anything source code with build and flashing instructions would be top.

[wibble]

As I understand it the part that checks the uSD then the emmc is hardcoded into the A64 cpu. The bootable images so far use uboot as the stage this bootloader finds, and this then loads the linux kernel. I don't know if you could get the input from a customised uboot, or whether you'd need to go via a minimal linux. I've seen the instructions for modifying the uboot in another forum post, but can't seem to find it just now.