04-12-2020, 11:22 AM
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.