Err,, I am more and more convinced that mrfixit's Uboot is the best
If mrfixit will boot from SD, it's really simple
(note /dev/emmc = /dev/mmcblkX, be sure to use lsblk to get RIGHT X)
1 Save mbr or gpt mbr (the mbr on emmc),, either sector 0 or sector 0-33 (using dd of course)
2 dd if=/dev/SDcard of=/dev/emmc bs=1M count=16
3 sync
4 restore mbr or gpt mbr, again using dd
If mrfixit will boot from SD, it's really simple
(note /dev/emmc = /dev/mmcblkX, be sure to use lsblk to get RIGHT X)
1 Save mbr or gpt mbr (the mbr on emmc),, either sector 0 or sector 0-33 (using dd of course)
2 dd if=/dev/SDcard of=/dev/emmc bs=1M count=16
3 sync
4 restore mbr or gpt mbr, again using dd