by summers » Sat Jul 27, 2019 12:14 pm
What disk boots depends on uboot.
If you look in /boot/boot.txt you can see its sets $this->bbcode_second_pass_code('', 'root=PARTUUID=${uuid}')
and uuid is set via $this->bbcode_second_pass_code('', 'part uuid ${devtype} ${devnum}:${bootpart} uuid')
So you could just rewrite that to point at the sD card.
Now can't rember how clever the BBB is at finding uboot. Think it may look at both the eMMC and the sD card, with presumably the eMMC first.
So so should just be a case of removing uboot from the eMMC and making sure its on the sD card. Then the root partition should be set to the sD card without any other action. You should be able to check this on the main BBB site ...