Confusion abounds on the boot-up operation but I think if you have the Angstrom distribution that was labeled “eMMC flasher” then it will always re-flash the eMMC when you boot from it. I’m booting Arch Linux from an SD without issue, but to do so I booted to uSD and then mounted /dev/mmcblkp1 and deleted all the eMMC boot files. After that it just boots to the uSD card by default. I think you need to get the non-“eMMC Flasher” image of Angstrom and you can do the same with that. I did it briefly but decided I prefer to stick with Arch for my boards. I can’t recall now exactly where I got the non flashing image from though.
That should be /dev/mmcblk1p1 for the eMMC boot partition
Could you elaborate a little on how to delete the eMMC boot files? I got my Beaglebone today and I'm trying to boot from the micro SD and haven't been able yet. Thanks a lot.
I did not delete the eMMC files, just renamed MLO to MLO.xxx. That worked fine for me and should be reversible, although I have not tried that yet.
mount /dev/mmcblk1p1 mount
mv mount/MLO mount/MLO.xxx