Can't reinstall debian after breaking pre-installed OS

[Arwen]

@crownest, sounds like you did not update the u-boot on the eMMC. The original default OS on the eMMC would not allow booting from SD cards. That was fixed in one of the first updates. That update has the u-boot on the eMMC check and see if there is a bootable SD card. If so, try and boot off of it. I've tested it, it works. That allowed me to add a physical partition for swap on my eMMC by booting off the SD card.

Before the u-boot update, eMMC takes boot priority and if there is something bootable on the eMMC, (even if the OS is broken), use the eMMC.

Note for others: If the eMMC is blank or does not have the SoC signature for the second stage boot code, then the SD card is tried next for booting. The problem that can happen is the the eMMC has something, (even if OS is broken, so it's booted first by SoC priorities.