NanoPi M4V2: Force boot from SD card

[mmriech]

When booting the NanoPi M4V2 a emmc has higher priority than a SD card. This is usually fine but if I want to replace the OS on the emmc the easiest way is to boot from the SD card and do the work from there. But how can I "force" the device to boot from the emmc?
What works: Pull out the emmc, start booting from SD and push the emmc in a couple of seconds later. This way it is not booted but detected by the OS.
But that's a hack and usually required multiple attempts until the OS boots from SD card. Is there a more elegant way to boot from the SD card?

[v8dave]

I don't have that board but what happens if you hold down the recovery key during boot?

[mmriech]

I don't have that board but what happens if you hold down the recovery key during boot?

Assuming it's the button right next to the ethernet connector: Short story: Same as not pressing the button.

Long story: EMMC is connected, operating system installed. SD-card is inserted, operating system installed. I press and hold the button, then I connect power to the board. As soons as the green led flashes (signals boot complete) I release the button. The OS that has been booted is the one of the EMMC.

By the way: Installed OS on EMMC is Armbian 19.11.4 with legacy kernel. Installed OS on SD-card is Armbian 19.11.4 with current kernel.