A stupid question.
I have armbian on usb (32GB), libreelec on sd (32gb) and android on mmc (32 gb).
If the usb in not inserted the system boot on sd and on exit of libreelec i can reboot to android, but with usb inserted system boot always on armbian.
I don't want create a dual boot on usb for space reasons.
There is a metod for choose the boot device before system boot strap?