In order to boot Armbian from VIM3 with pre-flashed OS on eMMC you need to:
- Download Khadas Rescue tool for VIM3 and flash it to a spare SD card
- Insert SD card, attach USB keyboard + monitor or a serial console and boot into Khadas Rescue Tool
- Choose: Advanced -> eMMC -> Fast erase and Advanced -> Erase SPI Flash (Yes). Go back and select "power off"
Now you can boot Armbian from SD card and install to eMMC the standard way.
- some people are having troubles with booting with Petitboot loader. In case you have troubles too, you need to disable Petitboot by running fw_setenv skip_spiboot true in the command line of Petitboot
- On modern kernels adding “video=HDMI-A-1:1920x1080M@60D” to boot /boot/armbianEnv.txt (extraargs=) should force HDMI to 1080p instead of the 4K native resolution.