In order to flash the OS into eMMC with USB Upgrade Tool, you need to put the board enter Upgrade Mode.
There are 4 ways to boot into upgrade mode:
Function key 3 times in 2 seconds, then release the key. You will see the Power LED (Red) blink for about 3 seconds.
POWER key without releasing it.
RESET key and release it.
POWER key to enter into Upgrade Mode. The Sys LED (White) will turn on when you’ve entered Upgrade Mode.
SPACE on your keyboard at the moment of bootup to stop autoboot. This step will let VIM4 boot into U-Boot command line.
run update in the terminal of U-Boot then the board will enter Upgrade Mode.
SPACE key at the moment of bootup to stop autoboot. This step will let VIM4 boot into U-Boot.
run update in the U-Boot terminal.