How to enter MarsBoard A10/A20 FEL mode
From wiki
FEL Mode on MarsBoard A10/A20
Note: The Uboot key is the ESC key.
Board not powered on
If the board is not powered on, to switch MarsBoard A10/A20 to FEL mode, simply press and hold the Uboot key (ESC) and connect the USB OTG cable to your PC. The board will turn on emitting a red light and will stay on FEL mode waiting for commands.
Board is powering on
When the board is power on, you can plug the OTG cable to your PC first and then one finger press and hold the Uboot key (ESC), another finger press the PWR key. After 5 Second, the board will shutdown, you must press and hold the PWR key again, The board will turn on emitting a red light and will stay on FEL mode waiting for commands.
