FEL/USBBoot

FEL is a mode of Allwinner chips. If the chips goes to FEL mode, the chip will be waiting for communication from PC though USB. The primary purpose for FEL is for flashing the NAND with the PC tool LiveSuit

Go to FEL mode
There are some ways to go to FEL mode.

on some A10 tablets the FEL key is the one labeled "recovery", some tablets don't have FEL key. On cubieboard the FEL key is the one under the USB OTG port.
 * Press the FEL key when power up

Almost all the A10 tablets can go to the FEL mode by the following instructions:
 * Go to FEL mode by combo key
 * 1) Power off the device
 * 2) Press and hold any physical key except the power key on the device (ie press and hold Vol+ key, still holding in 3 and 4)
 * 3) Press and hold power key for about 2s (power on the device, when powering on, if a key is pressed, the devices will not boot until key released or 4)
 * 4) Release power key and press power key 3 times (I usually just keep pressing the power key)

Fel-boot: https://github.com/sunxi-tools/sunxi-tools/blob/master/fel-boot.c
 * Use sunxi-tools