On supported Allwinner SoCs it is possible to boot over USB OTG. This requires only minimal changes compared to the build steps in the manual build howto, and these changes are explained on this wiki page.| linux-sunxi.org
FEL is a low-level subroutine contained in the BootROM on Allwinner devices. It is used for initial programming and recovery of devices using USB.| linux-sunxi.org