u-boot fast boot

https://github.com/ARM-software/u-boot/blob/master/doc/README.android-fastboot-protocol

  

	FastBoot Version 0.4
	----------------------
	The fastboot protocol is a mechanism for communicating with bootloaders
	over USB. It is designed to be very straightforward to implement, to
	allow it to be used across a wide range of devices and from hosts running
	Linux, Windows, or OSX.