usb-in-a-nutshell 英文版 USB协议太厚了，这个英文版资料对USB协议做了简单梳理。只做USB设备开发，可以直接先看这个。 (1) most of us are here to develop USB peripherals and (2) it's common to read a standard and still have no idea how to implement a device. So in the next 7 chapters we focus o