主要研究usb host的数据传送问题，里面有对 相关usb传送关系进行解析，并对 关键函数 ： //first field ox21 is bin 00100001 which splits into 0 01 00001 for direction(1bit)/type(2b)/recipient(5b) //To set direction as 'host to Device' we need 0, To set type to HID we need 11 (3), and for recipient we want 00001