Changes
/* Synchronize, decode and check USB frames */
Then using USB HID manual, you can understand type of frames, and author of them, and remark that the author alternate : USB master (PC) or USB slave (joystick)
You can use some "USB sniffer software" in order to understand more easily some frame contain, but they generally don't give all frame, and full frame.
==== Build a minimum USB master frames state-machine ====
Let's just plug a USB joystick on FPGA, directly, permanently, thinking about minimum coding size : we can't implement full HID USB protocol on FPGA ^^'
