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)
==== Build a minimum USB master frames state-machine ====
Let's just plug a USB joystick on FPGA, permanently.
Objective here is to build a minimum state-machine graph, having for transaction between state a "frame transmission". It is normal on USB protocol to have error of transmission, so you have also to put "error frame transmission" on the graph.
At stabilisation, you finally switch between two states, one sending a certain frame that contains at different offset simply certain values of joystick button.
=== Why NEXYS2 500kgates starter kit ===
==== Xilinx schematics ====