===== USB mode: USB1 or USB2; low speed, full speed or high speed =====
For sampling, I speed up five times the saving speed on RAM. I succeed sampling an USB1 transmission: "Logitech dual action USB joystick", and an USB2: "Sony PS3 USB joystick". PS3 joystick is not stable enough with my FPGA, but Logitech joystick is correct.
http://www.youtube.com/watch?v=2zEp1tHroBs
http://www.youtube.com/watch?v=fh4v4OXridc
===== pull up and pull down =====
If you respect USB protocol, you have to plug some pull-up and pull-down resistors and some capacitors. But as I am a bad electrician, I just simulate then in VHDL, they are important because they cause USB speed negotiations. You also have an electronic mechanism in order to detect presence of joystick plug, I don't care about it.