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.
===== pull up and pull down =====
If you respect USB protocol, you have to plug some pull-up and pull-down resistors and some capacitorcapacitors. 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.
==== Synchronize, decode and check USB frames ====