Espruino USB HID GamePad - v0.1a ready ! ( may also be Bluetooth & RN42 ready .. )

Nice! Thanks for the RN42 links and code!

wondering what was the best way to put a pin on "high impedance" ( floating ? )

As @allObjects says, literally just digitalRead(pin) should do it - or you can force it with pinMode(pin, "input")

STM32F3 Espruino USB

Honestly, no ideas. ST's USB stack is a mess with Espruino because they kept changing it - the F1 has a different stack to the F4, and while I think the F3 is similar to F4 I believe it's different enough that some decent size changes are required :(

Just IMO, but it's not worth it trying to target just because you have an F3 board. Spend £10 on an F4 board of some kind and save yourself weeks of pain :)

Shouldn't it work if "sizeof(struct gamepadHID_t)" equals to "HID_EPIN_SIZE" ?

You may find that GCC/whatever is padding the elements inside gamepadHID_t to 4 byte boundaries, which is causing your trouble? It looks like it's 6 bytes but it may get reported as 8. I'm not certain on that though