No problem ! Yesterday i was able to achieve what i wanted to do configuring correctly joytokey, so don't spend some time on this !
Though i may have something to submit to you. I noticed a strange behavior between Super Pause and Mednafen. As stated before i play on an old CRT TV using native resolution. I use a fork of mednafen named emu4crt that can output real native resolution. When playing game with mednafen and calling super pause, instead of staying at the same resolution of the current game, Super pause switch resolution back to the desktop resolution. When i resume to the game, mednafen's resolution is screwed, and i have to exit full screen and get back to fullscreen to recover the right resolution.
It only happen with mednafen. While playing with other emulators (retroarch, dolphin, pcsx2), Super pause stay at the current emulator resolution and there's no problem when resuming to the game.
Mednafen is the only emulator using Opengl as backend, do you think it's something related ?