the ipac 2 player acts just like a normal keyboard with the default mame keyboard keys mapped on the pins. if you want to change the mapping, there is also an editor for that on pc, mac and linux. hope this helps.
Hi, Here you have the default key code mapping. http://www.ultimarc.com/ipac2.html So you just plug a normal keyboard on your pi first and with the ému your interested in you map control with the same key codes. Once is done you can plug your I-Pac2 and Voilà! :-D
You Need to go inside the snes9x.cfg file Here you will find the key mapping (numbers instead of "key_D" for exemple) /usr/include/SDL/SDL_keysym.h Here is were you'll find which key for which number used in the mapping