I do have an iPac-2 which I have been getting prepared to build into a cabinet with a Pi 2, and I have found that there are actually just a minor quirk or two to deal with. Specifically, the latest builds of retropie are using a Dispmanx-enhanced version of SDL by default for AdvMame, but I found that the games that required the mouse (i.e. Ultimarc spinner/trakball connected to the Ipac-2’s headers) did NOT work with this version of SDL – a mouse cursor appeared (unusual) but I couldn’t get the games to respond to the trak/spinner input. On the Pi 2, I think there’s little reason to use the Mame4all-pi version, the performance of Advmame is now entirely adequate on the Pi2. So I had to edit the advmame.rc file to specify a few things differently:
“device_video fb” instead of “device_video sdl”, also
“device_mouse raw” and “device_raw_mousedev[0] /dev/input/mouse0”
Can’t remember, might’ve also had to set “device_keyboard auto” if it was set to sdl as well.
Then the analog controls work great.