Busy completing my bartop arcade at the moment. had to redo my setup for the 2.4 image of retropie. but it definitely does work.
i have 4 buttons for each joystick, 6 buttons for each player + additional start and add coin buttons for each player. total of 24 buttons.
there is some setup required, im using Adafruit-Retrogame, which is another version of retrogame which is what osnoogie posted.
easy way to test is wire the buttons up, once you have done the retropie setup (not forgetting the modprobe uinput) you can just call ./retrogame from the command line and press the buttons, it should pick up. you can then open retrogame.c and change the button mappings.
Will that wiring setup, and using the GPIO be compatible with all other emulators (NES, SNES, Sega, ATARI, etc)?
I’m pretty new to the whole Lixux/Debian based programming and have completed building a full, 2-player arcade cabinet based on Lusids Arcade Flashback design. I’ve been fighting like mad to get it to work with an iPac2 controller (which RetroArch will not recognize at all for programming keys) and am seriously looking at wiring it directly into the GPIO.