Here's my finished arcade gaming cabinet--with RetroPie the controls would not work. In desperation, I installed Recalbox and low and behold everything just worked PERFECTLY. Bravo, Recalbox! This display is from a non-working iMac, btw. The post explaining more about it is located here.

When I try to play a game in the libretro FBA emulator, only the start button works--A and B do not. The joystick does work. These buttons work perfectly in the NES emulator. Any thoughts?