I bought a Pandora Box and was playing with it for a while, but didn't like that I couldn't add games myself. So I replaced the Pandora board with a Raspberry Pi 4.
I wired up the joysticks using the GPIO pinout from https://github.com/recalbox/mk_arcade_joystick_rpi
The Pandora uses a 40 pin connector, so I purchased a 40 pin breakout cable to rewrite the 40 pin to the GPIO on the Pi.
After wiring up the GPIO, I made a modprobe.d config to load the driver with 2 controllers.
options mk_arcade_joystick_rpi map=1,2
Emulation station then recognised my controllers, and I was able to configure each within Emulation station, but when I started a game, libretro would pop this message up:
GPIO 0 Configured
GPIO 1 (1/2) Not Configured
After messing around for a while, I found that I needed to configure the controller within retroarch.
I had to go to Settings → Input → Port 2 Controls
Now when i start games, I see that both GPIO controllers are configured and working.
The GPIO connected: