Code for a Pi Pico to read a CD32 gamepad and output each control to a separate pin for use with Neo Geos and/or Superguns.

I am personally using this code with a Monster Joysticks CD32 joystick and a Minigun Supergun. I don't know if it works with anything else.

Aspirationally, this will also read a Mega Drive/Genesis controller (fairly simple), and possibly USB controllers (a lot more complex, and projects to do it already exist). I also intend to create a PCB that uses a bare RP2040 chip to make things a bit neater and easier to hook up.

• A Pi Pico or compatible device that exposes the GPIO pins
• (Optional, but recommended) a level shifter for shifting the three signal pins going to the CD32 pad
• A DE9 and DA15¹ connector (ideally plug for DE9, socket for DA15)

Take a look at the code to see how to wire this up (it's currently different from the schematic, which I'll update later, it's not a priority given I'm the only person using it).

Add a bidirectional level shifter for 3.3V to 5V between the Pico and pins 5, 6, and 9 of the DE9 to be on the safe side.

Build and install the firmware and you should now have a Neo Geo/Supergun-compatible output from your CD32 controller. If the buttons are wrong or not to your taste, either move them on the DA15 side - each button has a direct mapping to a single pin there - or modify the code to use different GPIOs for the output pins.

This code theoretically also copies signals from up/down/left/right through the GPIO system, but for just the CD32 support it's not needed so I wouldn't bother.

This is based on the rp2040 project template, have a look there for details. You need a rust build environment and the project will build with Cargo.

This polls at 125Hz - I don't know whether a real CD32 pad will be happy with this, but I don't see why it wouldn't. The timing for each polling burst is based on what I observed with my PAL Amiga 500+, so that should be fine, but it was only polling at 50Hz. Given how little time is spent polling compared to waiting even at 125Hz, though, I can't imagine what issues might arise.

Thanks to Mathew Carr's PSCD32 Development Diary for documenting how the CD32 protocol actually works.