GP-Wiz40 MAX USB and RetroPie

Since I’m going to all the trouble to build a big screen movie setup in the backyard, I figured — games! And since I’m not a great fan of current games, I wanted retro.

With lucky happenstance, I ran across a Linux build for the Raspberry Pi (the $35 computer) that is designed for retro gaming in mind. Horray! It’s called RetroPie (and yes, there are others).

The current build is quite nice, with everything installed. But how to control it? I got some cheapie USB controllers (SNES style) that will work, but I wanted heavy duty. And what about MAME? That app, for all it’s greatness, is so bound to a keyboard. And I don’t want a keyboard on my back porch.

For past projects (not completed) I had purchased a couple of interface boards from GroovyGameGear. Their GP-Wiz 40 — a device that is seen as a game controller, and connects via USB. That would work great for controllers. (Again, from past projects, I have arcade quality sticks and buttons on hand, from X-Arcade.)

The other product I have of theirs is their KeyWiz — which emulates a keyboard. It’s a great product with a fatal flaw (in the case of the Raspberry Pi) — it uses a PS/2 port. No PS/2 port on the Pi. And that port is, unfortunately, as rare as hens teeth on current PCs.

KeyWiz would be perfect for MAME, since it acts like a keyboard, not a gamepad/joystick. However, the port limitation means I can’t use it.

So, back to the GP-Wiz 40. Good news: The EmulationStation front-end to the emulators pick it up fine. But what about the emulators themselves?

You really go down the rabbit hole with this stuff.  Here’s how it works:

  • EmulationStation is a pretty front end to start the emulators and games. It does not actually do the emulation. It’s your “TV GUI”.
  • RetroArch is a middle layer. It gets called from ES and handles the calling of the individual emulators. Why a middle layer? Well, for one, it makes coding front-ends easier. ES just has to interface with RA, not a bunch of individual emulators. And, you can choose to config controllers once — in RetroArch — and it passes those configs down to the emulators.
  • The emulators themselves. These are custom builds for the PI to take advantage of its meager resources. Keep “custom builds” in mind — because of the heartache these will cause (below).

I mapped the GP-Wiz 40 inputs to various controls in RetroArch. For example, Linux Joystick Button 4 = “A”, Button 5 = “B”, Button 16=”Select” and so on. For NES and SNES I needed 8 inputs (U/D/L/R/A/B/X/Y) for the usual controls, plus 2 more — for Select and Start.

That all worked fine. I got NES, SNES, and Atari 2600 working fine. Good progress. But what about MAME — for the arcade games?

Well, this was (and still is) a bear. For one, the mappings I setup in RetroArch didn’t seem to translate to the MAME emulator (MAME4ALL). Well, there are worse things, I guess. I can manually do the mappings within MAME.

Couple of issues:

  1. The config stuff is read-only. So if you change settings, they don’t stick after a MAME restart. Saw this with RetroArch, too. This is fixed by changing the ownership of the config files to the “pi” user. Something like “sudo chown pi retroarch.cfg” (sudo=act as admin, chown=change owner, pi=new owner, retroarch.cfg=file you want owner changed on).
  2. I could not, for the life of me, get MAME to recognize the joystick ports (analog, but can be used as digital). So, I had to go with pure digital.
  3. I could not get MAME to recognize all of the digital ports on the GP-Wiz 40. This really, really sucked.

Why did #3 suck so bad? Because MAME uses all those damn “insert coin” and “player one start” stuff to start a game. So, in addition to the regular buttons, I needed ports for that (remember, I don’t want a keyboard outside).

The GP-Wiz 40 has plenty of ports — so why didn’t MAME recognize them? Well, after seeing nothing in the documentation, I came across this is a change log: “Updated code to support 16 buttons”.


Player 1: U/D/L/R/A/B/X/Y = 8 + Player 2 is another 8 — 16. I’m maxed out, because this custom build limited buttons.

So, I could get game controls in MAME, but can’t actually start a game. And so it stands right now. Either I have to figure out how to get the joystick analogs to work, freeing up 4 digitals for each user, or come up with some sort of magic hotkey. (In the SNES and NES emulators, since they can see more than 16 buttons, I have dedicated digital lines for Select and Start — and pressing them together exits the emulator.)

So, if you are wanting to use the GP-Wiz 40 for two players in RetroPie, keep this in mind: SNES and NES and Atari 2600 (the ones I tested and have games for) work fine. I’m using digital for the joystick, but since I have plenty of ports, no problem. MAME is the problem, with it’s limitation. Like I said, I’m still working on it, and I’ll post again if I come up with a solution.