What is it?

It's a Game Boy cartridge which utilizes the PIO state machines of the RP2040 (the MCU from the Raspberry Pico) to provide the ROM data to the Game Boy.

The mounted flash is 16 MB which allows for a couple of ROMs to be flashed on the cartridge. A simple bootloader enables you to select the ROM you want to play.

Flashing/Changing the ROMs is done through a fairly new technology called WebUSB. A webapp to manage the ROMs (and savegames) is provided.

Do savegames work?

Yes, saves can be stored on the flash. But saving cannot be done immediately like in original cartridges with battery backed RAM. If cartridge detects that the savegame is modified by the game the LED will light up in red. In order to store the game the button on the cartridge needs to be pressed. This will reset the cartridge (and the gameboy). On startup the savegame gets stored onto the flash. The LED will show successful storing by lighting up in green.

Limitations

Timings in the Gameboy Color's double speed mode are really tight because of the QSPI flash. It works on the Gameboy Color itself, but somehow not on the Gameboy Advance compatibility mode for now.

The power draw of this cartridge is significantly higher than normal cartridges. The normal Game Boy and Game Boy Color can handle this. But the power budget might be tight if further mods are installed (IPS screen, sound mod, backlight). It's old hardware and your capacitors may have aged differently so your results may vary. TLDR: If combined with Game Boy mods, consider also upgrading the power supply (eg CleanJuice).

Does LSDJ work?

Yes, in normal speed mode. Savegame support is 128k, which enables the cartridge to load chiptunes. With the webapp the savegame and with that the chiptune can be exchanged from the PC.

Which browsers are supported by the Webapp?

Chrome, Chromium and Edge officially support WebUSB and I have tested those successfully. Chrome and Chromium also works on Android, so the ROMs can be exchanged from a smartphone on the go.

Is the cartridge shell special?

No, the PCB will fit any standard shell. Any shell from an old original cartridge, a remade one from Ali* or from your local retro shop will work. Just get some pliers and cut some space for the USB-C connector and drill a hole for the button if you want to trigger storing of savegames. Where are options to add shells to the order. Precut shells are ready to use with the cartridge, while uncut shells have to be modified by yourself.

Is a cartridge shell needed?

Yes, it's needed. The PCB itself is too thin to make a connection with the connector in the Gameboy without it. It's by design, it would be too thick with a shell otherwise. But any shell is fine.

Why did you make it?

I wanted to test the PIO statemachines and was searching for a project to properly utilize them. And I like the Game Boy.

What makes it special?

Well it's kinda cheap. And it's Open Source.