What is it?

It's a Game Boy cartridge which utilizes the PIO state machines of the RP2350B (the MCU from the Raspberry Pico) to provide the ROM data to the Game Boy.

The Gameboy displays the list of files on the SD card. After selecting a ROM it is loaded and the Gameboy restarts with the selected ROM.

Do savegames work?

Yes, saves can be stored on the SD card. But saving cannot be done immediately like in original cartridges with battery backed RAM. In order to store the game the button on the cartridge needs to be pressed. This will write the savegame to the sd card. No restart of the Gameboy is needed. I have a plan to implement an autosave function, which stores the savegame after a period of time. But this is not implemented yet.

Is there support for real-time clock?

Yes. There is a coin-cell battery on the cartridge that lets the RTC tick while the gameboy is off.

Do I need a coin-cell?

Only if you want the clock to tick while the Gameboy is off. There are not a lot of games that support this. The cartridge will work fine without it. A coin-cell is not included in this offer. You can use any CR1225 coin-cell.

Limitations

The RP2350B cartridge does not work like a normal cartridge. It just emulates one. That does work on a normal Gameboy. But as soon as the signals deviate from the original Gameboy it does not work. That is true for most clones like the FPGBC. Sadly they do not behave like the original.

The double speed mode of the GBC does not work on older Gameboy Color revisions. Read more about this here and check if your GBC is compatible if you want to play ROMs in Color. DMG games do work.

The power draw of this cartridge is 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. Savegame support is 128k max, which enables the cartridge to load chiptunes.

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, sd card 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 had made simpler version with an RP2040 in the past. But it was always lacking some features. As soon as I heard about the RP2350B with more pins I immediately began designing this new cartridge, sporting a sd card and a battery-backed RTC.

What makes it special?

It's Open Source.

Remarks

While the current state of the software is functional, the development is not finished yet. There are quite a couple of things that should be improved:

• Long filename support for FAT
• Folder support (right now only the files on root are displayed)
• Autosave
• Backups of savefiles
• Optimize ROM loading speed

Therefore buying this cartridge is only advised if you are not afraid to flash a new software to it eventually (you cannot break it). You should be aware that the experience is not as well-rounded as it could be. You are of course invited into helping in development of the software. It's written in Rust.