dkart

An open-hardware and software Gameboy flash-cart and hardware peripheral framework that uses off-the-shelf hardware. The goal is to be ultra-cheap and simple.

quickstart

If you just want to get started, go to releases and grab dkart.gb, and put it on a FAT32-formatted SDCard. Solder together the hardware, plug it in, and startup your gameboy.

Hardware

It's meant to be very cheap & easy to put together. I made a PCB, and you can just solder in a cheap ESP32 board and the SDCard shield, and it should work.

Originally, I designed this as a custom circuit with really low-resource chips, but realized it was much easier and cheaper to just use more modern ready-made stuff.

Eventually I'd like to add an i2c bus that can be triggered/read from gameboy, so users can easily mess with hardware peripherals.

I am still working on the PCB & schematic. You can open hardware/Dkart.json at easyeda.

under consideration

Here are some other ideas I am looking at:

• STM32F401
• This board has a SDCard and OLED screen (and wifi/bluetooth)
• cheap atmega2560 board, works with arduino & has more IO/RAM/CPU, but still not big enough to hold every ROM
• fast flash mem - I could load the rom & ram into flash temporarily on a lower-end microcontroller, then feed the data to the GB.
• something like this has a lot of storage (32GB) but might not be fast enough
• ready-made cart PCB - with a little simple soldering and a big flash chip, I could probly get it all to fit inside a cartridge
• something like this could be hooked up directly to GB pins, with maybe a little simple mode-management from a micro
• sdfat can do 3965.11 KB/Sec transfer in dedicated SPI with a slow cad, which should be fast enough
• better SDCards can go much faster, so make sure to check SD speed (SDFst has a bench sketch)
• 3d print longer cart to hold more electronics if needed. here are some nice variations. Here is a nice modular design (opnscad - chnage logo, etc)
• I have a ATxmega128A1 breakout laying around, but it's discontinued at sparkfun. It has 78 IO and 32 MIPS! It only has 128kB of flash memory & 8 kB SRAM, but could be used easily with other things, possibly SD alone is fast enough.
• look at this ESP32 cart. They have a lot of the same ideas.

Firmware

The firmware runs on the device to emulate ROM/RAM reading/writing data to a microSD card formatted FAT16/FAT32/ExFat. The firmware is meant to be compiled in Arduino IDE. If you open serial-monitor when it's running, you'll see some debugging output. On Arch Linux, I had to use arduino-PR-beta1.9-BUILD-117 for serial-monitor to work, due to some java error.

Files should all be in the root of the SDCard. The fRAM-size is 128K so you may hit limits if you have a ton of ROM files on the SD (limit should be around 8,737.) The file-list uses ROM-header-title, so if you have a bunch of the same ROM file-named differently, it will work, but in the ROM-list they will all have the same name. You can use this trick to have different copies of the same ROM with separate RAM files (like 1-per-song for nanoloop, for example.)

Software

A menu runs on the Gameboy to choose the current ROM/RAM. When a ROM is chosen, the gameboy reboots using that ROM/RAM.

To compile, run

make

in the software directory.

You can read more about it in software.

TODO

• Actually Implement MBC1
• Get SD-loading working (on boot load into RAM from SD while playing logo)
• Get menu working (get list of ROMs from firmware, on menu selection, set mem, load on reboot & clear mem)
• Implement MBC5
• Replace Nintendo logo with mine
• add extra IO-functionality, reading/writing to a specific memory location to turn on "I/O mode" and be able to interface with other peripherals
• Add support for sub-directories
• Create a modern cross-platform GBDK-focused full dev-env (use wine & docker to run stuff like GBTD.) Alternately, write some web-based tools around GBDK.js to allow sprite/map/sound editing.

License

• Hardware is licensed
• Firmware & Software is licensed

Thanks

• Lots of hardware/firmware ideas from here
• Ideas for menu ROM programming from gbdk_playground, gbdk-salvage, & GBSoundDemo