GBC

A simple GameBoy and GameBoy Color emulator written in C.

This is a hobby project to try and write a simple emulator for the GameBoy, including its CPU, memory controller and display. It seems to work well enough with a number of games, but has not been extensively tested. If you want an actual practical GameBoy emulator you should use something different, there are plenty of mature emulators out there (e.g., Gambatte, BGB, VBA).

The emulator supports all opcodes of the GameBoy CPU (and passes the GameBoy tests from Blargg). It supports all areas of the GameBoy's MMU, including a number of different (on-cartridge) memory controllers (MBC-1, MBC-3 and MBC-5). It supports most of the LCD functionality (barring some sprite priority issues). A very hacky preliminary version of audio is implemented (supporting only some features of a single channel, 2). While audio is recognizable (e.g., the Tetris music), it's limited and its timing is off, making it rather unpleasant to listen to.

The emulator is relatively platform and architecture independent, and can be built using different front-ends: a standalone one using SDL2 and as a libretro core. libretro is a generic framework for emulators and runs on numerous systems. Using this frontend for this emulator allows it to even run on the SNES mini without modification (using hakchi2/Retroarch).

Building and usage

Any C compiler should work, but the emulator is currently tested with Clang and GCC. The standalone frontend depends on libreadline and libsdl2, available on Ubuntu with by installing libreadline-dev and libsdl2-dev. For the libretro core there are no dependencies for building, but using it requires a compatible frontend such as Retroarch.

Building and running the standalone frontend can be done as such:

$ make
$ ./main path/to/romfile

Running ./main -h shows all available options. Button mappings are as follows:

When the emulator detects unexpected behavior (e.g., accessing an unknown memory region), it will drop into a built-in debugger. This debugger can also be invoked manually using the b key. The debugger allows inspection of code, data and registers, can single-step the execution and set breakpoints, and can toggle debug-prints for instructions and memory accesses at run-time. For a list of commands, see the h command.

As a libretro core

To build just the libretro core, use the make libretro command, which will create koengb_libretro.so. By placing this shared library in the cores directory of a frontend such as Retroarch (~/.config/retroarch/cores) it can be selected from the interface.

Using the libretro core on the SNES mini

Note: There are much better and more mature emulators already available for the SNES mini.

Since the SNES mini (Super Nintendo Classic Mini) is simply an ARM chip running Linux, which can run Retroarch via hakchi2, we can run our libretro core on there as well simply by cross-compiling the code. This requires an ARM cross-compiler, which can be found on Ubuntu in the gcc-arm-linux-gnueabihf package. Then compiling can be done as such:

$ make clean  # To clean up any .o files created for the native architecture
$ make libretro CC=arm-linux-gnueabihf-gcc

Copy koengb_libretro.so to the SNES mini with hakchi2's FTP in /var/lib/hakchi/rootfs/etc/libretro/core. Create a folder in the games directory (/var/lib/hakchi/rootfs/usr/share/games/001), and modify the .desktop file in there to invoke Retroarch with this frontend (e.g., Exec=/bin/retroarch-clover koengb path/to/rom).

Currently the libretro support is limited, so exiting out of the emulator using the reset button, and managing states does not work yet.