README.md

GoBoy

GoBoy is a multi-platform Nintendo GameBoy and GameBoy Color emulator written in go. This emulator was primarily built as a development exercise, and while still work in progress it should run the majority of GB games, and some CGB games. There is also experimental sound and colour support implemented.

The program includes debugging functions which make it useful for understanding how the emulator is working or for building one yourself, such as a method for printing out opcodes and register values to the console at each step. Turning these on will slow down the emulation.

Installation

go get github.com/Humpheh/goboy

The program has been tested on MacOS and Windows 10, and is likely to work on Linux. Building on Windows 10 requires MinGW.

GoBoy uses the go library pixel for control binding and graphics rendering, which requires OpenGL. Instructions on installing them can be found on the pixels readme.

Usage

goboy -sound -cgb -rom zelda.gb

Controls: ← ↑ ↓ → Z X Enter Backspace

The colour palette can be cycled with = (in DMG mode), and the game can be made fullscreen with F.

Other options:

  -cgb
        set to enable cgb mode
  -cpuprofile string
        write cpu profile to file
  -disableVsync
        set to disable vsync
  -load string
        location of save state to load (experimental)
  -rom string
        location of rom file (required)
  -sound
        set to enable sound emulation (experimental)
  -stepthrough
        step through opcodes (debugging)
  -unlocked
        if to unlock the cpu speed (debugging)

Debugging

There are a few keyboard shortcuts useful for debugging:

Q - force toggle background
W - force toggle sprites
A - print gb background palette data (cgb)
S - print sprite palette data (cgb)
D - print background map to log
E - toggle opcode printing to console (will slow down execution)
7,8,9,0 - toggle sound channels 1 through 4.

Saving

If the loaded rom supports a battery a <rom-name>.sav (e.g. zelda.gb.sav) file will be created next to the loaded rom containing a dump of the RAM from the cartridge. A loop in the program will update this save file every second while the game is running.

Testing

GoBoy currently passes all of the tests in Blargg's cpu_instrs and instr_timing test roms.

These roms are included in the source code along with a test to check the output is as expected (instructions_test.go and timing_test.go). These tests are also run on each commit.

Contributing

Feel free to open pull requests to this project or play around if you're interested!

Known Bugs

• Sprite Z-drawing
• Sprites near edge of screen not drawing
• Top half of sprite disappearing off top of screen
• Small sprites row glitch
• Many CGB bugs
• BG tile window offset issue - visible on Pokemon Red splash screen - possibly mistimed interrupt?

TODO List

• MBC3 banking support
• GameBoy Color support (partial)
• Rewrite APU emulation
• MBC3 clock support
• Complete CGB emulation
• Icon
• White screen when off
• Speed up CPU
• Resizable window
• Some kind of nice UI
• MBC4-7 support (?)
• More colour palettes
• STOP opcode behaviour
• Blargg's test ROMs

Resources

A large variety of resources were used to understand and test the GameBoy hardware. Some of these include:

• http://www.codeslinger.co.uk/pages/projects/gameboy/files/GB.pdf
• https://github.com/retrio/gb-test-roms
• http://www.codeslinger.co.uk/pages/projects/gameboy/beginning.html
• http://bgb.bircd.org/ - invaluable for debugging
• https://github.com/AntonioND/giibiiadvance/tree/master/docs
• https://github.com/trekawek/coffee-gb