99z / halken

A Game Boy emulator written in Go

halken

Video games are meant to be just one thing. Fun. Fun for everyone.

Satoru Iwata

Halken is a Game Boy emulator written in Go being developed during my time at the Recurse Center. The name is one used by HAL Laboratories for a time. HAL was the first company where Satoru Iwata was a video game programmer.

I intend to have lots of comments as well as a document regarding the process. Once I am happy with 32KB games generally working I'll be cleaning the code and writing documentation for others who want to tackle the same project.

Known working games

Usage: halken /path/to/rom

1. Tetris
2. Dr. Mario
3. Flipull
4. World Bowling
5. Minesweeper
6. Motorcross Maniacs
7. Hyper Lode Runner
8. Battlecity

Known bugs

• LCD STAT interrupt is only partially correct - need to make sure all cases are covered
  • Breaks certain games like Game of Harmony, which gets weird graphics due to it not firing when it should
• Sprite color palettes besides default are unimplemented
• 8x16 sprites aren't drawn properly, get cut off

TODO

1. Implement CPU opcodes
   • Non-CB opcodes implemented
   • Write dispatch loop
   • Use blargg's test output to fix instructions
     • 01 - special
     • 02 - interrupts
     • 03 - op sp,hl
     • 04 - op r,imm
     • 05 - op rp
     • 06 - ld r,r
     • 07 - jr,jp,call,ret,rst
     • 08 - misc instrs
     • 09 - op r,r
     • 10 - bit ops
     • 11 - op a,(hl)
2. Implement memory
3. Test GB bootstrap ROM
4. Draw tiles
5. Draw background
6. Graphics loop
7. Interrupts
   • VBlank
   • LCD
   • Timer
   • Serial
   • Joypad
8. Timer
9. Refactor (direct memory access vs. abstractions), lower LOC, comment
10. Document process for learners