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