yagb's Introduction

Yet Another GameBoy Emulator

What?

Emulates the GameBoy (monochrome only) pretty decently. All major features are implemented and plenty of games and demoscene releases run.

Supported features

GameBoy CPU core (Z80-like)
LCD controller
- Tiled primary background & the window (a secondary BG layer)
- Background scrolling
- IRQs for VBlank & raster position
- Sprites & sprite DMA
Sound
- 2 square wave channels
- Wave channel
- Noise channel
Joypad (+ IRQ)
Timer (+ IRQ)
Dummy serial port (+ IRQ)
- Some weird games use the transmit IRQ for timing purposes...
MMC memory mappers + battery-backed save RAM
VRAM debug viewer
Save states

What's missing

Frequency sweep on the 1st square wave channel
Real Time Clock in the MMC3
Non-Nintendo mappers

And of course, plenty of bugs/emulation inaccuracies, see GitHub issues for some details.

Compiling & running

You'll need a C++11 compiler, Qt5 headers, and an OpenGL-capable machine. Compile with make. Run with:

./yagb [-t] path/to/rom/file.gb

Use -t to print a trace of all executed instructions and memory accesses made by the CPU or sprite DMA. For example:

[mem rd (CPU)] 0x0100: 00
[insn 00332/153/00000404] 0x0100:       00 => NOP                              A: 0x01 | BC: 0x0013 | DE: 0x00d8 | HL: 0x014d | SP: 0xfffe | Flags: Z-HC. | Cycles: 4
[mem rd (CPU)] 0x0101: c3
[mem rd (CPU)] 0x0102: 50
[mem rd (CPU)] 0x0103: 01
[insn 00332/153/00000408] 0x0101: C3 50 01 => JP 0x0150                        A: 0x01 | BC: 0x0013 | DE: 0x00d8 | HL: 0x014d | SP: 0xfffe | Flags: Z-HC. | Cycles: 16
[mem rd (CPU)] 0x0150: f3
[insn 00332/153/00000424] 0x0150:       F3 => DI                               A: 0x01 | BC: 0x0013 | DE: 0x00d8 | HL: 0x014d | SP: 0xfffe | Flags: Z-HC. | Cycles: 4

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yagb's Issues

Demo-specific emulation issues:

20y: side-to-side scanline moving in first part isn't visible (intra-scanline timing?)
gejmboj: twisting part before the dog part is broken (intra-scanline timing?)
jml-we: crashes on gambatte?
mc-mrder: screen stays black & tileram stops updating very soon, music keeps playing ok
oh: side-to-side scanline moving in the last part isn't visible (intra-scanline timing?)
qt-tsu: gambatte displays some screen garbage in plasma scene
yup-demonblood: arrow doesn't move in arrow scene

Game-specific emulation bugs

Alleyway: raster effects are off by one scanline
Super Mario Land 2: won't go past title screen
- Most likely root cause: vblank irq gets pending while screen is off => ~~not expected by game at (0x0259)~~
  - Not a problem at (0x0259). But:
    - at (0x2BBF): ROM bank is switched to 0x1b, also saved to (0xa24e)
    - at (0x2BD3): ROM bank is switched to 0x0c, but (0xa24e) is NOT updated
    - VBlank IRQ occurs (LCD is off)
    - at (0x01D6): IRQ handler restores bank from (0xa24e) to 0x1b, which is incorrect
Pokemon: Wave music notes sound crappy
Sprite renderer needs rewrite
- Metroid 2, Zelda, Super Mario Land 2: asserts in sprite code
- Pokemon: incorrect priority in title screen
Multiple SaveRAM banks broken

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