Project 14: Game Boy Emulator (Retro Hardware Simulation)

A complete Game Boy emulator that runs real cartridge ROMs—emulating the CPU, memory, graphics (PPU), and sound.

Quick Reference

Attribute Value
Primary Language Rust
Alternative Languages C++, C
Difficulty Level 4: Expert
Time Estimate 1-2 months
Knowledge Area Emulation / CPU Architecture / Graphics
Tooling SDL2 or minifb for graphics
Prerequisites Projects 1-4 completed, understanding of binary/hex

What You Will Build

A complete Game Boy emulator that runs real cartridge ROMs—emulating the CPU, memory, graphics (PPU), and sound.

Why It Matters

This project builds core skills that appear repeatedly in real-world systems and tooling.

Core Challenges

  • Implementing the LR35902 CPU instruction set → maps to pattern matching and state machines
  • Cycle-accurate timing → maps to precise scheduling and accounting
  • Graphics scanline rendering → maps to low-level graphics programming
  • Memory banking and cartridge handling → maps to memory-mapped I/O

Key Concepts

  • Z80-like instruction set: “Game Boy Coding Adventure” - Dagois
  • PPU rendering: Pan Docs (gbdev.io)
  • Cycle timing: “Writing a Game Boy Emulator” - blog series by various authors
  • Graphics with SDL2: “Rust Game Development” or minifb documentation

Real-World Outcome

┌────────────────────────────────────────────────┐
│                                                │
│     ┌──────────────────────────────────┐       │
│     │                                  │       │
│     │   ████  TETRIS  ████             │       │
│     │                                  │       │
│     │      ▓▓                          │       │
│     │      ▓▓                          │       │
│     │    ▓▓▓▓▓▓                        │       │
│     │                                  │       │
│     │  ████████                        │       │
│     │  ████████                        │       │
│     │  ████████████                    │       │
│     │                                  │       │
│     │  SCORE: 1337    LEVEL: 5         │       │
│     │                                  │       │
│     └──────────────────────────────────┘       │
│                                                │
│     [A] [B] [SELECT] [START]                   │
│         [↑]                                    │
│       [←] [→]                                  │
│         [↓]                                    │
│                                                │
└────────────────────────────────────────────────┘

$ cargo run --release tetris.gb
🎮 RustBoy Emulator
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
ROM: tetris.gb
Cartridge Type: ROM ONLY
Running at 59.73 FPS (4.19 MHz CPU)

Controls: Arrow keys, Z=A, X=B, Enter=Start

Implementation Guide

  1. Reproduce the simplest happy-path scenario.
  2. Build the smallest working version of the core feature.
  3. Add input validation and error handling.
  4. Add instrumentation/logging to confirm behavior.
  5. Refactor into clean modules with tests.

Milestones

  • Milestone 1: Minimal working program that runs end-to-end.
  • Milestone 2: Correct outputs for typical inputs.
  • Milestone 3: Robust handling of edge cases.
  • Milestone 4: Clean structure and documented usage.

Validation Checklist

  • Output matches the real-world outcome example
  • Handles invalid inputs safely
  • Provides clear errors and exit codes
  • Repeatable results across runs

References

  • Main guide: LEARN_RUST_DEEP_DIVE.md
  • “Game Boy Coding Adventure” by Maximilien Dagois + Pan Docs