# gameboy-rust

Game Boy family emulation in Rust, written from scratch.
The Game Boy Advance (GBA) is the first and currently only system.

**This cannot run Pokémon Emerald or other commercial games yet.**
It is an emulator foundation: an ARM7TDMI interpreter, memory bus, timers, DMA, Mode 0–5 video, and an original BIOS replacement.
The included demos run original ARM test programs through the emulated hardware.
Raw ROM files can run in terminal sessions or a window with keyboard input. Audio and saves are not implemented.
A [pinned Pong homebrew](docs/public-pong.md) passes scripted menu, ball-motion, and paddle-input checks.

## Layout

| Crate | Purpose |
| --- | --- |
| `crates/gba-core` | Platform-independent GBA emulator. No external Rust dependencies. |
| `crates/gba-demos` | Original test programs that drive the core. |
| `crates/desktop` | Native window frontend on minifb. Builds the `gameboy-rust` executable. |

## Quick start

macOS on Apple Silicon is the verified platform. Install Nix (with flakes) and direnv, then:

```sh
direnv allow .
direnv exec . cargo run --locked --release -- --tile-demo
direnv exec . cargo test --locked
```

Arrows scroll, Q rotates, W zooms, Z flips, X changes priority, Enter resets, and Escape exits.
Run `direnv exec . cargo run --locked -- --help` to list all modes.
For original ROM files, use `--rom path/to/original.gba --window`, or `--steps 100000` instead of `--window` for terminal diagnostics.
See [cartridge loading](docs/hardware/cartridge.md) for limits and report meanings.
Use `--test-suite suite.json` for [repeatable headless ROM assertions](docs/rom-tests.md).

## Documentation

| Document | Contents |
| --- | --- |
| [docs/status.md](docs/status.md) | What works today, deliberate limits, and next steps |
| [docs/usability-roadmap.md](docs/usability-roadmap.md) | General GBA usability criteria and feature priorities |
| [docs/demos.md](docs/demos.md) | Every demo, its command, and its controls |
| [docs/development.md](docs/development.md) | Nix, direnv, and macOS build notes |
| [docs/testing.md](docs/testing.md) | Validation commands and what the test suites cover |
| [docs/rom-tests.md](docs/rom-tests.md) | Headless ROM suites, completion checks, assertions, and JSON reports |
| [docs/jev-debugging.md](docs/jev-debugging.md) | Optional `/jev-gb-debug` workflow, evidence review, and local evaluation records |
| [docs/public-arm-tests.md](docs/public-arm-tests.md) | Pinned public ARM test, preparation command, results, and limits |
| [docs/public-thumb-tests.md](docs/public-thumb-tests.md) | Pinned public Thumb test, result protocol, and compatibility baseline |
| [docs/public-memory-tests.md](docs/public-memory-tests.md) | Pinned public memory test, results, and video-byte coverage limits |
| [docs/public-bios-tests.md](docs/public-bios-tests.md) | Pinned BIOS read-protection result and firmware limits |
| [docs/public-pong.md](docs/public-pong.md) | Playable homebrew setup, scripted gameplay baseline, and limits |
| [docs/architecture.md](docs/architecture.md) | Crate boundaries and a file-by-file map |
| [docs/hardware/cpu.md](docs/hardware/cpu.md) | ARM/Thumb execution rules, modes, exceptions, and timing |
| [docs/hardware/cartridge.md](docs/hardware/cartridge.md) | ROM loading, window/input controls, original ROM generator, and diagnostics |
| [docs/hardware/save-states.md](docs/hardware/save-states.md) | Whole-machine save states, F5/F9 hotkeys, format, and limits |
| [docs/hardware/bios.md](docs/hardware/bios.md) | The original BIOS replacement and each supported service |
| [docs/hardware/timers-irq.md](docs/hardware/timers-irq.md) | Timers, interrupt registers, HALT/STOP, and power control |
| [docs/hardware/dma.md](docs/hardware/dma.md) | DMA channels, triggers, and timing |
| [docs/hardware/audio.md](docs/hardware/audio.md) | Sound devices, stereo capture, optional Darwin output, and limits |
| [docs/hardware/serial.md](docs/hardware/serial.md) | Disconnected serial initialization and transfer limits |
| [docs/hardware/display-timing.md](docs/hardware/display-timing.md) | Display clock, status, IRQs, and scanline capture |
| [docs/hardware/video.md](docs/hardware/video.md) | Backgrounds, sprites, mosaic, windows, color effects, and input |
| [docs/references.md](docs/references.md) | External hardware references and emulator sources consulted |

Coding agents should start with [AGENTS.md](AGENTS.md).

## Legal

All demo content and the BIOS replacement are original. No Nintendo code or assets are included.
Only use game ROMs that you may lawfully use. Do not commit game ROMs, BIOS files, or game assets.