GBA Emulator Project (C++20 / SDL2)

A high-performance Game Boy Advance emulator written in modern C++ (C++20), utilizing SDL2 for rendering and input. This project implements a cycle-accurate ARM7TDMI CPU core, supporting both ARM and Thumb instruction sets, a functional PPU for Mode 3/4/5 rendering, and an MMU with mirroring support.

Features

ARM7TDMI Core

• Full Instruction Set Support:
  • Implements all ARM v4T instructions (Data Processing, Multiply/Long Multiply, LDR/STR, LDM/STM, Swap, Branches, PSR Transfer).
  • Implements all Thumb instructions (Formats 1-19).
• Accurate Pipeline & Timing:
  • Simulates the 3-stage pipeline (Fetch-Decode-Execute) behavior (PC = Instruction Address + 8/4).
  • Cycle counting for accurate timing emulation.
• Register Banking:
  • Complete implementation of banked registers for all CPU modes (User, System, FIQ, IRQ, Supervisor, Abort, Undefined).
• Verified Accuracy:
  • Passed 100% of tests in gba-tests/arm/arm.gba (532 tests).
  • Passed 100% of tests in gba-tests/thumb/thumb.gba.

Memory Management Unit (MMU)

• Memory Map Implementation:
  • BIOS (0x00)
  • EWRAM (0x02)
  • IWRAM (0x03)
  • I/O Registers (0x04)
  • Palette RAM (0x05)
  • VRAM (0x06) with correct mirroring behavior.
  • OAM (0x07)
  • Game Pak ROM (0x08 - 0x0D)
  • SRAM (0x0E)
• Wait State Handling:
  • Region-specific cycle costs (e.g., fast IWRAM vs slow ROM).

Picture Processing Unit (PPU)

• Bitmap Modes Supported:
  • Mode 3: 240x160 Direct Color (15-bit).
  • Mode 4: 240x160 Palette Index (8-bit) with Page Flipping.
  • Mode 5: 160x128 Direct Color (15-bit) with Page Flipping.
• Rendering Pipeline:
  • Scanline-based rendering (HDRAW/HBLANK/VDRAW/VBLANK timings).
  • Accurate VCOUNT and DISPSTAT status updates.

Build Instructions

Prerequisites

• CMake (3.10+)
• C++ Compiler with C++20 support (MSVC, GCC, Clang).
• SDL2 (Fetched automatically via CMake FetchContent).

Building

1. Clone the repository.
2. Create a build directory:

   mkdir build
   cd build

3. Configure and build:

   cmake .. -DCMAKE_BUILD_TYPE=Release
   cmake --build . --config Release

Running the Emulator

Run the executable with a path to a GBA ROM file:

./Release/GBA_Emulator.exe path/to/rom.gba

Running Tests

The project includes a headless test runner for verifying CPU correctness against gba-tests.

./Release/GBA_Tests.exe path/to/test_rom.gba

Architecture

• src/: Source code files.
  • GBA.cpp/h: System coordinator (Top-level class).
  • CPU.cpp/h: ARM7TDMI implementation (Registers, Decoder, ALU).
  • MMU.cpp/h: Memory map, read/write logic, DMA hooks.
  • PPU.cpp/h: Graphics rendering engine.
  • Utils.h: Common bit-twiddling and helper functions.
  • main.cpp: SDL2 entry point, event loop, and frame timing.
• tests/: Test suite integration.

License

This project is open-source.