6502 Online Debugger

An interactive 6502 microprocessor emulator and debugger for the Nintendo Entertainment System (NES), providing educational insights into retro computing. Available at codeknight.dev.

Features

• Full 6502 CPU Emulation: Accurately emulates all official 6502 opcodes and addressing modes
• Interactive Debugging: Step-by-step execution with register and memory inspection
• Memory Visualization: Real-time view of memory contents and changes
• Cross-platform: Runs in any modern browser thanks to WebAssembly

Getting Started

The debugger is accessible online at codeknight.dev, but you can also run it locally or contribute to its development.

Prerequisites

• Docker and Docker Compose (for containerized development)
• Modern web browser with WebAssembly support

Local Setup

Quick Start

# Clone the repository
git clone https://github.com/MaxwellKnight/nes-emulator.git
cd nes-emulator

# Start development environment with web server
docker compose --profile dev up web-dev

# Build everything (native + WebAssembly)
docker compose run --rm dev

# Run tests
docker compose run --rm test

# Get an interactive shell
docker compose run --rm shell

Access the application at http://localhost:5173 during development or through the configured domain in production.

Local Development (without Docker)

For those who prefer developing without containers:

• Requirements:

• C++17 compatible compiler

• CMake 3.14 or newer

• Google Test framework

• Emscripten SDK (for WebAssembly compilation)

• Building:

mkdir build && cd build
  cmake ..
  make

Usage Guide

Basic Operation

• Navigate to codeknight.dev
• Use the "Load ROM" to upload a binary or paste 6502 compiled binary code

and click "Load Opcods"(online assembler masswerk.at)

• Use the debugger controls to:

• Step through code one instruction at a time

• Run code until a breakpoint

• Reset the emulator state

Memory and Register Inspection

• The register panel shows current values of A, X, Y, SP, and status flags
• Memory can be viewed and edited in the memory panel
• Watch specific memory addresses by adding them to the watch list

Architecture

The emulator is built with a focus on accuracy and educational value:

• Core 6502 CPU emulation written in C++
• WebAssembly compilation for browser execution
• Modern front-end interface built with HTML/CSS/JavaScript

License

This project is licensed under the GNU GPL v3 - see the LICENSE file for details.