NES Snake

A classic Snake game written in 6502 assembly for the Nintendo Entertainment System.

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Background

This project stems from my exploration of NES development and emulation back in 2020. What started as curiosity about how games worked on the 8-bit era hardware turned into a deep dive into 6502 assembly, PPU rendering, and the elegant constraints that shaped an entire generation of games.

This repository is documented and shared for anyone who shares that same curiosity — whether you're learning assembly for the first time or revisiting the fundamentals of game development on limited hardware.

How It Works

Architecture Overview

The NES runs on a MOS 6502 CPU (modified as 2A03) at 1.79 MHz with just 2KB of RAM. Graphics are handled by the Picture Processing Unit (PPU), which renders tiles from pattern tables stored in CHR ROM.

This game uses:

• Nametable rendering for the playfield (32x30 tiles)
• Background tiles for snake, food, and walls (no sprites)
• Controller polling via memory-mapped I/O at $4016
• NMI (Non-Maskable Interrupt) driven game loop synced to 60Hz VBLANK

Memory Map

Address	Purpose
$0000-$00FF	Zero Page (fast access variables)
$0100-$01FF	Stack
$0200-$07FF	RAM (snake position arrays)
$2000-$2007	PPU registers
$4016	Controller input
$8000-$FFFF	PRG ROM (game code)

Game Logic

• Snake positions stored in X/Y coordinate arrays (max 64 segments)
• Movement updates every 8 frames (~7.5 tiles/second)
• Collision detection checks walls and self-intersection
• Food spawns using pseudo-random generation from frame counter and snake position

Building

Prerequisites

You'll need the cc65 toolchain, which includes:

• ca65 — 6502 macro assembler
• ld65 — linker

macOS (Homebrew):

brew install cc65

Ubuntu/Debian:

sudo apt install cc65

Windows:

Download from cc65.github.io or use the Windows snapshot builds.

Compile

make

This produces snake.nes — a standard iNES ROM file.

To clean build artifacts:

make clean

Run

Load snake.nes in any NES emulator:

Platform	Recommended Emulators
macOS	Nestopia UE, OpenEmu
Windows	Mesen, FCEUX
Linux	Nestopia UE, Mesen
Web	JSNES

macOS with Homebrew Nestopia:

nestopia snake.nes

Controls

Button	Action
D-Pad	Change direction
Start	Restart (after game over)

Technical Specifications

Property	Value
Mapper	NROM (Mapper 0)
PRG ROM	32 KB
CHR ROM	8 KB
Mirroring	Vertical
Battery	No

Project Structure

.
├── Makefile      # Build configuration
├── nes.cfg       # Memory layout for linker
├── snake.asm     # Game source code
└── snake.nes     # Compiled ROM

Learning Resources

If you're interested in NES development, these resources were invaluable:

Tutorials & Guides

• NES ASM Tutorial (Patater) — Beginner-friendly introduction to NES assembly
• Nerdy Nights — Comprehensive weekly tutorial series
• NESdev Wiki — The definitive reference for NES hardware and programming

Architecture & Hardware

• 6502 Instruction Set — Complete opcode reference
• Easy 6502 — Interactive 6502 tutorial in the browser
• NES Rendering Overview — How the PPU draws frames

Tools

• cc65 — C compiler and assembler suite for 6502
• FCEUX Debugger — Step through code, inspect memory
• YY-CHR — Tile/sprite editor for NES graphics

Community

• NESdev Forums — Active community of homebrew developers
• r/nesdev — Reddit community for NES development

License

This project is released into the public domain. Use it to learn, modify, and build your own NES games.

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Built with curiosity and a hex editor.