Building a CHIP-8 Emulator in Rust

Some projects teach you a programming language. Others teach you how computers work at a low level. This one does both at the same time.

We are going to build a CHIP-8 emulator from scratch. CHIP-8 is a small virtual machine designed in the 1970s for programming games on early microcomputers. It is the classic first emulator project — small enough to finish, complex enough to be interesting, and well-documented enough that you can focus on learning rather than archaeology.

By the end, you will have a program that runs real CHIP-8 games. Along the way, you will learn Rust from the ground up, understand how a CPU executes instructions, and see exactly what happens between "program starts" and "pixels appear on screen."

What is CHIP-8?

CHIP-8 is not a real chip — it is a specification for a virtual machine. Programs written for CHIP-8 do not run on hardware directly; they run on an interpreter. In the 1970s, that interpreter ran on real machines like the COSMAC VIP. Today, we write the interpreter ourselves.

The specification is intentionally minimal:

  • 4 KB of memory — the entire address space fits in what modern computers would call a rounding error
  • 16 registers — each holding one byte (0–255)
  • 35 opcodes — the complete instruction set fits on one page
  • 64×32 pixel display — monochrome, no color, no gradients
  • 16-key hexadecimal keypad — the input device

This minimalism is what makes CHIP-8 perfect for learning. There are no device drivers, no memory management, no privilege levels. Just a loop: fetch instruction, decode it, execute it, repeat.

Why Rust?

Rust is a systems programming language that gives you the control of C with the safety guarantees of a modern language. It will not let you read uninitialized memory. It will not let you have two mutable references to the same data at the same time. These constraints feel restrictive at first — then you start to appreciate that the compiler is catching entire categories of bugs before your program ever runs.

Emulators are a natural fit for Rust. They deal with raw bytes, bit manipulation, and fixed-size data structures — exactly the kind of low-level work where Rust shines. And because the emulator is small, you will encounter Rust's most important concepts without being overwhelmed by framework complexity.

How this book is structured

Each chapter introduces a new concept exactly when the implementation needs it. We do not front-load theory. When we need to understand bitwise operations, it is because we are about to decode an opcode. When we need to understand closures, it is because we ran into a compiler error while building the render loop.

The book is divided into eight parts:

  1. Getting Started — setting up the project with Cargo
  2. The CPU — modeling the processor as a Rust struct
  3. Memory — the 4KB address space and how to organize code
  4. Fetch, Decode, Execute — the CPU loop and our first opcodes
  5. Data and Arithmetic Opcodes — loading values, doing math
  6. Control Flow Opcodes — jumps, calls, conditions, and randomness
  7. The Display — the framebuffer and drawing sprites
  8. The Main Loop — opening a window and making it run

Every chapter builds on the one before it. The source code for each stage is tested — when something works, we know it works.

Prerequisites

You need Rust installed. The easiest way is via rustup:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

No prior Rust knowledge is required. Basic familiarity with any programming language (variables, loops, functions) is enough to follow along.