chipgenics

Quarantine day 22: "I think I'm gonna write a hardware emulator"

chipgenics is my homemade implementation of a CHIP-8 Virtual Machine running 100% on Javascript. It can be used as the core code for web, mobile or even Node.JS applications. A live demo is available on chipgenics.site.

What is CHIP-8?

CHIP-8 is an interpreted programming language developed by Joseph Weisbecker during the 1970's. A lot of famous games have their version for CHIP-8, such as Space Invaders, Tetris and others.

Screenshot of Space Invaders as developed by David Winter running on chipgenics

The architecture

CHIP-8 was designed to have a very simple implementation. Its CPU had 16 one-byte registers, apart from a special one used to store memory addresses. Most implementations had a memory of 4096 positions. The processor also had a stack which allowed up to eight recursive subroutine calls. This project implements the CHIP-8 in its original architecture, component by component.

Instruction Set

CHIP-8 had a instruction set composed by 48 instructions, including arithmetic and boolean operations, logical jumps, subroutines and a special instruction to draw on the screen. The complete CHIP-8 instruction set can be found here.

Stop talking, show me the code

After cloning this project and installing the dependencies, you can use the emulator core code requiring the main file under src/chip8.

const Chip8 = require('src/chip8')

const program = [
  0x00e0, // Clears the screen
  0x6102, // v1 = 02
  0x6202, // v2 = 02
  0xa00a, // sets I to 0x000a (position of the sprite for `2`)

  0xd125  // draws the number "2" on the screen
]

const chip8 = new Chip8({
  memory: {
    program
  }
}).start()

console.log(chip8.display.render())
// => this will log the rendered screen on the output

Alternatively you can also load a program directly from a ROM using the loadProgram method from the Chip8.Memory class.

Known issues

• The sound timer is still not implemented.
• There is an issue in at least one implemented instruction. You can tell it by playing Space Invaders firing a bullet, you will see that some unexpected things happen then. I will totally pay you a beer if you can find it :)