CHIP-8 Interpreter

Introduction

A CHIP-8 interpreter written in Scala, using the Processing library for graphics.

Some context on CHIP-8:

CHIP-8 is a simple, interpreted, programming language which was first used on some do-it-yourself computer systems in the late 1970s and early 1980s. The COSMAC VIP, DREAM 6800, and ETI 660 computers are a few examples. These computers typically were designed to use a television as a display, had between 1 and 4K of RAM, and used a 16-key hexadecimal keypad for input. The interpreter took up only 512 bytes of memory, and programs, which were entered into the computer in hexadecimal, were even smaller.

(http://devernay.free.fr/hacks/chip8/C8TECH10.HTM#1.0)

Usage

Run the interpreter

1. Update the gradle.properties file
   • Either:
     • delete it, and use Java 8
     • set it to your JAVA_HOME
   • It is currently set to my own (macOS) Java 8 installation
   • This is needed because I cannot use Java 8 as my main Java version, due to other applications needing newer versions.
2. If wanted, modify the quirks.properties file to a different ROM.
   • by default, it is set to roms/3-corax+.ch8, which is an extensive test rom
3. Run the run gradle task, or, as in Tetris, click on the green "play button" in ChipVM.scala inside of IntelliJ

I based my implementation mostly on the testing ROMs, the demo (games, etc.) roms were not tested much.

Controls

The keypad is mapped to the following keys:

1234
QWER
ASDF
ZXCV

ROMs

Various Testing Roms

These are various testing roms that I found online and used to test the interpreter. Many games might still be buggy, but this is because they might depend on specific quirks and behaviours I did not implement.

• roms/1-chip8-logo.ch8
  • Displays a CHIP-8 testing suite logo
• roms/2-ibm-logo.ch8
  • Displays the IBM logo
• roms/3-corax+.ch8
  • Tests many instructions
• roms/4-flags.ch8
  • Tests if flags are properly set (VF)
• roms/5-quirks.ch8
  • quirks that the test suite considers important to follow (might cause bugs in some roms)
• roms/6-keypad.ch8
  • tests keypad
• roms/7-fontTest.ch8
  • displays a character from the font set
• roms/7-fontTest-Double.ch8
  • displays a character twice, as to make the display clear again

Demos

These are demos that I found online, I did not make them myself, nor did I test them extensively.

• roms/sir.ch8 - Triangle
• roms/maze.ch8 - Randomly generated maze
• roms/pong.ch8 - Pong
  • 1 for P1 Up
  • Q for P1 Down
  • 4 for P2 Up
  • R for P2 Down
• roms/br8kout.ch8 - Breakout
  • A for Left
  • D for Right
• roms/tetris.ch8 - Tetris
  • W for Left
  • E for Right
  • Q for Rotate
• roms/buggy-RoShamBo.ch8 - RoShamBo/RPS
  • Known bug: Display also is a bit wonky: the indicated letters do not actually show that RPS move, and it does not always reset properly. It might rely on quirks or extended behaviours.
  • Z for Rock
  • X for Paper
  • C for Scissors
• roms/war.ch8 - Press F to pay respects
  • V to pay respects (V is placed on the location of the original keypad's F)

Tests

This interpreter passes pretty much all tests across corax+, flags, quirks and keypad:

3-corax+.ch8

4-flags.ch8

5-quirks.ch8

6-keypad.ch8

Process and Notes

I implemented CHIP-8 as correctly and extensively as I could, yet limitations are still present:

• All test roms work
  • 5-quirks.ch8: the display being "low" is the only complaint, but seemingly it is not a bug.
• Trying to use Minim for sound was a horrible experience, and I was forced to remove it from my interpreter as I feared it would make it crash in unexpected ways.
  • It bugged out saying files did not exist when they did
  • The Oscillator (for custom square wave generation) was not working as well as needed: it did not turn on and off quirkly enough
    • at times, it slowed down the program to a crawl
• Some roms are buggy (e.g. RPS), but they work well enough to demonstrate the interpreter's full functionality.
  • RPS has a bug where dual input might happen, I fear this might have to do with Processing and Java's AWT.

Note that there was a best effort to make the interpreter immutable.