Chip8 Emulator

A super basic emulation of CHIP8. Nothin' fancy here.

Follow my work on wrapping this with WebAssembly to run in a browser here: chip8emu-wasm

<img src="https://github.com/dustinbowers/chip8emu/blob/master/screens/space-invaders.png" width="50%">

roms/ may or may not be available here https://github.com/jamesmcm/chip8go/tree/master/roms

Live Demo

For a WebAssembly / WebGL wrapped live demo see: https://dustinbowers.com/chip8

Usage

Install some stuff if you don't have SDL packages yet

brew install sdl2{,_image,_mixer,_ttf,_gfx} pkg-config

• Build: make
  • ./build/chip8-darwin [rom path]
• Run: make run

_{(Or live dangerously and run the pre-compiled darwin binary in build/)}

Input

| Key | Description | |-----|-----------------------------------------| | p | Pause emulator processing | | o | Resume emulator processing | | i | Inspect state of emulator (see console) |

Gamepad input: 16 keys, 0 to F (8, 4, 6, 2 are sometimes used for direction input)

Original gamepad

        1    2    3    C
        4    5    6    D
        7    8    9    E
        A    0    B    F

Keyboard mapping to the above ^

        1    2    3    4
        Q    W    E    R
        A    S    D    F
        Z    X    C    V

Architecture basics

Registers

• V0-VF: 16 * 1 byte

Note: VF is a "carry flag" register, used for carry / non-borrow / collision detection

Opcode table

There are 35 opcodes, each 2 bytes wide.

See: https://en.wikipedia.org/wiki/CHIP-8#Opcode_table

Memory map

+---------------+= 0xFFF (4095) End of Chip-8 RAM
|               |
|               |
|               |
|               |
|               |
| 0x200 to 0xFFF|
|     Chip-8    |
| Program / Data|
|     Space     |
|               |
|               |
|               |
+- - - - - - - -+= 0x600 (1536) Start of ETI 660 Chip-8 programs
|               |
|               |
|               |
+---------------+= 0x200 (512) Start of most Chip-8 programs
| 0x000 to 0x1FF|
| Reserved for  |
|  interpreter  |
+---------------+= 0x000 (0) Start of Chip-8 RAM

Stack

The original RCA 1802 version allocated 48 bytes for up to 12 levels of nesting. This implementation supports 16 levels

Timers (60hz)

• Delay timer (DT)
• Sound timer (ST)

TODO

• [x] File-path argument
• [x] Audio beep
• [x] Debug outputs
• [ ] RESET key

References

• https://en.wikipedia.org/wiki/CHIP-8
• http://devernay.free.fr/hacks/chip8/C8TECH10.HTM
• Chip8.pdf
• Special thanks to https://github.com/jamesmcm/chip8go/ for roms/ collection

Other screens

<img src="https://github.com/dustinbowers/chip8emu/blob/master/screens/pong.png" width="50%"> <img src="https://github.com/dustinbowers/chip8emu/blob/master/screens/ibm-logo.png" width="50%">