Cowgod's Chip-8 Technical Reference | Hacker News Reader

Cowgod's Chip-8 Technical Reference

devernay.free.fr

49 pointstosh10 comments

For anyone looking to write a CHIP-8 emulator, Matt Mikolay's writeup is less ambiguous:

https://github.com/mattmikolay/chip-8/wiki/CHIP%E2%80%908-Te...

If you want to target the original Cosmac VIP behavior, corax89's test ROM is good:

https://github.com/corax89/chip8-test-rom

I can recommend Timendus test suite (which includes the one mentioned as well), as a more thorough set of tests and verification utilities: https://github.com/Timendus/chip8-test-suite

There are a lot of other useful references and tools worth mentioning, depending on how much hand-holding you want when implementing the emulator:

  - http://johnearnest.github.io/Octo/
  - https://laurencescotford.com/chip-8-on-the-cosmac-vip-index/
  - https://tobiasvl.github.io/blog/write-a-chip-8-emulator/

Additionally, note that there are lot of variants of the instruction set / system-specific quirks, which you probably don't want to entirely ignore in an implementation. In particular, the Cowgod's reference doesn't cover this fully (Matt Mikolay's is more thorough, but doesn't cover everything either).

Wow, wish I had seen Matt's writeup! I found Cowgod's guide to be ambiguous in several places (BCD and sprite loading especially) when I documented my emulator https://riv.dev/emulating-a-computer-part-1/

The VIPER newsletter for RCA VIP owners has quite a bit of the early CHIP-8 lore: https://github.com/mattmikolay/viper/ -- I wrote the "CHIP-8 Editor" in v4#1 and the "CHIP-8 Assember in BASIC" in Volume 6 issue 1.

It might be worth noting that there's still an active community writing new software for CHIP-8 (and its descendants) today. This October will be the ninth annual CHIP-8 game jam. It's a fun way to celebrate computing history and scratch that low-level programming itch: http://octojam.com

There's a gallery of previous submissions available here: https://johnearnest.github.io/chip8Archive/

I used this reference to write a CHIP-8 emulator in Z80 assembly a couple years back: https://github.com/mnurzia/chip8-ce

I enjoyed your commentry on the registers (HL, BC, DE), but you mention a lack of index-registers? Isn't that what IX and IY are for?

(You can do things like "ld a, (ix+3)", etc. I used those a lot when I recently wrote a text-based adventure game in Z80.)

Here is a Kotlin implementation of the emulator: https://github.com/cbeust/chip-8

and in particular, how each operand is implemented:

https://github.com/cbeust/chip-8/blob/master/src/main/kotlin...

I just used this reference to make my chip-8 python interpreter a few months back. As others have said, there are some ambiguities that caused a few headaches for me. Add to that some broken roms, and the process ended up a lot harder than it needed to be.

https://github.com/dreary-dugong/emu8

I’ve been using this as my reference for building a Chip-8 emulator in Zig, in order to learn Zig. Very useful.

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