Imran Nazar writes about web development and retrocomputing, including a Game Boy emulator tutorial in JavaScript and Commodore 64 projects.
Commenters recommend his Game Boy emulation series as an excellent writeup, and one is porting it to TypeScript to learn emulator writing.
Sure!
This walkthrough[1] writing a Gameboy emulator in Javascript was very helpful in seeing how an emulator should be structured. -- Though the full source is available: the actual tutorial is more of a guideline that introduces you to the hardware and structure of the emulator. It often shows code-snippets instead of working code.
The Gameboy CPU Manual[2] and OP code chart[3] have been invaluable tools. In my experience: I spent most of my time flipping between the opcode chart and my CPU implementation.
As a tip: lots of the CPU instructions do the same thing w/ different register pairs. There is huge potential for code reuse here. In Rust I achieved it with macros, though.
Lastly: the "Pan Docs"[4] are more or less the same thing as the CPU Manual, but in a slightly more readable format.
Also there[5] are some test ROMs[6] that you can use for debugging.
I'm trying to find a good way to verify their results using Rust's unit testing.
`opus5.gb`[6] is a nice way to test the graphics subsystem; it's also a good "first ROM" to run because it has no additional ROM or RAM in the cartridge. In other-words: you don't need to implement the memory bank controllers to get it working.
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And a little bit of friendly advice: _always_ keep debugging in the back of your mind. I usually resort to "printf debugging" but that really doesn't work inside a loop that's supposed to be ticking at 4.19MHz! :)
I accidentally filled up my disk once already; I forgot I had redirected…
If you're interested in making a GB emulator here are a few resources that helped me when I did just that a few years ago:
- An intro to making a GB emulator in JS (it doesn't matter if you don't plan on using JS, it still explains the basic concepts pretty well): http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-The-CPU
- Opcode map (note that the GB CPU is not a stock Z80, it has different timings, different registers, different flags and different opcodes, do not use stock Z80 docs as a reference lest you end up with broken CPU emulation): http://www.pastraiser.com/cpu/gameboy/gameboy_opcodes.html
- The GameBoy programming manual: http://www.romhacking.net/documents/544/
- Accuracy test ROMs, very useful to make sure your timings are ok and you emulate various quirks of the hardware: http://tasvideos.org/EmulatorResources/GBAccuracyTests.html
Also note that even if you focus on making an original (DMG) GameBoy emulator you should be able to add GameBoy Color support later without too much difficulty, it's a fairly straightforward evolution of the original hardware.
Porting http://imrannazar.com/GameBoy-Emulation-in-JavaScript to Typescript as a way to learn about how to write an emulator, as well as taking advantage of newer JavaScript APIs (e.g. requestAnimationFrame, ArrayBuffer etc) that were not available when this series of articles was written in 2010.
We had a gameboy as a kid, but the ZX Spectrum (also Z80 CPU-based) meant more to me so hope to take what I learn from the great articles from imrannazar.com and apply to writing a ZX Speccy emulator (the gameboy had dedicated-hardware for sprites etc so not everything will be transferable).
Yes both gameboy & spectrum emulators in javascript have been done already, but this is just for personal learning/fun/itch-scratching. It has been quite instructive both from a remembering-fundamental-cs-classes/how-computers-really-work perspective, as well as modern javascript
There used to be a demo floating around where someone had hacked this together with the firefox nightlies' support for the orientation sensor that allowed to your drive the kart by tilting your device. It worked for macbook as well as smartphones. Unfortunately the page is now down :( http://dougt.org/random/orientationdemo/index.xhtml
In lieu of that, I present to you something much more interesting: A complete step-by-step guide to writing your own fully functioning gameboy emulator in javascript+html5 (without sound.) It's really easy to follow even if you know nothing at all about emulators.
http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-The-CPU
It was not for no reason. When adding a screw hole in the motherboard so it could be mounted in the case, they accidentally removed the high speed wire, dooming the C64 to the same slow data speed of the VIC-20 with it's faulty VIA.
The C64 data speed actually ended up being even slower than the VIC-20. You can read the full detailed here: https://imrannazar.com/articles/commodore-1541
This is some incredible work. There's a few ports out there I've tried, but this is by far the most performant yet. Definitely interested to see how further it's taken.
I'm also interested to see where the author learned about the inner workings of the Gameboy (i.e, if Nazar's work had any influence: http://imrannazar.com/GameBoy-Emulation-in-JavaScript:-The-CPU )