6 ms·

An emulator is still on my "bucket list as an engineer." I feel like it's a hurdle I still haven't crossed and I'm reasonably certain I could make one. I have

An emulator is still on my "bucket list as an engineer." I feel like it's a hurdle I still haven't crossed and I'm reasonably certain I could make one. I have some free time this weekend...I might take this repo and port it over to clojure to get the hang of things.

laputan_machine 5y ago
The first emulator I wrote was for a virtual machine called the CHIP-8. I used CowGod's reference, it was a fun experience! http://devernay.free.fr/hacks/chip8/C8TECH10.HTM#2.1 http://devernay.free.fr/hacks/chip8/C8TECH10.HTM#2.1
- tombert 5y ago
  I forgot about CHIP-8. That might be a good starting point. Thanks for reminding me.
  - anthk 5y ago
    Try JimTCL, it uses SDL2 for "GUI"'s instead of TK, but it's as compatible (at code level, not TCL extensions, Jimsh uses its own ones) as TCL 8.5 so most stuff will work as is. If you look at the examples, you'll find that writing a Chip8 emulator with JimTCL it's a breeze. https://github.com/msteveb/jimtcl https://github.com/msteveb/jimtcl
deleted 5y ago
[deleted]
Gunax 5y ago
I wrote (or tried writing) a gameboy emulator once. My only qarning is that there are a lot of edge cases in the specification--and the proper specs are wrong. I ended up spending most of the time searching through undocumented/missing CPU specifications. It became rather tedious. For a learning project, this made it poorly suited. There are so many good emulators out there, the only reason to write one is for the learning experience. I just felt that I stopped oearning after a while and was just debugging obscure combinations of cpu states.
- tombert 5y ago
  That seems to be the consensus that I've read online. Still, the reason I want to do it online is specifically because I want an excuse to really understand low-level hardware. I (and probably a majority of people on HN who do software) really only have "real" experience with "Java or Higher" with maybe hitting C if I have the rare occasion of having to worry about saving a few milliseconds. An emulator would force me understand low level hardware, or at least I think it would.
  - coldpie 5y ago
    Another fun option for learning low-level stuff is analyzing existing games. I did this to create a level map dumper for one of my favorite NES games[1]. You can see other ideas on the excellent Displaced Gamers YouTube channel, for example[2]. Also, read the book Code by Charles Petzold. [1] https://tcrf.net/Proto:M.C._Kids#Level_Changes https://tcrf.net/Proto:M.C._Kids#Level_Changes [2] https://www.youtube.com/watch?v=zGdpst_6k9k https://www.youtube.com/watch?v=zGdpst_6k9k
  - yoyohello13 5y ago
    I think Nand 2 Tetris [1] is a really good way to get a good intro to this stuff at a basic level without too much friction with tools. You essentially start with a nand gate, and eventually build up a whole computer including a Java-like programming language. [1]: https://www.nand2tetris.org/ https://www.nand2tetris.org/
    - rjhallsted 5y ago
      I've been meaning to get to Nand2Tetris, it looks really interesting.
- aquova 5y ago
  That was more or less my experience. I got the original Game Boy working well, and quite a few Game Boy Color games, but it eventually devolved into debugging CPU timing issues and edge cases with sprite bugs. At some point I realized that I had gained all of the knowledge I had wished to learn and since my own emulator was never really going to do anything that hundreds of others weren't already doing better I moved on. I will say it was a good learning experience however. Chip-8 is a good start, but there are lots of concepts that emulating a Game Boy will require that Chip-8 does not.
eatonphil 5y ago
My unpopular opinion is to emulate an extremely reduced subset of x86. For example, jump to main and emulate the result of `int main() {return 2;}` compiled with gcc. You already have the compiler (no need to cross compile), you already have the decompiler and you can run the binary on the reference machine without an emulator. You save so much time having this entire toolchain already and you can start emulating simple C programs for x86 with <10 instructions and 1 or 2 addressing modes. I've written about this process before in Node and Go [0]. Yeah everyone will comment after me that x86 gets way more complex over time but if you just want to get a quick intro and you aren't a perfectionist x86 is kind of compelling. And recently I wanted to try emulating MSP341 at someone's recommendation because it has a very simple architecture. But just getting a C compiler for it isn't easy! When I've tried to cross-compile C to other archs like RISC-V it also wasn't straightforward and I just got stuck in this toolchain spot. If it were easier to cross-compile simple languages like C then writing emulators for other environments would be easier. If you're on a new Mac, my whole argument applies for aarch64 instead of x86. [0] https://notes.eatonphil.com/tags/emulators.html https://notes.eatonphil.com/tags/emulators.html
- gavinray 5y ago
  I thoroughly enjoyed what little I read of this, bookmarked it for later -- thanks! https://notes.eatonphil.com/emulating-amd64-starting-with-elf.html https://notes.eatonphil.com/emulating-amd64-starting-with-el...
- pizza234 5y ago
  > My unpopular opinion is to emulate an extremely reduced subset of x86 I don't think 808x is such an unpopular machine for approaching emulation. Some people use Space invaders (or contemporary titles), which is based on an 8080, as stepping stone between CHIP-8 and more modern (complex) platforms.
- ant6n 5y ago
  I wish there was an easy way to compile to a subset of x86 (e.g. mem access only with simple mov, only using one flag, no extensions, no floats, pure 32bit instructions).
agentultra 5y ago
Try your hand at a CHIP-8 emulator. The instruction set is really small, well documented, and easy to implement for your first project. https://multigesture.net/articles/how-to-write-an-emulator-chip-8-interpreter/ https://multigesture.net/articles/how-to-write-an-emulator-c...
djxfade 5y ago
My first "emulator" was a Brainfuck interpreter. Really simple to implement and understand
- tombert 5y ago
  That's a great idea! I think you win for my weekend project...if nothing else it will be fun to bring up that I made a Brainfuck compiler.
jjnoakes 5y ago
For a fun and fairly basic task, consider giving the 2019 advent of code a try. You will end up with a basic emulator for an imaginary machine, but you will get to solve interesting puzzles with it.
easterncalculus 5y ago
The UXN project might also be fun, the virtual machine is fairly simple to implement and there are a lot of interesting programs written for it. https://wiki.xxiivv.com/site/uxn.html There is also the LC3 virtual virtual machine, with a fairly great guide on creating it. https://justinmeiners.github.io/lc3-vm/
- entaloneralie 5y ago
  There's a Chip-8 emulator running on Uxn https://git.sr.ht/~rabbits/chip8uxn https://git.sr.ht/~rabbits/chip8uxn
mzs 5y ago
Emulating old terminals is fun.
toast0 5y ago
I've written somewhere around 1/3rd of a NES emulator. It does the CPU, and the backround half of the PPU, but not foreground sprites, sound, controllers, or running at decent speed ;) Anyhow, I found the CPU part a lot of fun, and there's public domain test roms with expected registers after each instruction that you can use to test and confirm. Interaction with other hardware and emulation of that hardware gets a lot more challenging. The gameboy is certainly different than the NES, but I suspect there's a lot of similarity at the high level. It's certainly reasonable to stop (or pause, perhaps), when it stops being so fun, too. I'm also not sure porting an emulator is going to give you the same understanding as writing one, but maybe.
- ltriant 5y ago
  I wrote a decently complete NES emulator[1], and the 6502 is definitely a fun CPU to emulate compared to other CPUs. The Z80-ish CPU in the Game Boy is not as fun, and as soon as you get into 68000 territory, it definitely stops being fun for a hobbyist. Getting the graphics and sound in sync with the CPU is a lot more challenging if you're looking to support many games, but if you just want to play some of the super simple early NES games, like Donkey Kong, then you can get away with a lot of inaccuracies. [1]: https://github.com/ltriant/nes https://github.com/ltriant/nes
CyberRabbi 5y ago
A nice perk of writing an emulator is the exposure you’ll get when it hits the front page of HN and other tech news sites.
hota_mazi 5y ago
Start with a CHIP-8 emulator, it's a great first emulator to write that will expose you to a lot of core concepts without all the complexity that comes with more advanced systems.
Cyph0n 5y ago
It is definitely a fun learning exercise, but also quite addictive and grueling (yes, a contradiction)! I wrote a Gameboy Color emulator[1] earlier this year, but stopped as soon as I realized that I wasn't learning anything new. As a result, my emulator has a few issues and does not support sound, but it is able to run quite a few games. I also got it running in a browser via WASM, which was fun. [1]: https://github.com/aksiksi/gbc https://github.com/aksiksi/gbc
AnIdiotOnTheNet 5y ago
If you think you can do it, you probably can. It's not really all that conceptually difficult until you want to do dynamic recompilation. I wrote my first emulator a while ago, for the Gigatron. People recommend CHIP-8 a lot but I just thought it looked too trivial and uninteresting. The Gigatron is still incredibly simple, but it's also a really elegant little beast worth studying for its own sake.

laputan_machine 5y ago

The first emulator I wrote was for a virtual machine called the CHIP-8. I used CowGod's reference, it was a fun experience! http://devernay.free.fr/hacks/chip8/C8TECH10.HTM#2.1 http://devernay.free.fr/hacks/chip8/C8TECH10.HTM#2.1

tombert 5y ago
I forgot about CHIP-8. That might be a good starting point. Thanks for reminding me.
- anthk 5y ago
  Try JimTCL, it uses SDL2 for "GUI"'s instead of TK, but it's as compatible (at code level, not TCL extensions, Jimsh uses its own ones) as TCL 8.5 so most stuff will work as is. If you look at the examples, you'll find that writing a Chip8 emulator with JimTCL it's a breeze. https://github.com/msteveb/jimtcl https://github.com/msteveb/jimtcl

deleted 5y ago

[deleted]

Gunax 5y ago

I wrote (or tried writing) a gameboy emulator once. My only qarning is that there are a lot of edge cases in the specification--and the proper specs are wrong. I ended up spending most of the time searching through undocumented/missing CPU specifications. It became rather tedious. For a learning project, this made it poorly suited. There are so many good emulators out there, the only reason to write one is for the learning experience. I just felt that I stopped oearning after a while and was just debugging obscure combinations of cpu states.

tombert 5y ago
That seems to be the consensus that I've read online. Still, the reason I want to do it online is specifically because I want an excuse to really understand low-level hardware. I (and probably a majority of people on HN who do software) really only have "real" experience with "Java or Higher" with maybe hitting C if I have the rare occasion of having to worry about saving a few milliseconds. An emulator would force me understand low level hardware, or at least I think it would.
- coldpie 5y ago
  Another fun option for learning low-level stuff is analyzing existing games. I did this to create a level map dumper for one of my favorite NES games[1]. You can see other ideas on the excellent Displaced Gamers YouTube channel, for example[2]. Also, read the book Code by Charles Petzold. [1] https://tcrf.net/Proto:M.C._Kids#Level_Changes https://tcrf.net/Proto:M.C._Kids#Level_Changes [2] https://www.youtube.com/watch?v=zGdpst_6k9k https://www.youtube.com/watch?v=zGdpst_6k9k
- yoyohello13 5y ago
  I think Nand 2 Tetris [1] is a really good way to get a good intro to this stuff at a basic level without too much friction with tools. You essentially start with a nand gate, and eventually build up a whole computer including a Java-like programming language. [1]: https://www.nand2tetris.org/ https://www.nand2tetris.org/
  - rjhallsted 5y ago
    I've been meaning to get to Nand2Tetris, it looks really interesting.
aquova 5y ago
That was more or less my experience. I got the original Game Boy working well, and quite a few Game Boy Color games, but it eventually devolved into debugging CPU timing issues and edge cases with sprite bugs. At some point I realized that I had gained all of the knowledge I had wished to learn and since my own emulator was never really going to do anything that hundreds of others weren't already doing better I moved on. I will say it was a good learning experience however. Chip-8 is a good start, but there are lots of concepts that emulating a Game Boy will require that Chip-8 does not.

eatonphil 5y ago

My unpopular opinion is to emulate an extremely reduced subset of x86. For example, jump to main and emulate the result of `int main() {return 2;}` compiled with gcc. You already have the compiler (no need to cross compile), you already have the decompiler and you can run the binary on the reference machine without an emulator. You save so much time having this entire toolchain already and you can start emulating simple C programs for x86 with <10 instructions and 1 or 2 addressing modes. I've written about this process before in Node and Go [0]. Yeah everyone will comment after me that x86 gets way more complex over time but if you just want to get a quick intro and you aren't a perfectionist x86 is kind of compelling. And recently I wanted to try emulating MSP341 at someone's recommendation because it has a very simple architecture. But just getting a C compiler for it isn't easy! When I've tried to cross-compile C to other archs like RISC-V it also wasn't straightforward and I just got stuck in this toolchain spot. If it were easier to cross-compile simple languages like C then writing emulators for other environments would be easier. If you're on a new Mac, my whole argument applies for aarch64 instead of x86. [0] https://notes.eatonphil.com/tags/emulators.html https://notes.eatonphil.com/tags/emulators.html

gavinray 5y ago
I thoroughly enjoyed what little I read of this, bookmarked it for later -- thanks! https://notes.eatonphil.com/emulating-amd64-starting-with-elf.html https://notes.eatonphil.com/emulating-amd64-starting-with-el...
pizza234 5y ago
> My unpopular opinion is to emulate an extremely reduced subset of x86 I don't think 808x is such an unpopular machine for approaching emulation. Some people use Space invaders (or contemporary titles), which is based on an 8080, as stepping stone between CHIP-8 and more modern (complex) platforms.
ant6n 5y ago
I wish there was an easy way to compile to a subset of x86 (e.g. mem access only with simple mov, only using one flag, no extensions, no floats, pure 32bit instructions).

agentultra 5y ago

Try your hand at a CHIP-8 emulator. The instruction set is really small, well documented, and easy to implement for your first project. https://multigesture.net/articles/how-to-write-an-emulator-chip-8-interpreter/ https://multigesture.net/articles/how-to-write-an-emulator-c...

djxfade 5y ago

My first "emulator" was a Brainfuck interpreter. Really simple to implement and understand

tombert 5y ago
That's a great idea! I think you win for my weekend project...if nothing else it will be fun to bring up that I made a Brainfuck compiler.

jjnoakes 5y ago

For a fun and fairly basic task, consider giving the 2019 advent of code a try. You will end up with a basic emulator for an imaginary machine, but you will get to solve interesting puzzles with it.

easterncalculus 5y ago

The UXN project might also be fun, the virtual machine is fairly simple to implement and there are a lot of interesting programs written for it. https://wiki.xxiivv.com/site/uxn.html There is also the LC3 virtual virtual machine, with a fairly great guide on creating it. https://justinmeiners.github.io/lc3-vm/

entaloneralie 5y ago
There's a Chip-8 emulator running on Uxn https://git.sr.ht/~rabbits/chip8uxn https://git.sr.ht/~rabbits/chip8uxn

mzs 5y ago

Emulating old terminals is fun.

toast0 5y ago

I've written somewhere around 1/3rd of a NES emulator. It does the CPU, and the backround half of the PPU, but not foreground sprites, sound, controllers, or running at decent speed ;) Anyhow, I found the CPU part a lot of fun, and there's public domain test roms with expected registers after each instruction that you can use to test and confirm. Interaction with other hardware and emulation of that hardware gets a lot more challenging. The gameboy is certainly different than the NES, but I suspect there's a lot of similarity at the high level. It's certainly reasonable to stop (or pause, perhaps), when it stops being so fun, too. I'm also not sure porting an emulator is going to give you the same understanding as writing one, but maybe.

ltriant 5y ago
I wrote a decently complete NES emulator[1], and the 6502 is definitely a fun CPU to emulate compared to other CPUs. The Z80-ish CPU in the Game Boy is not as fun, and as soon as you get into 68000 territory, it definitely stops being fun for a hobbyist. Getting the graphics and sound in sync with the CPU is a lot more challenging if you're looking to support many games, but if you just want to play some of the super simple early NES games, like Donkey Kong, then you can get away with a lot of inaccuracies. [1]: https://github.com/ltriant/nes https://github.com/ltriant/nes

CyberRabbi 5y ago

A nice perk of writing an emulator is the exposure you’ll get when it hits the front page of HN and other tech news sites.

hota_mazi 5y ago

Start with a CHIP-8 emulator, it's a great first emulator to write that will expose you to a lot of core concepts without all the complexity that comes with more advanced systems.

Cyph0n 5y ago

It is definitely a fun learning exercise, but also quite addictive and grueling (yes, a contradiction)! I wrote a Gameboy Color emulator[1] earlier this year, but stopped as soon as I realized that I wasn't learning anything new. As a result, my emulator has a few issues and does not support sound, but it is able to run quite a few games. I also got it running in a browser via WASM, which was fun. [1]: https://github.com/aksiksi/gbc https://github.com/aksiksi/gbc

AnIdiotOnTheNet 5y ago

If you think you can do it, you probably can. It's not really all that conceptually difficult until you want to do dynamic recompilation. I wrote my first emulator a while ago, for the Gigatron. People recommend CHIP-8 a lot but I just thought it looked too trivial and uninteresting. The Gigatron is still incredibly simple, but it's also a really elegant little beast worth studying for its own sake.