Lately, I’ve been more interested in learning about emulators and interpreters, down to the way that CPUs work at a low level. In university, the furthest down we got was C++ and we didn’t spend that much time there, so everything under that has always felt a little like black magic to me. To overcome that, I took a look into what it would take to write a toy emulator.
After briefly considering an NES emulator as my first project, I discovered the CHIP-8 VM and decided that would make a really neat first project. There are lots of resources for the CHIP-8 and it’s also a simple implementation, which means it can be done over a weekend or even faster.
I decided to write the emulator using Rust, a systems programming language that I’ve been dabbling in on and off whenever I feel like taking a break from Java. In the past, I would have dabbled in C or C++ but as time goes by, I feel that it makes more sense to focus on Rust.
Why?
Like C and C++, Rust compiles down to native code and runs without the overhead of a VM while also giving you full access to the platform underneath. Unlike C and C++, it also has some nice features that make it feel modern and fresh, like memory safety without garbage collection, super-charged enums, and a great build system that has built-in support for dependencies, unit testing, and more.
In fact, the only real beef I have with Rust is that it’s still young, so its support for mobile development is not quite up to par with the C and C++ support provided by Apple and Google. I’m sure this will improve with time. (After spending some time with Swift, I would also wish for no semicolons and maybe nicer optional unwrapping, but, at least with the semicolons, that ship has probably already sailed. :))
By writing the interpreter in Rust and taking advantage of the unit test features, it was very easy to build up the CHIP-8 VM, and I only ended up with a couple of pesky logic bugs due to being unsure about the implementation in a couple of places and due to a misuse of the slicing syntax.
Once I was done with the Rust implementation, I just copy-pasted the whole thing into Javascript, which you can check out at the end of this post. The code is available on GitHub, and here are a couple of other implementations you can also check out:
Kotlin CHIP-8 (badlogic) (Let’s write a Chip8 emulator in Kotlin)
Rust CHIP-8 (Notch)
I would also recommend checking out nand2tetris, a really interesting course which teaches you how to build your own toy CPU from NAND gates. The course can be audited for free on Coursera.
In the future, instead of copy/pasting to JS, I might be able to just compile straight to WebAssembly:
Compiling Rust to your Browser
Compiling Rust to WebAssembly Guide
I really like where Rust is going and hope to see a lot more progress in 2017. Happy New Year, and here’s to a great 2017 for all. 🙂