What if Rust, on GameTank?
The GameTank is a retro-inspired game console running dual 6502 processors. It has 128x128 composite out, with up to 200 colors. It's kind of like if Pico8 were real hardware -- with real hardware limitations, and neat tricks!
I like Rust, I like GameTank. What if, both?
Rust compiles via LLVM. There is LLVM-MOS, which can target the 6502. Throw all that together and create some linker scripts, we should have a stew.
This repository is basically the rust SDK for the gametank. As such, I've included a few utilities to make life easier.
First thing is a docker container where I've built llvm-mos + rust-mos, and a few utilities to make life easier.
Just run the container with the project directory mounted as a volume. You'll get access to a fully configured llvm/rust-mos toolchain within the container, while also being able to edit code in your local editor. I use IntelliJ as my IDE of choice, with an interactive terminal into the container at the bottom.
docker pull dwbrite/rust-mos:gametank-edition
docker run -it --rm -v ./:/workspace:z dwbrite/rust-mos:gametank-edition
On Windows/WSL, you may need to modify the workspace volume URL.
I would recommend creating your project as a new example, since it's slightly easier than creating a whole template from this repository.
The justfile is a sort of living document and handy tool for your workflow. The docker container even includes autocomplete for just.
Most of the time you only need just build-example <example-name>, which produces an output.bin file you can load into the emulator.
Unfortunately, the current version of rust-mos doesn't support inline assembly. We work around this by including assembly as a single static library, compiled from every .asm file found (recursively) in this directory. This solution is okay, only because dead code is shaken out by the linker.
This also means that functions aren't often (ever?) inlined in the final binary, and there may be some weird issues with function calls to assembly being jmp rather than jsr. Not sure what that's about.
You can find programming information about the gametank at the gametank wiki, the programming manual, as well as some examples/games in C and assembly on Clyde's github. For example: Accursed Fiend
The best example right now is examples/microvoid, programmed in two weeks for the first ever GameTank Game Jam. It implements much of what should be refactored into the SDK.
signal-2023-12-28-07-56-39-179.mp4
It's got some issues that have yet to be debugged, and in its current state only works on the desktop emulator or in the emulator on clyde's website, after a hard reset. I think the issue has something to do with llvm thinking the stack is initialized when it's not. I may have to clear the reserved registers in asm before __boot() 🤔
It's also programmed against a theoretical 32K cartridge, whereas most physical cartridges use 2MB flash, which needs to be banked on first use.