Saturnus

An open-source reimplementation of the modern RTOS microkernel "HorizonKernel" that is used in the Nintendo Switch.

About

The original Horizon kernel is written in modern C++ using a design heavily based on reference-counted C++ objects. As a microkernel, it has a custom IPC system and being a custom design, it has zero POSIX compatibility elements.

A combination of these factors makes up for a very interesting research project to see how well the Rust language can handle the design of this kernel in its essence, while also providing semantic equivalence to the original kernel.

That being said, the goal is not to generate matching binaries to the original but to have an idiomatic open source reference of this masterpiece while pushing Rust's boundaries and exploring the capabilities of this language in the process. Maybe we will also extinguish Linux from the world of embedded software for good as a side effect.

Code Organisation

TODO: Write me.

Building and Testing

Dependencies and cargo-xtask

Saturnus uses cargo-xtask as it's build system which can be invoked by running cargo xtask in the project directory. Execute cargo xtask help to see all possible commands xtask can execute.

This has the advantage that the only dependency required to build Saturnus is Rust itself and all the components of the Rust toolchain specified in the rust-toolchain.toml file. These will automatically be installed by rustup if you enter the project directory.

Building and Running

To build and run the Saturnus Kernel in QEMU execute the following command

cargo kernel run --release

cargo kernel is an alias for cargo xtask -p kernel (see .cargo/config.toml for all aliases) and thus can be used to execute each action provided by xtask:

# Only build the kernel in debug mode
cargo kernel build

# Run one of the LLVM bintools on the produced kernel binary
cargo kernel llvm size

Since Saturnus is composed of multiple packages, all these commands also work for other packages (e.g. the loader: cargo loader build / cargo xtask -p loader build).

For a complete and up-to-date overview run cargo xtask help.

Testing

TODO: Write once we have proper tests

Contributing

Because of the official status as a research project and the required familiarity with the original system, this project is unlikely to accept significant code contributions from people that are not project developers without prior bikeshedding discussion.

Code quality improvements, additional documentation and bugfixes to the existing codebase are encouraged and heavily appreciated anytime!

License

Saturnus notably consists of the Kernel itself and its corresponding bootstrap loader, which can be found under kernel/, and its library ecosystem under crates/.

The kernel and its loader are licensed under the terms of the GNU General Public License v2. See LICENSE-GPL for more details.

The library ecosystem, on the other hand, is designed to be re-usable in the world of embedded Cortex-A, and is therefore dual-licensed under the terms of either the Apache License (Version 2.0) or the MIT license, at the user's choice. See LICENSE-APACHE and LICENSE-MIT for details.

Contributions to a specific component of the Saturnus project must be made under the terms of all licenses it is governed by.