OC-Wasm is a CPU architecture for OpenComputers which executes WebAssembly binaries.

To get a basic “hello world”-type application running with OC-Wasm, you’ll need to follow a few steps:

• Build a computer. OC-Wasm doesn’t add any new items; instead, you use the standard OpenComputers items, just as if you were building a Lua computer. After crafting the CPU or APU, hold it in your hand and Shift-Right-Click to switch architectures—just like you would to switch between Lua 5.2 and 5.3—and you should see WebAssembly in the list.
• All computers need a BIOS, and WebAssembly computers are no different. If your program is very small (≤4 kiB), you can put it directly on an EEPROM and use it as a BIOS directly. Usually, though, your program will be too big to fit on an EEPROM, so you’ll want a BIOS which can load your program from disk. OC-Wasm-BIOS does just that: it loads a program from /init.wasm on a disk (just like the Lua BIOS loads a program from /init.lua). Since there’s no craftable item that comes with a BIOS, you’ll need to download the BIOS onto an existing computer (presumably running Lua, e.g. via wget) and flash it onto an EEPROM (e.g. via flash).
• Create your application. You’ll probably do this outside Minecraft, using regular software development tools. Once you’ve compiled a .wasm file, name it init.wasm and place it in the root directory of a hard drive or floppy disk. This can be done a few different ways:
  • Upload your program to the Internet, put the disk in a working computer, download the file to it with wget, and move the disk to the new computer.
  • Place the file directly in the proper place in your Minecraft save game directory, if you have access to it. You probably want to set bufferChanges to false in the filesystem section of your OpenComputers config file if you’re regularly using this method.
• Boot your computer!

A number of crates are available to make writing OC-Wasm programs in Rust ergonomic:

• OC-Wasm-Cassette provides an easy way to use the Cassette async executor to run an async fn as your main function.
• OC-Wasm-Sys is a set of raw FFI bindings. You probably don’t want to use this crate directly, but it underpins all the other ones.
• OC-Wasm-Safe is a set of wrappers around OC-Wasm-Sys that provide memory safety, safe handling of opaque value descriptors, and mutual exclusion over system calls that cannot be invoked multiple times simultaneously.
• OC-Wasm-Futures is a set of async futures that make it easier to write an OC-Wasm program using async and await.
• OC-Wasm-OpenComputers is a set of high-level wrappers around the component APIs supported by ordinary OpenComputers (such as the redstone API, the filesystem API, the GPU API, etc.).

As of this writing, OC-Wasm-OpenComputers is incomplete, and there are no crates for high-level wrappers around other mods that can interact with OpenComputers (e.g. via the adapter block); however, community contributions (in the form of merge requests to OC-Wasm-OpenComputers or new crates for content from mods) are very welcome!

AmandaC from the OpenComputers community has started early work on a repository with a Zig library and a few small examples for OC-Wasm.

If you want to work in a language which doesn’t already have support libraries, or you’re just curious how things work under the hood, please have a look at the OC-Wasm Javadoc.