TinyGo - Go compiler for microcontrollers

We never expected Go to be an embedded language and so it's got serious problems [...].

-- Rob Pike, GopherCon 2014 Opening Keynote

TinyGo is a project to bring Go to microcontrollers and small systems with a single processor core. It is similar to emgo but a major difference is that I want to keep the Go memory model (which implies garbage collection of some sort). Another difference is that TinyGo uses LLVM internally instead of emitting C, which hopefully leads to smaller and more efficient code and certainly leads to more flexibility.

My original reasoning was: if Python can run on microcontrollers, then certainly Go should be able to and run on even lower level micros.

Example program (blinky):

import (
    "machine"
    "time"
)

func main() {
    led := machine.GPIO{machine.LED}
    led.Configure(machine.GPIOConfig{Mode: machine.GPIO_OUTPUT})
    for {
        led.Low()
        time.Sleep(time.Millisecond * 1000)

        led.High()
        time.Sleep(time.Millisecond * 1000)
    }
}

Currently supported features:

control flow
many (but not all) basic types: most ints, floats, strings, structs
function calling
interfaces for basic types (with type switches and asserts)
goroutines (very initial support)
function pointers (non-blocking)
interface methods
standard library (but most packages won't work due to missing language features)
slices (partially)
maps (very rough, unfinished)
defer
closures
bound methods
complex numbers (except for arithmetic)
channels (with some limitations)

Not yet supported:

select
complex arithmetic
garbage collection
recover
introspection (if it ever gets implemented)
...

Installation

See the getting started instructions.

Running with Docker

A docker container exists for easy access to the tinygo CLI:

$ docker run --rm -v $(pwd):/src tinygo/tinygo tinygo build -o /src/wasm.wasm -target wasm examples/wasm

Note that you cannot run tinygo flash from inside the docker container, so it is less useful for microcontroller development.

Supported targets

The following architectures/systems are currently supported:

ARM (Cortex-M)
AVR (Arduino Uno)
Linux
WebAssembly

For more information, see this list of targets and boards. Pull requests for broader support are welcome!

Analysis and optimizations

The goal is to reduce code size (and increase performance) by performing all kinds of whole-program analysis passes. The official Go compiler doesn't do a whole lot of analysis (except for escape analysis) because it needs to be fast, but embedded programs are necessarily smaller so it becomes practical. And I think especially program size can be reduced by a large margin when actually trying to optimize for it.

Implemented compiler passes:

Analyse which functions are blocking. Blocking functions are functions that call sleep, chan send, etc. Its parents are also blocking.
Analyse whether the scheduler is needed. It is only needed when there are go statements for blocking functions.
Analyse whether a given type switch or type assert is possible with type-based alias analysis. I would like to use flow-based alias analysis in the future, if feasible.
Do basic dead code elimination of functions. This pass makes later passes better and probably improves compile time as well.

Scope

Goals:

Have very small binary sizes. Don't pay for what you don't use.
Support for most common microcontroller boards.
Be usable on the web using WebAssembly.
Good CGo support, with no more overhead than a regular function call.
Support most standard library packages and compile most Go code without modification.

Non-goals:

Using more than one core.
Be efficient while using zillions of goroutines. However, good goroutine support is certainly a goal.
Be as fast as gc. However, LLVM will probably be better at optimizing certain things so TinyGo might actually turn out to be faster for number crunching.
Be able to compile every Go program out there.

A long tail of small (and large) language features haven't been implemented yet. In almost all cases, the compiler will show a todo: error from compiler/compiler.go when you try to use it. You can try implementing it, or open a bug report with a small code sample that fails to compile.
Lots of targets/boards are still unsupported. Adding an architecture often requires a few compiler changes, but if the architecture is supported you can try implementing support for a new chip or board in src/runtime. For details, see this wiki entry on adding archs/chips/boards.
Microcontrollers have lots of peripherals and many don't have an implementation yet in the machine package. Adding support for new peripherals is very useful.
Just raising bugs for things you'd like to see implemented is also a form of contributing! It helps prioritization.

License

This project is licensed under the BSD 3-clause license, just like the Go project itself.