Embedded Swift on the Raspberry Pi Pico

A proof of concept for executing Embedded Swift code on the Raspberry Pi Pico. The main program is written in C (built with the official Pico C SDK) and calls into a statically linked Swift library.

Prerequisites and Installation

Hardware

• A Raspberry Pi Pico
• Optional but recommended: a Raspberry Pi Debug Probe for more convenient flashing

Software

• Host OS: macOS 13.x or 14.x

  Tested on macOS 13.6.2. It’ll probably work on Linux with minimal modifications to tell CMake how to find the Swift toolchain, but I haven’t tested this.

• A recent nightly Swift toolchain from swift.org. Tested with the Xcode toolchain from December 7, 2023.

• A clone of the Raspberry Pi Pico C/C++ SDK:

  cd ..
  git clone https://github.com/raspberrypi/pico-sdk.git
  cd pico-sdk/
  git submodule update --init
  cd ..

  This project expects to find the SDK in a sibling directory named pico-sdk. You can change this below if your SDK is in a different place.

• The GCC compiler for ARM embedded platforms

• CMake and Ninja:

  brew install cmake ninja

  The Pico SDK uses CMake as its build system and we’re piggybacking on that. The Swift library is also built with CMake. The unfortunate consequence is that we can’t easily use a SwiftPM package for the Swift library as we’d have to tell CMake how to build the package.

Configuration

Open the file CMakeLists.txt in the root folder. Edit these two lines to match your setup:

…
set(PICO_SDK_PATH "${CMAKE_CURRENT_LIST_DIR}/../pico-sdk")
…
set(Swift_Toolchain "org.swift.59202312071a")
…

Building

cd pico-embedded-swift
mkdir build
cd build
cmake -G Ninja ..
ninja

This produces the executable SwiftPico.elf in the build directory.

Running on the Pico

You have two options to copy the executable to the Pico:

1. Via the USB Mass Storage interface: use the provided build/elf2uf2/elf2uf2 tool to convert the .elf file to .uf2.

2. Via the debug probe. I use probe.rs for this, which is a tool from the Rust community, but it works in this context too:

   probe-rs run --chip RP2040 SwiftPico.elf