The alpaqa solvers can be used in embedded systems. This guide covers how to build the alpaqa examples for the Raspberry Pi Pico microcontroller, which is based on a dual-core ARM Cortex-M0+.

Dependencies

The only required dependency is the Eigen linear algebra library. It can be installed using the included install-eigen.sh script. Eigen is installed into the staging directory.

./scripts/install-eigen.sh "$PWD/staging" "RelWithDebInfo"

SDK and cross-compiler

You'll also need to install the Pico SDK and a suitable compiler:

mkdir -p ~/pico

git clone https://github.com/raspberrypi/pico-sdk ~/pico/pico-sdk --single-branch --branch 1.5.1

mkdir -p ~/opt

wget -O- https://github.com/tttapa/docker-arm-cross-toolchain/releases/latest/download/x-tools-arm-pico-eabi.tar.xz | tar xJ -C ~/opt

Configure and build the examples

A CMake toolchain file is included in cmake/toolchain/pico.cmake, it selects the correct options (disabling unsupported features such as loading of shared libraries), and loads the Pico SDK with the right compiler.

export PICO_SDK_PATH="$HOME/pico/pico-sdk"
export PICO_GCC_TRIPLE="arm-pico-eabi"
export PICO_TOOLCHAIN_PATH="$HOME/opt/x-tools/arm-pico-eabi/bin"
cmake -S . -B build -G Ninja \
    --toolchain cmake/toolchain/pico.cmake \
    -D Eigen3_DIR="$PWD/staging/share/eigen3/cmake" \
    -D CMAKE_BUILD_TYPE=Release
cmake --build build -j

Copy the example to the Pico

Connect the Pico over USB while pressing the BOOTSEL button to enter programming mode. Then copy the UF2 file to the storage device that appears.

cp build/examples/C++/CustomCppProblem/custom-cpp-problem-example.uf2 /media/$USER/RPI-RP2

Open the serial port output

screen /dev/ttyACM0 115200

You should see the solver progress and the solution printed.

VSCode support

When using the CMake Tools extension in VSCode, you can select the RPi Pico ─ tttapa/arm-pico-eabi kit to compile for the Pico. You can edit the .vscode/cmake-kits.json file to set the paths to the compiler and the Pico SDK.