picofuse

Motivation

Picofuse is a software system for hardware-independent development of small event-driven applications. It provides a common interface for hardware peripherals and a build system that abstracts away the details of the underlying hardware. There are a variety of modules which define the abstraction.

Module hierarchy

• sys: System-level functions.
• hw : Hardware for peripherals such as GPIO, I2C, SPI, etc.
• dev : Device implementation for specific components.
• net: Network stack for TCP/IP communication.
• fs : Filesystem abstraction for persistent storage.
• pix: Graphics library for drawing on displays.
• wav: Audio library for playing and recording sound.
• hid: Human Interface Device library for handling input devices, such as keyboards, button and mice, plus sensor readings.
• app: Application framework for event-driven programming.

A standalone, per-board "picofuse" installation is built, together with its headers and pkg-config metadata, installed under a plain directory prefix (e.g. /opt/picofuse/<board>).

Use

(under development)

• Download the picofuse library, which contains some supported boards, platforms and architectures.
• Use the API documentation for reference, and examine the samples.

You can then build a real .elf for that board using nothing but CMake, pkg-config and the compiler toolchain, via the picofuse_executable() helper installed alongside the prefix (see examples/helloworld):

cmake_minimum_required(VERSION 3.20)
project(helloworld C)

include(/opt/picofuse/<board>/cmake/picofuse_executable.cmake)

picofuse_executable(
    NAME helloworld
    LIBRARIES picofuse-sys
    SOURCES helloworld.c
)

The following shell commands set up the environment for building the example:

export PKG_CONFIG_PATH=/opt/picofuse/<board>/lib/pkgconfig
# Use -DPICO_BOARD=<board> to specify the target board
cmake -S . -B build

# Build
cmake --build build

The aim is that prototyping can be performed on a host computer, while deployment to the target hardware (such as Raspberry Pi or Pico) is seamless and requires minimal changes to the code. The executable (or .elf file) will be located in the corresponding build directory, for flashing to the embedded device or executable on the host system.

Development

The following sections assume you are wishing to adapt or otherwise develop the picofuse library.

Requirements

• The third_party/pico-sdk submodule (pinned to pico-sdk 2.3.0), which itself pulls in further submodules - tinyusb, btstack, cyw43-driver, lwip, mbedtls. make initializes it recursively as part of configure, so there's no need to run git submodule update manually.
• An ARM GNU Toolchain (arm-none-eabi-gcc and friends) on PATH.
• CMake 3.20+.
• Python 3 (used by pico-sdk's own build for code generation and picotool).

Pico targets are self-contained, thanks to the Pico SDK. For host builds (Linux, Darwin), the following dependencies enable optional features - required ones are needed for the build to succeed at all, optional ones are only needed to enable the corresponding feature:

Dependency	macOS (Homebrew)	Debian/Raspberry Pi OS
OpenSSL (required)	brew install openssl@3	sudo apt install libssl-dev
WPA Supplicant (optional, for WiFi support)	N/A	sudo apt install libwpa-client-dev
Mosquitto (optional, for MQTT support)	brew install mosquitto	sudo apt install libmosquitto-dev
USB (optional, for USB support)	brew install libusb pkgconf	sudo apt install libusb-1.0-0-dev

Build & Install

Use make to configure and build:

make

By default this builds for the host (CMAKE_BUILD_TYPE=Release) into build/. Set PICO_BOARD to cross-compile for a specific board/chip combination, and CMAKE_BUILD_TYPE to change the build type (e.g. Debug):

# Pico (RP2040)
make PICO_BOARD=pico BUILD_DIR=build-pico

# Pico W (RP2040 + CYW43 Wi-Fi/Bluetooth)
make PICO_BOARD=pico_w BUILD_DIR=build-pico_w

# Pico 2 (RP2350)
make PICO_BOARD=pico2 BUILD_DIR=build-pico2

# Pico 2 W (RP2350 + CYW43)
make PICO_BOARD=pico2_w BUILD_DIR=build-pico2_w

# Debug build
make CMAKE_BUILD_TYPE=Debug

BUILD_DIR defaults to build - set it to keep per-board build trees separate, as above.

Install with:

make install

This builds and installs into PREFIX (defaults to BUILD_DIR, i.e. build/). Combine with PICO_BOARD and BUILD_DIR/PREFIX to install a per-board prefix, e.g.:

make PICO_BOARD=pico BUILD_DIR=build-pico PREFIX=/opt/picofuse/pico install

Installing produces, under the chosen prefix:

• lib/libpicosdk.a, lib/libpicofuse_sys_pico.a
• include/ - every SDK module's headers merged into one consolidated tree, plus picofuse/ and runtime/
• lib/pkgconfig/picosdk.pc, lib/pkgconfig/picofuse_sys_pico.pc (the latter Requires: picosdk, so pulling it in via pkg-config also pulls in picosdk's own flags)
• lib/picosdk/src/ - the linker script fragments the .pc file's Libs point at

We'd like to provide pre-compiled per-board libraries (so consumers don't need to build pico-sdk themselves) soon.

Testing

Run the test suite on the host with:

cd picofuse
make test

If you are on a Mac and want to run the tests for different operating systems and architectures, you can use the following commands to test on both gcc and clang compilers:

cd picofuse

# build
ARCH=$(uname -m) # Use arm64 or x86_64 to build for different architectures
docker buildx build -f docker/Dockerfile.trixie --build-arg PLATFORM=${ARCH} --tag trixie-builder .

# test with different compilers
docker run --rm -i -v $(pwd):/root trixie-builder bash -c "make clean && CC=gcc make test"
docker run --rm -i -v $(pwd):/root trixie-builder bash -c "make clean && CC=clang make test"

Note: tests do not yet run when cross-compiling for a Pico board (i.e. with PICO_BOARD set) - they currently only work for host builds. It's envisaged that testing on Pico boards will require a Pico probe to work.

Examples

Example applications are available in the [examples](examples) folder (currently blink and helloworld), showing how to build a real application against an installed prefix.

Documentation

API documentation is generated in Doxygen format:

make doc

This requires Docker, and writes the generated documentation into the doc folder.

Licensing

This project is licensed under the [Apache License 2.0](LICENSE). It builds against third-party components with their own licenses (BSD, MIT, Apache-2.0/GPL) - see NOTICE.md for details. Issues and pull requests are welcome.