Pigweed Developer Guide

Pigweed is an assortment of tooling and libraries for embedded projects. One of the key goals is that you may chose to use things from Pigweed in an à la carte fashion. Pigweed is a bundle of helper libraries, but it doesn't provide an application image that can be run on a device. Because of this, the binaries produced when building upstream Pigweed are unit tests (which can be directly flashed to a device and run) and host tools.

If you haven‘t already, you’ll need to go through the Pigweed setup process to ensure you have the necessary tools before running the commands throughout this guide.

Pigweed Environment

After going through the initial setup process, your current terminal will be in the Pigweed development environment that provides all the tools you should need to develop on Pigweed. If leave that session, you can activate the environment in a new session with the following command:


$ . activate.sh


> pw_env_setup\env_setup.bat

This will provide you with GN, Ninja, a host and Cortex-M compiler, clang-format, a recent version of Python, a kitted out Python virtual environment (venv), and more—all without messing with your current system configuration or requiring manual installation.

Building Pigweed With GN

Pigweed‘s primary build system is GN/Ninja based. There are CMake and Bazel builds in-development, but they are incomplete and don’t have feature parity with the GN build. We strongly recommend you stick to the GN build system.

GN (Generate Ninja) just does what it says on the tin; GN generates Ninja build files.

$ gn gen out/host

The default GN build configuration is set up to build with the host as the target (more on targets later). Note that out/host is the output directory that Ninja files are generated to, it doesn't imply any configuration. Now that the build files have been generated, you can begin the build using Ninja:

$ ninja -C out/host

Whenever you make changes to the source or build files, you only need to run ninja. Running GN again is only necessary if you delete your build directory and need to generate a new one.

No build system is perfect, so you might have the desire to clean your build directory if you're doubting the correctness of the build. Doing a clean build is relatively simple: delete the build directory out/[target], and re-generate it using gn gen.


Manually invoking the build can be tedious, though. You need to switch window focus and re-run Ninja. Fortunately, one of Pigweed's modules addresses this! pw_watch is a module that watches the Pigweed repository for changes to files with certain extensions.

To start pw_watch, simply run pw watch:

build example using pw watch

Whenever you modify files, pw watch will trigger a build for all the build subdirectories found in out/. Try it, you might be surprised how much time it can save you!

Running Unit Tests

Fun fact, you‘ve been running the unit tests already! Host builds automatically build and run the unit tests. Unit tests err on the side of being quiet in the success case, and only output test results when there’s a failure. If you want to try this out, modify one of the tests to fail:

example test failure using pw watch

Running tests as part of the build isn‘t particularly expensive because GN caches passing tests. Only affected tests are re-built/rerun on a code change (thanks to GN’s dependency resolution).

Selecting a Build Target

As mentioned previously, Pigweed builds for host by default. This builds unit tests and any host tools. In the context of Pigweed, a Pigweed “target” is a build configuration that sets a toolchain, default library configurations, and more to result in binaries that may be run natively on the target.

Here are some targets of interest:

  • Host (//targets/host/host.gni): Builds unit tests and host tools.

  • Docs (//targets/docs/target_config.gni): Builds these docs! This requires a build target because of the binary size reporting automatically generated with the documents.

  • STM32F429I-DISC1 (//targets/stm32f429i-disc1/target_config.gni): Builds unit tests for STMicroelectronics‘s Discovery development board (MPN: STM32F429I-DISC1). This is the device Pigweed uses for upstream development. It’s a relatively easy to acquire Cortex-M4 development board, and has an integrated STLink to simplify flashing and debugging of the device.

Rather than having tens or hundreds of exposed GN arguments that configure the build and are easy to accidentally modify, we use target configuration files that only expose arguments relevant to the target. This also makes it easier to check in changes to target configurations.

Setting the build target

To set the target configuration for a build, set the pw_target_config GN build arg to point to the target configuration .gni file you wish to use.

In this example, we generating Ninja build files for the stm32f429i-disc1.

$ gn gen --args='pw_target_config = "//targets/stm32f429i-disc1/target_config.gni"' out/disco

At this time, you may either run ninja -C out/disco or restart pw_watch to build for the STM32F429I-DISC1.

Running Tests on a Device

Even though we‘ve verified tests pass on the host, it’s critical to verify the same with the board. We've encountered some unexpected bugs that can only be found by running the unit tests directly on the device. This section will help you get set up to enable on-device testing integrated into the Ninja build (pw_watch comptible!) in three simple steps.

1. Connect Device(s)

Connect any number of STM32F429I-DISC1 boards to your computer using the mini USB port on the board (not the micro USB). Pigweed will automatically detect the boards and distribute the tests across the devices. More boards = faster tests!

2. Launch Test Server

To allow Ninja to run tests on an arbitrary number of devices, Ninja will send test requests to a server running in the background. Launch the server in another window using the command below (remember, you'll need to activate the Pigweed env first).

  $ stm32f429i_disc1_test_server

Note: If you attach or detach any more boards to your workstation you'll need to relaunch this server.

3. Configure GN

We can tell GN to use the testing server by enabling a build arg specific to the stm32f429i-disc1.

$ gn args out/disco
# Modify and save the args file to tell GN to run on-device unit tests.
pw_use_test_server = true


Whenever you make code changes and trigger a build, all the affected unit tests will be run across the attached boards!

Next steps

This concludes the introduction to developing with Pigweed. If you'd like to see more of what Pigweed has to offer, feel free to dive into the per-module documentation. If you run into snags along the way, please file bugs!