Bazel build

Using the Pico SDK in a Bazel project.

Add pico-sdk as a dependency

First, in your MODULE.bazel file, add a dependency on the Pico SDK:

bazel_dep(
  name = "pico-sdk",
  version = "2.0.0",
)

Second, in the same file you‘ll need to add an explicit dependency on rules_cc, as it’s a special-cased Bazel module:

# Note: rules_cc is special-cased repository; a dependency on rules_cc in a
# module will not ensure that the root Bazel module has that same version of
# rules_cc. For that reason, this primarily acts as a FYI. You'll still need
# to explicitly list this dependency in your own project's MODULE.bazel file.
bazel_dep(name = "rules_cc", version = "0.0.9")

# rules_cc v0.0.10 is not yet cut, so manually pull in the desired version.
# This does not apply to dependent projects, so it needs to be copied to your
# project's MODULE.bazel too.
archive_override(
    module_name = "rules_cc",
    urls = "https://github.com/bazelbuild/rules_cc/archive/1acf5213b6170f1f0133e273cb85ede0e732048f.zip",
    strip_prefix = "rules_cc-1acf5213b6170f1f0133e273cb85ede0e732048f",
    integrity = "sha256-NddP6xi6LzsIHT8bMSVJ2NtoURbN+l3xpjvmIgB6aSg=",
)

Register toolchains

These toolchains tell Bazel how to compile for ARM cores. Add the following to the MODULE.bazel for your project:

register_toolchains(
    "@pico-sdk//bazel/toolchain:linux-x86_64-rp2040",
    "@pico-sdk//bazel/toolchain:linux-x86_64-rp2350",
    "@pico-sdk//bazel/toolchain:win-x86_64-rp2040",
    "@pico-sdk//bazel/toolchain:win-x86_64-rp2350",
    "@pico-sdk//bazel/toolchain:mac-x86_64-rp2040",
    "@pico-sdk//bazel/toolchain:mac-x86_64-rp2350",
    "@pico-sdk//bazel/toolchain:mac-aarch64-rp2040",
    "@pico-sdk//bazel/toolchain:mac-aarch64-rp2350",
)

Enable required .bazelrc flags

To use the toolchains provided by the Pico SDK, you‘ll need to enable a few new features. In your project’s .bazelrc, add the following

# Required for new toolchain resolution API.
build --incompatible_enable_cc_toolchain_resolution
build --@rules_cc//cc/toolchains:experimental_enable_rule_based_toolchains

Ready to build!

You‘re now ready to start building Pico Projects in Bazel! When building, don’t forget to specify --platforms so Bazel knows you're targeting the Raspberry Pi Pico:

$ bazelisk build --platforms=@pico-sdk//bazel/platform:rp2040 //...

SDK configuration

An exhaustive list of build system configuration options is available in //bazel/config:BUILD.bazel.

Selecting a different board

A different board can be selected specifying --@pico-sdk//bazel/config:PICO_BOARD:

$ bazelisk build --platforms=//bazel/platform:rp2040 --@pico-sdk//bazel/config:PICO_BOARD=pico_w //...

If you have a bespoke board definition, you can configure the Pico SDK to use it by pointing --@pico-sdk//bazel/config:PICO_CONFIG_HEADER to a cc_library that defines PICO_BOARD and either a PICO_CONFIG_HEADER define or a pico/config_autogen.h header. Make sure any required includes, hdrs, and deps are also provided.

Generating UF2 firmware images

Creation of UF2 images can be done as explicit build steps on a per-binary rule basis, or through an aspect. Running a wildcard build with the pico_uf2_aspect enabled is the easiest way to create a UF2 for every ELF firmware image.

$ bazelisk build --platforms=@pico-sdk//bazel/platform:rp2040 \
    --aspects @pico-sdk//tools:uf2_aspect.bzl%pico_uf2_aspect \
    --output_groups=+pico_uf2_files \
    //...

Building the Pico SDK itself

First time setup

You'll need Bazel (v7.0.0 or higher) or Bazelisk (a self-updating Bazel launcher) to build the Pico SDK.

We strongly recommend you set up Bazelisk.

You will also need a working compiler configured if you wish to build Picotool or pioasm.

  • Linux: sudo apt-get install build-essential or similar.
  • macOS: xcode-select --install
  • Windows: Install MSVC

Building

To build all of the Pico SDK, run the following command:

$ bazelisk build --platforms=//bazel/platform:rp2040 //...

Known issues and limitations

The Bazel build for the Pico SDK is relatively new, but most features and configuration options available in the CMake build are also available in Bazel. You are welcome and encouraged to file issues for any problems and limitations you encounter along the way.

Currently, the following features are not supported:

  • The pioasm parser cannot be built from source via Bazel.
  • Windows MSVC wildcard build (bazel build //...) does not work when targeting host.
  • Bazel does not yet provide RISC-V support for Pico 2/RP2350.
  • Pico W wireless libraries have link issues.

Contributing

When making changes to the Bazel build, please run the Bazel validation script to ensure all supported configurations build properly:

$ ./tools/run_all_bazel_checks.py

If you need to check against a local version of Picotool, you can run the script with --picotool-dir:

$ ./tools/run_all_bazel_checks.py --picotool-dir=/path/to/picotool