2. Explore build targets#

Throughout the Sense repository there are lots of BUILD.bazel files. Each BUILD.bazel file contains one or more targets. These targets are your entrypoints for doing lots of useful, common tasks, such as:

  • Building a binary

  • Running unit tests

  • Connecting to a device over a console

  • Flashing a binary to a device

When you’re starting a new Bazel-based project, you’ll need to create your own Bazel targets. When you’re ramping up on an existing Bazel codebase, these targets are a good way to get an overview of how the project works. Explore Sense’s Bazel targets now:

  1. Press Control+Shift+E (Command+Shift+E on macOS) to open the Explorer view.

  2. Within the Explorer list, expand the Bazel Build Targets section.

    Where is this?

    Look at the bottom left of your VS Code window. The source code is expanded by default so the Bazel Build Targets section gets pushed down to the far bottom. You can collapse the source code section (the one labeled Sense) to make the Bazel Build Targets section easier to find.

    https://storage.googleapis.com/pigweed-media/sense/20240802/build_targets.png

    This section provides an overview of all of the project’s build rules. Right-clicking a rule lets you build or run that rule. You’ll be using this UI a lot throughout the tutorial.

    Troubleshooting

    • The section is empty. Just wait a little bit. It should get populated after 30 seconds or so. It takes the Bazel extension some time to find all the Bazel targets.

    Note

    Although this UI is called Bazel Build Targets you may want to think of it instead as just Bazel Targets. This UI isn’t just used for building. You also use it to run tests, connect to a device over a console, and so on.

  3. Expand the //apps/blinky group.

    https://storage.googleapis.com/pigweed-media/sense/20240802/apps_blinky.png

    Note

    // means the root directory of your Sense repository. If you cloned Sense to ~/sense, then //apps/blinky would be located at ~/sense/apps/blinky.

  1. List all Bazel targets:

    $ bazelisk query //...

You should see output like this:

Starting local Bazel server and connecting to it...
//:copy_clangd
//:pw_console_config
//:refresh_compile_commands
//:refresh_compile_commands.check_python_version.py
//:refresh_compile_commands.py
//apps/blinky:blinky
//apps/blinky:flash
//apps/blinky:flash_rp2040
//apps/blinky:rp2040_blinky.elf
//apps/blinky:rp2040_console
//apps/blinky:rp2040_example_script
//apps/blinky:rp2040_toggle_blinky
//apps/blinky:rp2040_webconsole
//apps/blinky:simulator_blinky
//apps/blinky:simulator_console
//apps/blinky:simulator_webconsole
# ...

Here’s a quick summary of Sense’s targets:

  • //apps/<app>: Targets for building <app>, flashing <app> to a Pico, simulating <app> on your development host, and communicating with a device running <app> over a console. We’re using <app> as a placeholder here, the real app names are blinky, production, and so on. Note that there are different targets for building apps for different platforms, e.g. :rp2040_blinky.elf for building the binary that runs blinky on a Raspberry Pi RP2040 versus :simulator_blinky for the binary that runs on your development host.

  • //devices: Targets for building device drivers.

  • //modules/<module>: Targets for building platform-agnostic hardware abstraction layer modules.

  • //system: Targets for building the general middleware system that every application runs on top of.

  • //targets/<target>: Targets for compiling the applications for specific platforms such as the Raspberry Pi RP2040 MCU or your development host.

  • //tools: Targets for building and running tools that accompany the apps, such as the script for connecting to devices over pw_console.

Summary#

In a Bazel-based project, pretty much all common development tasks like building, flashing, connecting to devices, and so on are usually done through Bazel targets. Bazel makes it easy to see all targets at a glance. When onboarding onto a new project, browsing the list of targets can be a helpful way for building a top-down intuition about how the project works.

Next, head over to 3. Build the app to start building binaries the Bazel way.

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