01 - Blinky with logging

Blinky introduces the basics of building, flashing and checking log output. The instructions here will be the same for each exercise and binary to be flashed.

Rather than sitting in a blocking loop to blink an LED, this implementation uses timers to allow the device to do other work in between blinks.

Build and flash

  1. Build the firmware with pw build or pw watch.

  2. Flash blinky.elf.

    STM32F429I_DISC1 (Linux/MacOS)

    pw flash --device STM32-Discovery out/gn/stm32f429i_disc1_stm32cube.size_optimized/obj/examples/01_blinky/bin/blinky.elf

    Note

    We don’t yet have OpenOCD for Windows. See b/300986008 for updates.

    Raspberry Pi Pico (RP2404) (Windows/Linux/MacOS)

    1. Reboot the Pico into BOOTSEL mode by holding the bootsel button when plugging into USB.

    2. Copy ./out/gn/rp2040.size_optimized/obj/examples/01_blinky/blinky.uf2 to your Pi Pico.

    Note

    It is also possible to flash a Pico board with picotool. We will be adding support for that in this repo soon. See b/300321451 for updates.

View logs

Logs are tokenized and transmitted using pw_rpc. If you try to view the UART output using a serial terminal like minicom or screen, the device’s output will not be human-readable because the device is sending machine-readable binary data.

pw_console can take this binary data and turn it into human-readable logs and bidirectional RPC commands.

You can view the logs from your attached device with the following command:

Device

pw console -d /dev/ttyACM0 -b 115200 --token-databases out/gn/stm32f429i_disc1_stm32cube.size_optimized/obj/examples/01_blinky/bin/blinky.elf

Tip

On macOS, your device will look like /dev/cu.usbmodem2141403, but will most likely end with a different number.

Simulated device

The simulated device configures the porting layers (threading, communication, timers, etc.) used by this project to rely on native implementations. This allows you to run applications designed to run on embedded devices natively on your computer.

In this example, the LED porting layer is set up to just emit a log message rather than blink a physical LED.

When you launch a simulated device binary, it normally sits and waits for you to attach pw_console over a socket. From the console, you’ll then be able to see logs and issue commands. pw device-sim simplifies this by launching the simulated device as a background process and then immediately launching a console session that attaches to the simulated device.

  1. Build the firmware with pw build or pw watch.

  2. Launch blinky using the pw device-sim helper.

    pw device-sim ./out/gn/host_device_simulator.speed_optimized/obj/examples/01_blinky/bin/blinky

  3. When you’re finished, you can type quit in the Python Repl pane to exit.

Building with Bazel

In general, the sample project doesn’t support Bazel yet. But this example does!

To build and flash the firmware to the device run,

bazel run //examples/01_blinky:flash_stm32

Bazel knows that the flasher depends on the firmware, and will build the firmware image before flashing it. It will also track any changes to the firmware source and rebuild it before flashing if necessary.

If you do want to produce the .elf file but not flash it, run,

bazel build //examples/01_blinky:blinky.elf