Table of content

What is this
57th Challenge
- Challenge
- Solution

What is this

The rules of the game are explained in my original.

57th Challenge

Challenge

Build on yesterday’s example and use the buzzer of the generic node to make a buzz! 📣 Here is a picture of the generic node again. Its a piece of hardware with an STM32WL5x and has a bunch of sensors and actuators as well as the possibility to use LoRaWAN.

Solution

Lets start from a template again, same folder as yesterday.

    cargo generate \
    --git https://github.com/stm32-rs/stm32wlxx-hal\
    --name stm32

The template, looks like this, when running tree -L 3

    .
    ├── CHANGELOG.md
    ├── Cargo.lock
    ├── Cargo.toml
    ├── LICENSE-APACHE
    ├── LICENSE-MIT
    ├── README.md
    ├── examples
    │   ├── Cargo.toml
    │   ├── examples
    │   └── src
    ├── hal
    │   ├── Cargo.toml
    │   └── src
    ├── lora-e5-bsp
    │   ├── Cargo.toml
    │   ├── README.md
    │   └── src
    ├── memory.x
    ├── nucleo-wl55jc-bsp
    │   ├── Cargo.toml
    │   ├── README.md
    │   └── src
    ├── rustfmt.toml
    └── testsuite
        ├── Cargo.toml
        ├── README.md
        ├── runall.py
        └── src

To run tests we run DEFMT_LOG=info cargo test -p testsuite --target thumbv7em-none-eabi --bin pka.

To keep things simple, we will add an additional example, instead of doing something complicated. The buzzer is a “Piezo speaker - provides audible feedback.” According to the documentation it is connected to PA15 - internally connected to the piezo speaker. The schematic can be found under following link. The relevant part looks as follows.

The datasheet of the buzzer MLT-7525 shows that the oscillation frequency is 2700Hz which you can listen to onyoutube - it sounds annoying. . So we must toggle the output at the resonant frequency of 2700 Hz, which means we need to toggle the GPIO every 185e-6 seconds. This means we toggle -> delay_us(185)permantently to activate the buzzer if we do it very simply and in a blocking manner.

    Michaels-MBP-10:stm32 michael$ DEFMT_LOG=trace cargo run-ex buzzer
        Blocking waiting for file lock on build directory
       Compiling defmt-macros v0.3.2
       Compiling defmt v0.3.2
       Compiling panic-probe v0.3.0
       Compiling defmt-rtt v0.3.2
       Compiling stm32wlxx-hal v0.6.1 (/Volumes/data/4_github/learn-rust/100-rust-snippets/stm32/hal)
       Compiling examples v0.1.0 (/Volumes/data/4_github/learn-rust/100-rust-snippets/stm32/examples)
        Finished dev [optimized + debuginfo] target(s) in 10.33s
         Running `probe-run --chip STM32WLE5JCIx --connect-under-reset target/thumbv7em-none-eabi/debug/examples/buzzer`
    (HOST) INFO  flashing program (11 pages / 11.00 KiB)
    (HOST) INFO  success!
    ────────────────────────────────────────────────────────────────────────────────
    INFO  Starting buzzer
    └─ buzzer::__cortex_m_rt_main @ examples/examples/buzzer.rs:27

And here we have it the result running on the target:

See the repo on as a fork of the original repos. For the lazy, here is the source embedded into this page:

    // Sounds a buzzer, will work only for TTN Generic node with STM32WL5x
    // see https://github.com/TheThingsIndustries/generic-node-se
    // The datasheet of the buzzer `MLT-7525` shows that the oscillation frequency is `2700Hz` so the period
    // is around 185us

    #![no_std]
    #![no_main]

    use defmt_rtt as _; // global logger
    use panic_probe as _; // panic handler

    use stm32wlxx_hal::{
        self as hal,
        cortex_m::{self, delay::Delay},
        gpio::{pins, Output, PinState, PortA},
        pac,
        util::new_delay,
    };

    #[hal::cortex_m_rt::entry]
    fn main() -> ! {
        let mut dp: pac::Peripherals = defmt::unwrap!(pac::Peripherals::take());
        let cp: pac::CorePeripherals = defmt::unwrap!(pac::CorePeripherals::take());

        let gpioa: PortA = PortA::split(dp.GPIOA, &mut dp.RCC);
        let mut buzzer: Output<pins::A15> =
            cortex_m::interrupt::free(|cs| Output::default(gpioa.a15, cs));

        let mut delay: Delay = new_delay(cp.SYST, &dp.RCC);

        defmt::info!("Starting buzzer");

        loop {
            for &level in &[PinState::High, PinState::Low] {
                buzzer.set_level(level);
                delay.delay_us(185);
            }
        }
    }