Rust snippet using avr-hal: Manual PWM to pull a digital output pin on an arduino to specified Hertz frequency. Useful to operate buzzers.

frequency.rs

use arduino_hal::{clock::Clock,port::{mode::Output, Pin, PinOps}};

/// Pull an arduino's output pin to specified Hertz for microseconds duration.
/// This is essentially manual PWM, without avr-hal's clock prescaling. 
/// Useful to make buzzers oscillate at 440 hertz.
/// This is not measured to be precise but works well enough.
///
/// example:
/// let dp = arduino_hal::Peripherals::take().unwrap();
/// let pins = arduino_hal::pins!(dp);
/// let mut buzzer_pin = pins.d2.into_output()
/// pin_to_hz_for_duration_us(&mut buzzer_pin, 440, 2 * 10_u32.pow(6)) // pin d2 buzzes at 440hz for 2 seconds.
fn pin_to_hz_for_duration_us<P: PinOps> (pin: &mut Pin<Output, P>, frequency_hz: u32, duration_us: u32) {
    if frequency_hz == 0 {
        // can't meaningfully wait 
        arduino_hal::delay_us(duration_us);
        return;
    }

    const CLOCK_SPEED_HZ: u32 = arduino_hal::DefaultClock::FREQ;
    let wait_time = (CLOCK_SPEED_HZ / frequency_hz) / 100;

    let mut acc = 0;
    while acc < duration_us {
        pin.set_high();
        arduino_hal::delay_us(wait_time / 2);
        pin.set_low();
        arduino_hal::delay_us(wait_time / 2);
        acc += wait_time;
    }
}