Limitation in From<MicroSecond> for Hertz: Cannot configure timers for periods > 1s

[Patricio-Andre]

I've encountered a runtime panic when trying to initialize a countdown timer with a duration longer than 1 second. The issue stems from the integer arithmetic used when converting MicroSecond durations into Hertz.

Because the HAL attempts to convert the duration into a frequency, any duration longer than 1 second results in a frequency lower than 1 Hz. Since Hertz wraps an integer, this truncates to 0, triggering the assertion.

// This is the absolute maximum allowed
let mut count_down_timer = timer.start_count_down(1000.ms());

However, increasing the duration by just 1ms causes a panic.
Root Cause In the implementation of From for Hertz:

impl From<MicroSecond> for Hertz {
    fn from(period: MicroSecond) -> Hertz {
        assert!(period.0 > 0 && period.0 <= 1_000_000);
        Hertz(1_000_000 / period.0)
    }
}

The STM32 hardware timers are capable of counting periods much longer than 1 second (using appropriate prescalers and ARR values). The HAL API should support passing Duration directly to start_count_down without forcing a lossy conversion to Hertz, or at least support a milliHertz type to allow lower frequencies.

Alternatively, if Hertz is strictly required, we might need a workaround for frequencies <1 Hz.