drogue-embedded-timer

When writing device drivers against embedded-hal, a wall can be hit when attempting to work with CountDown timers due to the Time associated type.

The embedded-time crate is attempting to homogenous the concept of time, clocks, durations and rates. At this point the various HALs have not adopted embedded-time, so this crate provides a simple macro to help accomodate drivers needing a consistent view of timers.

Usage

Generic drivers should be written in terms of CountDown that uses embedded-time flavors of time.

Application writers attempting to provision a concrete instance of the aforementioned drivers can use this macro to convert their HAL's timer into an embedded-time-centric CountDown.

Example

Use the embedded_countdown!(...) macro to define a new struct that can consume a HAL-specific timer, and wrap it into an embedded-time timer.

The macro takes a few arguments:

1. The name of the struct to create.
2. The exposed units (usually an embedded-time duration) expected by the driver.
3. The HAL's units expected by the built-in CountDown structure being wrapped.
4. The 1-argument conversion routine to handle the conversion.

embedded_countdown!(MsToHertzCountDown,
                embedded_time::duration::Milliseconds,
                stm32l4xx_hal::time::Hertz
                 => (ms) {
                        let hz: embedded_time::rate::Hertz = ms.to_rate().unwrap();
                        stm32l4xx_hal::time::Hertz(hz.0)
                } );

Once a structure has been defined, you can then use it:

let mut hal_hz_timer = Timer::tim16(device.TIM16, 1, clocks, &mut rcc.apb2);
let mut embedded_ms_timer = MsToHertzCountDown::from(hal_hz_timer);

Now the embedded_ms_timer is a CountDown<Time=embedded_time::duration::Milliseconds> and is no longer tied to a specific HAL implementation.