Struct cortex_m_systick_countdown::PollingSysTick

pub struct PollingSysTick { /* fields omitted */ }

Millisecond counter based on SysTick

Effectively a singleton because this struct will consume the only SYST value in the program. (Use free if you need to get it back.)

Usage

For simple blocking delays, use the embedded_hal::blocking::delay::DelayMs trait to pause the program for a certain amount of time.

For timeouts or other non-blocking operations, create a MillisCountDown instance and use its start and wait methods. You can have multiple MillisCountDown instances active at the same time.

Because this uses polling for measuring SysTick, it will work even during periods where interrupts are disabled.

Implementation

We configure SysTick’s reload value to a count that will take 1ms to decrement to. When we detect that this count has wrapped over we increment our internal count of the milliseconds that have ellapsed.

We use the polling pattern for querying the time, rather than relying on interrupts, which means that our count is only guaranteed to be no faster than SysTick. We only keep accurate count while the count method is being actively called, and may experience some jitter depending on where SysTick is in its count when you start a timer.

This also means we need to use internal mutability so that we can access the SYST.has_wrapped() method (which mutates on read) and update our counter.

Methods

impl PollingSysTick

pub fn new(syst: SYST, calibration: &SysTickCalibration) -> Self

Configures SysTick based on the values provided in the calibration.

pub fn free(self) -> SYST

Turns this value back into the underlying SysTick.

Trait Implementations

impl CountsMillis for PollingSysTick

fn count(&self) -> Wrapping<u32>

Returns a number that goes up no faster than once per millisecond. This value will not increment unless polled (this is so it can operate during critical sections when interrupts are disabled).

impl DelayMs<u32> for PollingSysTick

fn delay_ms(&mut self, ms: u32)

Pauses execution for ms milliseconds