Struct Pit

pub struct Pit<'a, const R: u16> { /* private fields */ }

Timer based on 8253 “PIT” hardware

Although the PIT contains an internal counter, it is not a suitable source of ticks because it runs at a high, fixed frequency and wraps very quickly. So instead, we configure the PIT to generate periodic interrupts, and we increment an in-memory counter each time an interrupt fires.

Parameter R is the reload value to use. This is loaded into a hardware register and determines the interrupt frequency. Use reload_value to compute a reload value for the desired frequency.

Implementations

impl<const R: u16> Pit<'_, R>

pub unsafe fn new() -> Self

Creates a new PIT timer object.

Safety

There must never be more than a single instance of Pit alive at any given time.

pub fn start(&self)

Configures the PIT to start generating periodic interrupts.

pub fn handle_interrupt(&self)

Handler to call when a PIT interrupt occurs.

This will increment the internal in-memory timer and dispatch any alarms.

Trait Implementations

impl<'a, const R: u16> Alarm<'a> for Pit<'a, R>

fn set_alarm_client(&self, client: &'a dyn AlarmClient)

Specify the callback for when the counter reaches the alarm value. If there was a previously installed callback this call replaces it.

fn set_alarm(&self, reference: Self::Ticks, dt: Self::Ticks)

Specify when the callback should be called and enable it. The callback will be enqueued when Time::now() == reference + dt. The callback itself may not run exactly at this time, due to delays. However, it it assured to execute after reference + dt: it can be delayed but will never fire early. The method takes reference and dt rather than a single value denoting the counter value so it can distinguish between alarms which have very recently already passed and those in the far far future (see #1651).

fn get_alarm(&self) -> Self::Ticks

Return the current alarm value. This is undefined at boot and otherwise returns now + dt from the last call to set_alarm.

fn disarm(&self) -> Result<(), ErrorCode>

Disable the alarm and stop it from firing in the future. Valid Result<(), ErrorCode> codes are:

fn is_armed(&self) -> bool

Returns whether the alarm is currently armed. Note that this does not reliably indicate whether there will be a future callback: it is possible that the alarm has triggered (and disarmed) and a callback is pending and has not been called yet. In this case it possible for is_armed to return false yet to receive a callback.

fn minimum_dt(&self) -> Self::Ticks

Return the minimum dt value that is supported. Any dt smaller than this will automatically be increased to this minimum value.

impl<const R: u16> Time for Pit<'_, R>

type Frequency = PitFreq<R>

The number of ticks per second

type Ticks = Ticks32

The width of a time value

fn now(&self) -> Self::Ticks

Returns a timestamp. Depending on the implementation of Time, this could represent either a static timestamp or a sample of a counter; if an implementation relies on it being constant or changing it should use Timestamp or Counter.