Time-keeping
In an embedded program, delaying a task is one of the most common actions taken. In an event loop, delays will need to be inserted to ensure that other tasks have a chance to run before the next iteration of the loop is called, if no other I/O is performed. Embassy provides abstractions to delay the current task for a specified interval of time.
The interface for time-keeping in Embassy is handled by the embassy-time crate. The types can be used with the internal timer queue in embassy-executor or a custom timer queue implementation.
Timer
The embassy::time::Timer
type provides two timing methods.
Timer::at
creates a future that completes at the specified Instant
, relative to the system boot time.
Timer::after
creates a future that completes after the specified Duration
, relative to when the future was created.
An example of a delay is provided as follows:
use embassy::executor::{task, Executor};
use embassy::time::{Duration, Timer};
#[task]
/// Task that ticks periodically
async fn tick_periodic() -> ! {
loop {
rprintln!("tick!");
// async sleep primitive, suspends the task for 500ms.
Timer::after(Duration::from_millis(500)).await;
}
}
Delay
The embassy::time::Delay
type provides an implementation of the embedded-hal and
embedded-hal-async traits. This can be used for drivers
that expect a generic delay implementation to be provided.
An example of how this can be used:
use embassy::executor::{task, Executor};
#[task]
/// Task that ticks periodically
async fn tick_periodic() -> ! {
loop {
rprintln!("tick!");
// async sleep primitive, suspends the task for 500ms.
generic_delay(embassy::time::Delay).await
}
}
async fn generic_delay<D: embedded_hal_async::delay::DelayNs>(delay: D) {
delay.delay_ms(500).await;
}