61 lines
2.1 KiB
Text
61 lines
2.1 KiB
Text
|
= 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 link:https://crates.io/crates/embassy-time[embassy-time] crate. The types can be used with the internal
|
||
|
|
timer queue in link:https://crates.io/crates/embassy-executor[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:
|
||
|
|
|
||
|
|
[,rust]
|
||
|
|
----
|
||
|
|
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 link:https://docs.rs/embedded-hal/1.0.0/embedded_hal/delay/index.html[embedded-hal] and
|
||
|
|
link:https://docs.rs/embedded-hal-async/latest/embedded_hal_async/delay/index.html[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:
|
||
|
|
|
||
|
|
[,rust]
|
||
|
|
----
|
||
|
|
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;
|
||
|
|
}
|
||
|
|
----
|