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= 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:
TIP: Dependencies needed to run this example link:#_the_cargo_toml[can be found here].
[,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:
TIP: Dependencies needed to run this example link:#_the_cargo_toml[can be found here].
[,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;
}
----
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