60 lines
2.1 KiB
Text
60 lines
2.1 KiB
Text
= Time-keeping
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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
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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
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to delay the current task for a specified interval of time.
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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
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timer queue in link:https://crates.io/crates/embassy-executor[embassy-executor] or a custom timer queue implementation.
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== Timer
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The `embassy::time::Timer` type provides two timing methods.
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`Timer::at` creates a future that completes at the specified `Instant`, relative to the system boot time.
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`Timer::after` creates a future that completes after the specified `Duration`, relative to when the future was created.
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An example of a delay is provided as follows:
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[,rust]
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----
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use embassy::executor::{task, Executor};
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use embassy::time::{Duration, Timer};
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#[task]
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/// Task that ticks periodically
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async fn tick_periodic() -> ! {
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loop {
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rprintln!("tick!");
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// async sleep primitive, suspends the task for 500ms.
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Timer::after(Duration::from_millis(500)).await;
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}
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}
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----
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== Delay
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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
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link:https://docs.rs/embedded-hal-async/latest/embedded_hal_async/delay/index.html[embedded-hal-async] traits. This can be used for drivers
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that expect a generic delay implementation to be provided.
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An example of how this can be used:
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[,rust]
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----
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use embassy::executor::{task, Executor};
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#[task]
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/// Task that ticks periodically
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async fn tick_periodic() -> ! {
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loop {
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rprintln!("tick!");
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// async sleep primitive, suspends the task for 500ms.
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generic_delay(embassy::time::Delay).await
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}
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}
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async fn generic_delay<D: embedded_hal_async::delay::DelayNs>(delay: D) {
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delay.delay_ms(500).await;
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}
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----
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