From a14d24007ae6391121dc493782b900d6edb7d992 Mon Sep 17 00:00:00 2001 From: datdenkikniet Date: Sat, 22 Apr 2023 22:47:07 +0200 Subject: [PATCH] Update delay.md file to be a bit easier to read, and add spoiler tags for the walls of code --- book/en/src/by-example/delay.md | 58 ++++++++++++++++++++------------- 1 file changed, 36 insertions(+), 22 deletions(-) diff --git a/book/en/src/by-example/delay.md b/book/en/src/by-example/delay.md index f2863633ec..893ead9a03 100644 --- a/book/en/src/by-example/delay.md +++ b/book/en/src/by-example/delay.md @@ -1,18 +1,20 @@ # Tasks with delay -A convenient way to express *miniminal* timing requirements is by means of delaying progression. +A convenient way to express miniminal timing requirements is by delaying progression. -This can be achieved by instantiating a monotonic timer: +This can be achieved by instantiating a monotonic timer (for implementations, see [`rtic-monotonics`]): + +[`rtic-monotonics`]: https://github.com/rtic-rs/rtic/tree/master/rtic-monotonics +[`rtic-time`]: https://github.com/rtic-rs/rtic/tree/master/rtic-time ``` rust ... -rtic_monotonics::make_systick_handler!(); - #[init] fn init(cx: init::Context) -> (Shared, Local) { hprintln!("init"); - Systick::start(cx.core.SYST, 12_000_000); + let token = rtic_monotonics::create_systick_token!(); + Systick::start(cx.core.SYST, 12_000_000, token); ... ``` @@ -28,11 +30,14 @@ async fn foo(_cx: foo::Context) { ``` -Technically, the timer queue is implemented as a list based priority queue, where list-nodes are statically allocated as part of the underlying task `Future`. Thus, the timer queue is infallible at run-time (its size and allocation is determined at compile time). + + +Technically, the timer queue is implemented as a list based priority queue, where list-nodes are statically allocated as part of the underlying task `Future`. Thus, the timer queue is infallible at run-time (its size and allocation are determined at compile time). Similarly the channels implementation, the timer-queue implementation relies on a global *Critical Section* (CS) for race protection. For the examples a CS implementation is provided by adding `--features test-critical-section` to the build options. -For a complete example: +
+A complete example ``` rust {{#include ../../../../rtic/examples/async-delay.rs}} @@ -46,11 +51,15 @@ $ cargo run --target thumbv7m-none-eabi --example async-delay --features test-cr {{#include ../../../../rtic/ci/expected/async-delay.run}} ``` +
+ ## Timeout -Rust `Futures` (underlying Rust `async`/`await`) are composable. This makes it possible to `select` in between `Futures` that have completed. +Rust [`Future`]s (underlying Rust `async`/`await`) are composable. This makes it possible to `select` in between `Futures` that have completed. -A common use case is transactions with associated timeout. In the examples shown below, we introduce a fake HAL device which performs some transaction. We have modelled the time it takes based on the input parameter (`n`) as `350ms + n * 100ms)`. +[`Future`]: https://doc.rust-lang.org/std/future/trait.Future.html + +A common use case is transactions with an associated timeout. In the examples shown below, we introduce a fake HAL device that performs some transaction. We have modelled the time it takes based on the input parameter (`n`) as `350ms + n * 100ms`. Using the `select_biased` macro from the `futures` crate it may look like this: @@ -62,19 +71,13 @@ select_biased! { } ``` -Assuming the `hal_get` will take 450ms to finish, a short timeout of 200ms will expire. +Assuming the `hal_get` will take 450ms to finish, a short timeout of 200ms will expire before `hal_get` can complete. -``` rust -// Call hal with long relative timeout using `select_biased` -select_biased! { - v = hal_get(1).fuse() => hprintln!("hal returned {}", v), // hal finish first - _ = Systick::delay(1000.millis()).fuse() => hprintln!("timeout", ), -} -``` +Extending the timeout to 1000ms would cause `hal_get` will to complete first. -By extending the timeout to 1000ms, the `hal_get` will finish first. +Using `select_biased` any number of futures can be combined, so its very powerful. However, as the timeout pattern is frequently used, more ergonomic support is baked into RTIC, provided by the [`rtic-monotonics`] and [`rtic-time`] crates. -Using `select_biased` any number of futures can be combined, so its very powerful. However, as the timeout pattern is frequently used, it is directly supported by the RTIC [rtc-monotonics] and [rtic-time] crates. The second example from above using `timeout_after`: +Rewriting the second example from above using `timeout_after` gives: ``` rust // Call hal with long relative timeout using monotonic `timeout_after` @@ -84,7 +87,7 @@ match Systick::timeout_after(1000.millis(), hal_get(1)).await { } ``` -In cases you want exact control over time without drift. For this purpose we can use exact points in time using `Instance`, and spans of time using `Duration`. Operations on the `Instance` and `Duration` types are given by the [fugit] crate. +In cases where you want exact control over time without drift we can use exact points in time using `Instant`, and spans of time using `Duration`. Operations on the `Instant` and `Duration` types come from the [`fugit`] crate. [fugit]: https://crates.io/crates/fugit @@ -109,10 +112,20 @@ for n in 0..3 { } ``` -`instant = Systick::now()` gives the baseline (i.e., the absolute current point in time). We want to call `hal_get` after 1000ms relative to this absolute point in time. This can be accomplished by `Systick::delay_until(instant).await;`. We define the absolute point in time for the `timeout`, and call `Systick::timeout_at(timeout, hal_get(n)).await`. For the first loop iteration `n == 0`, and the `hal_get` will take 350ms (and finishes before the timeout). For the second iteration `n == 1`, and `hal_get` will take 450ms (and again succeeds to finish before the timeout). For the third iteration `n == 2` (`hal_get` will take 5500ms to finish). In this case we will run into a timeout. +`let mut instant = Systick::now()` sets the starting time of execution. +We want to call `hal_get` after 1000ms relative to this starting time. This can be accomplished by using `Systick::delay_until(instant).await`. -The complete example: +Then, we define a point in time called `timeout`, and call `Systick::timeout_at(timeout, hal_get(n)).await`. + +For the first iteration of the loop, with `n == 0`, the `hal_get` will take 350ms (and finishes before the timeout). + +For the second iteration, with `n == 1`, the `hal_get` will take 450ms (and again succeeds to finish before the timeout). + +For the third iteration, with `n == 2`, `hal_get` will take 550ms to finish, in which case we will run into a timeout. + +
+A complete example ``` rust {{#include ../../../../rtic/examples/async-timeout.rs}} @@ -125,3 +138,4 @@ $ cargo run --target thumbv7m-none-eabi --example async-timeout --features test- ``` console {{#include ../../../../rtic/ci/expected/async-timeout.run}} ``` +