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book/example polish
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2 changed files with 28 additions and 25 deletions
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@ -6,13 +6,14 @@ This can be achieved by instantiating a monotonic timer:
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``` rust
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...
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rtic_monotonics::make_systick_timer_queue!(TIMER);
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rtic_monotonics::make_systick_handler!();
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#[init]
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fn init(cx: init::Context) -> (Shared, Local) {
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let systick = Systick::start(cx.core.SYST, 12_000_000);
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TIMER.initialize(systick);
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...
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fn init(cx: init::Context) -> (Shared, Local) {
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hprintln!("init");
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Systick::start(cx.core.SYST, 12_000_000);
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...
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```
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A *software* task can `await` the delay to expire:
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@ -21,8 +22,10 @@ A *software* task can `await` the delay to expire:
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#[task]
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async fn foo(_cx: foo::Context) {
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...
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TIMER.delay(100.millis()).await;
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Systick::delay(100.millis()).await;
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...
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}
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```
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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).
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@ -51,21 +54,21 @@ A common use case is transactions with associated timeout. In the examples shown
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Using the `select_biased` macro from the `futures` crate it may look like this:
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```rust
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``` rust
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// Call hal with short relative timeout using `select_biased`
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select_biased! {
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v = hal_get(&TIMER, 1).fuse() => hprintln!("hal returned {}", v),
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_ = TIMER.delay(200.millis()).fuse() => hprintln!("timeout", ), // this will finish first
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v = hal_get(1).fuse() => hprintln!("hal returned {}", v),
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_ = Systick::delay(200.millis()).fuse() => hprintln!("timeout", ), // this will finish first
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}
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```
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Assuming the `hal_get` will take 450ms to finish, a short timeout of 200ms will expire.
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```rust
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``` rust
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// Call hal with long relative timeout using `select_biased`
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select_biased! {
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v = hal_get(&TIMER, 1).fuse() => hprintln!("hal returned {}", v), // hal finish first
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_ = TIMER.delay(1000.millis()).fuse() => hprintln!("timeout", ),
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v = hal_get(1).fuse() => hprintln!("hal returned {}", v), // hal finish first
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_ = Systick::delay(1000.millis()).fuse() => hprintln!("timeout", ),
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}
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```
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@ -73,9 +76,9 @@ By extending the timeout to 1000ms, the `hal_get` will finish first.
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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`:
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```rust
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``` rust
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// Call hal with long relative timeout using monotonic `timeout_after`
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match TIMER.timeout_after(1000.millis(), hal_get(&TIMER, 1)).await {
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match Systick::timeout_after(1000.millis(), hal_get(1)).await {
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Ok(v) => hprintln!("hal returned {}", v),
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_ => hprintln!("timeout"),
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}
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@ -85,28 +88,28 @@ In cases you want exact control over time without drift. For this purpose we can
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[fugit]: https://crates.io/crates/fugit
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```rust
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``` rust
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// get the current time instance
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let mut instant = TIMER.now();
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let mut instant = Systick::now();
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// do this 3 times
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for n in 0..3 {
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// exact point in time without drift
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// absolute point in time without drift
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instant += 1000.millis();
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TIMER.delay_until(instant).await;
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Systick::delay_until(instant).await;
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// exact point it time for timeout
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// absolute point it time for timeout
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let timeout = instant + 500.millis();
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hprintln!("now is {:?}, timeout at {:?}", TIMER.now(), timeout);
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hprintln!("now is {:?}, timeout at {:?}", Systick::now(), timeout);
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match TIMER.timeout_at(timeout, hal_get(&TIMER, n)).await {
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Ok(v) => hprintln!("hal returned {} at time {:?}", v, TIMER.now()),
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match Systick::timeout_at(timeout, hal_get(n)).await {
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Ok(v) => hprintln!("hal returned {} at time {:?}", v, Systick::now()),
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_ => hprintln!("timeout"),
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}
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}
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```
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`instant = TIMER.now()` gives the baseline (i.e., the exact current point in time). We want to call `hal_get` after 1000ms relative to this exact point in time. This can be accomplished by `TIMER.delay_until(instant).await;`. We define the absolute point in time for the `timeout`, and call `TIMER.timeout_at(timeout, hal_get(&TIMER, 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.
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`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.
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The complete example:
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@ -61,11 +61,11 @@ mod app {
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// do this 3 times
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for n in 0..3 {
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// exact point in time without drift
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// absolute point in time without drift
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instant += 1000.millis();
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Systick::delay_until(instant).await;
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// exact point it time for timeout
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// absolute point it time for timeout
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let timeout = instant + 500.millis();
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hprintln!("now is {:?}, timeout at {:?}", Systick::now(), timeout);
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