Drift free timing examples

CHANGELOG.md

@@ -8,6 +8,8 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 
 - CI changelog entry enforcer
+- `examples/periodic-at.rs`, an example of a periodic timer without accumulated drift.
+- `examples/periodic-at2.rs`, an example of a periodic process with two tasks, with offset timing. Here we depict two alternative usages of the timer type, explicit and trait based.
 
 ## [v1.0.0] - 2021-12-25
 

ci/expected/periodic-at.run

@@ -0,0 +1,4 @@
+foo Instant { ticks: 0 }
+foo Instant { ticks: 100 }
+foo Instant { ticks: 200 }
+foo Instant { ticks: 300 }

ci/expected/periodic-at2.run

@@ -0,0 +1,7 @@
+foo Instant { ticks: 0 }
+bar Instant { ticks: 10 }
+foo Instant { ticks: 110 }
+bar Instant { ticks: 120 }
+foo Instant { ticks: 220 }
+bar Instant { ticks: 230 }
+foo Instant { ticks: 330 }

examples/periodic-at.rs

@@ -0,0 +1,49 @@
+//! examples/periodic-at.rs
+
+#![deny(unsafe_code)]
+#![deny(warnings)]
+#![no_main]
+#![no_std]
+
+use panic_semihosting as _;
+
+#[rtic::app(device = lm3s6965, dispatchers = [SSI0])]
+mod app {
+    use cortex_m_semihosting::{debug, hprintln};
+    use systick_monotonic::*;
+
+    #[monotonic(binds = SysTick, default = true)]
+    type MyMono = Systick<100>; // 100 Hz / 10 ms granularity
+
+    #[shared]
+    struct Shared {}
+
+    #[local]
+    struct Local {}
+
+    #[init]
+    fn init(cx: init::Context) -> (Shared, Local, init::Monotonics) {
+        let systick = cx.core.SYST;
+
+        // Initialize the monotonic (SysTick rate in QEMU is 12 MHz)
+        let mut mono = Systick::new(systick, 12_000_000);
+
+        foo::spawn_after(1.secs(), mono.now()).unwrap();
+
+        (Shared {}, Local {}, init::Monotonics(mono))
+    }
+
+    #[task(local = [cnt: u32 = 0])]
+    fn foo(cx: foo::Context, instant: fugit::TimerInstantU64<100>) {
+        hprintln!("foo {:?}", instant).ok();
+        *cx.local.cnt += 1;
+
+        if *cx.local.cnt == 4 {
+            debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
+        }
+
+        // Periodic ever 1 seconds
+        let next_instant = instant + 1.secs();
+        foo::spawn_at(next_instant, next_instant).unwrap();
+    }
+}

examples/periodic-at2.rs

@@ -0,0 +1,61 @@
+//! examples/periodic-at2.rs
+
+#![deny(unsafe_code)]
+#![deny(warnings)]
+#![no_main]
+#![no_std]
+
+use panic_semihosting as _;
+
+#[rtic::app(device = lm3s6965, dispatchers = [SSI0])]
+mod app {
+    use cortex_m_semihosting::{debug, hprintln};
+    use systick_monotonic::*;
+
+    #[monotonic(binds = SysTick, default = true)]
+    type MyMono = Systick<100>; // 100 Hz / 10 ms granularity
+
+    #[shared]
+    struct Shared {}
+
+    #[local]
+    struct Local {}
+
+    #[init]
+    fn init(cx: init::Context) -> (Shared, Local, init::Monotonics) {
+        let systick = cx.core.SYST;
+
+        // Initialize the monotonic (SysTick rate in QEMU is 12 MHz)
+        let mut mono = Systick::new(systick, 12_000_000);
+
+        foo::spawn_after(1.secs(), mono.now()).unwrap();
+
+        (Shared {}, Local {}, init::Monotonics(mono))
+    }
+
+    // Using the explicit type of the timer implementation
+    #[task(local = [cnt: u32 = 0])]
+    fn foo(cx: foo::Context, instant: fugit::TimerInstantU64<100>) {
+        hprintln!("foo {:?}", instant).ok();
+        *cx.local.cnt += 1;
+
+        if *cx.local.cnt == 4 {
+            debug::exit(debug::EXIT_SUCCESS); // Exit QEMU simulator
+        }
+
+        // Spawn a new message with 100 ms offset to spawned time
+        let next_instant = instant + 100.millis();
+        bar::spawn_at(next_instant, next_instant).unwrap();
+    }
+
+    // Using the Instant from the Monotonic trait
+    // This remains agnostic to the timer implementation
+    #[task(local = [cnt: u32 = 0])]
+    fn bar(_cx: bar::Context, instant: <MyMono as rtic_monotonic::Monotonic>::Instant) {
+        hprintln!("bar {:?}", instant).ok();
+
+        // Spawn a new message with 1s offset to spawned time
+        let next_instant = instant + 1.secs();
+        foo::spawn_at(next_instant, next_instant).unwrap();
+    }
+}