added priority based example

examples/stm32f0/src/bin/priority.rs

@@ -0,0 +1,139 @@
+//! This example showcases how to create multiple Executor instances to run tasks at
+//! different priority levels.
+//!
+//! Low priority executor runs in thread mode (not interrupt), and uses `sev` for signaling
+//! there's work in the queue, and `wfe` for waiting for work.
+//!
+//! Medium and high priority executors run in two interrupts with different priorities.
+//! Signaling work is done by pending the interrupt. No "waiting" needs to be done explicitly, since
+//! when there's work the interrupt will trigger and run the executor.
+//!
+//! Sample output below. Note that high priority ticks can interrupt everything else, and
+//! medium priority computations can interrupt low priority computations, making them to appear
+//! to take significantly longer time.
+//!
+//! ```not_rust
+//!     [med] Starting long computation
+//!     [med] done in 992 ms
+//!         [high] tick!
+//! [low] Starting long computation
+//!     [med] Starting long computation
+//!         [high] tick!
+//!         [high] tick!
+//!     [med] done in 993 ms
+//!     [med] Starting long computation
+//!         [high] tick!
+//!         [high] tick!
+//!     [med] done in 993 ms
+//! [low] done in 3972 ms
+//!     [med] Starting long computation
+//!         [high] tick!
+//!         [high] tick!
+//!     [med] done in 993 ms
+//! ```
+//!
+//! For comparison, try changing the code so all 3 tasks get spawned on the low priority executor.
+//! You will get an output like the following. Note that no computation is ever interrupted.
+//!
+//! ```not_rust
+//!         [high] tick!
+//!     [med] Starting long computation
+//!     [med] done in 496 ms
+//! [low] Starting long computation
+//! [low] done in 992 ms
+//!     [med] Starting long computation
+//!     [med] done in 496 ms
+//!         [high] tick!
+//! [low] Starting long computation
+//! [low] done in 992 ms
+//!         [high] tick!
+//!     [med] Starting long computation
+//!     [med] done in 496 ms
+//!         [high] tick!
+//! ```
+//!
+
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use cortex_m_rt::entry;
+use defmt::*;
+use embassy_stm32::executor::{Executor, InterruptExecutor};
+use embassy_stm32::interrupt;
+use embassy_stm32::interrupt::InterruptExt;
+use embassy_time::{Duration, Instant, Timer};
+use static_cell::StaticCell;
+use {defmt_rtt as _, panic_probe as _};
+
+#[embassy_executor::task]
+async fn run_high() {
+    loop {
+        // info!("        [high] tick!");
+        Timer::after(Duration::from_ticks(27374)).await;
+    }
+}
+
+#[embassy_executor::task]
+async fn run_med() {
+    loop {
+        let start = Instant::now();
+        info!("    [med] Starting long computation");
+
+        // Spin-wait to simulate a long CPU computation
+        cortex_m::asm::delay(8_000_000); // ~1 second
+
+        let end = Instant::now();
+        let ms = end.duration_since(start).as_ticks() / 33;
+        info!("    [med] done in {} ms", ms);
+
+        Timer::after(Duration::from_ticks(23421)).await;
+    }
+}
+
+#[embassy_executor::task]
+async fn run_low() {
+    loop {
+        let start = Instant::now();
+        info!("[low] Starting long computation");
+
+        // Spin-wait to simulate a long CPU computation
+        cortex_m::asm::delay(16_000_000); // ~2 seconds
+
+        let end = Instant::now();
+        let ms = end.duration_since(start).as_ticks() / 33;
+        info!("[low] done in {} ms", ms);
+
+        Timer::after(Duration::from_ticks(32983)).await;
+    }
+}
+
+static EXECUTOR_HIGH: StaticCell<InterruptExecutor<interrupt::USART1>> = StaticCell::new();
+static EXECUTOR_MED: StaticCell<InterruptExecutor<interrupt::USART2>> = StaticCell::new();
+static EXECUTOR_LOW: StaticCell<Executor> = StaticCell::new();
+
+#[entry]
+fn main() -> ! {
+    // Initialize and create handle for devicer peripherals
+    let _p = embassy_stm32::init(Default::default());
+
+    // High-priority executor: USART1, priority level 6
+    let irq = interrupt::take!(USART1);
+    irq.set_priority(interrupt::Priority::P6);
+    let executor = EXECUTOR_HIGH.init(InterruptExecutor::new(irq));
+    let spawner = executor.start();
+    unwrap!(spawner.spawn(run_high()));
+
+    // Medium-priority executor: USART2, priority level 7
+    let irq = interrupt::take!(USART2);
+    irq.set_priority(interrupt::Priority::P7);
+    let executor = EXECUTOR_MED.init(InterruptExecutor::new(irq));
+    let spawner = executor.start();
+    unwrap!(spawner.spawn(run_med()));
+
+    // Low priority executor: runs in thread mode, using WFE/SEV
+    let executor = EXECUTOR_LOW.init(Executor::new());
+    executor.run(|spawner| {
+        unwrap!(spawner.spawn(run_low()));
+    });
+}