Add multi-priority executor example.

README.md

@@ -18,7 +18,7 @@ The `embassy::executor` module provides an async/await executor based on [static
 - No `alloc`, no heap needed. Task futures are statically allocated.
 - Integrated timer queue allows simple sleeping: `Timer::after(Duration::from_ticks(64000)).await;`.
 - Suitable for low-power operation. Using interrupts or `WFE/SEV` ensures the CPU sleeps when there's no work to do. No busy-loop polling.
-- Creating multiple executor instances is supported, to run tasks with multiple priority levels. This allows higher-priority tasks to preempt lower-priority tasks. (example coming soon)
+- Creating multiple executor instances is supported, to run tasks with multiple priority levels. This allows higher-priority tasks to preempt lower-priority tasks.
 - Compatible with RTIC (example coming soon).
 
 ## Utils

examples/src/bin/multiprio.rs

@@ -0,0 +1,185 @@
+//! 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)]
+
+#[path = "../example_common.rs"]
+mod example_common;
+use example_common::*;
+
+use core::mem::MaybeUninit;
+use cortex_m_rt::entry;
+use embassy::executor::{task, Executor};
+use embassy::time::{Duration, Instant, Timer};
+use embassy_nrf::{interrupt, pac, rtc};
+use nrf52840_hal::clocks;
+
+#[task]
+async fn run_high() {
+    loop {
+        info!("        [high] tick!");
+        Timer::after(Duration::from_ticks(27374)).await;
+    }
+}
+
+#[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(32_000_000); // ~1 second
+
+        let end = Instant::now();
+        let ms = end.duration_since(start).into_ticks() / 33;
+        info!("    [med] done in {:u32} ms", ms);
+
+        Timer::after(Duration::from_ticks(23421)).await;
+    }
+}
+
+#[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(64_000_000); // ~2 seconds
+
+        let end = Instant::now();
+        let ms = end.duration_since(start).into_ticks() / 33;
+        info!("[low] done in {:u32} ms", ms);
+
+        Timer::after(Duration::from_ticks(32983)).await;
+    }
+}
+
+static mut RTC: MaybeUninit<rtc::RTC<pac::RTC1>> = MaybeUninit::uninit();
+static mut EXECUTOR_LOW: MaybeUninit<Executor<rtc::Alarm<pac::RTC1>>> = MaybeUninit::uninit();
+static mut EXECUTOR_MED: MaybeUninit<Executor<rtc::Alarm<pac::RTC1>>> = MaybeUninit::uninit();
+static mut EXECUTOR_HIGH: MaybeUninit<Executor<rtc::Alarm<pac::RTC1>>> = MaybeUninit::uninit();
+
+#[entry]
+fn main() -> ! {
+    info!("Hello World!");
+
+    let p = embassy_nrf::pac::Peripherals::take().dewrap();
+
+    clocks::Clocks::new(p.CLOCK)
+        .enable_ext_hfosc()
+        .set_lfclk_src_external(clocks::LfOscConfiguration::NoExternalNoBypass)
+        .start_lfclk();
+
+    let rtc: &'static _ = unsafe {
+        let ptr = RTC.as_mut_ptr();
+        ptr.write(rtc::RTC::new(p.RTC1));
+        &*ptr
+    };
+
+    rtc.start();
+    unsafe { embassy::time::set_clock(rtc) };
+
+    let executor_low: &'static _ = unsafe {
+        let ptr = EXECUTOR_LOW.as_mut_ptr();
+        ptr.write(Executor::new(rtc.alarm0(), cortex_m::asm::sev));
+        &*ptr
+    };
+
+    let executor_med: &'static _ = unsafe {
+        let ptr = EXECUTOR_MED.as_mut_ptr();
+        ptr.write(Executor::new(rtc.alarm1(), || {
+            interrupt::pend(interrupt::SWI0_EGU0)
+        }));
+        &*ptr
+    };
+
+    let executor_high: &'static _ = unsafe {
+        let ptr = EXECUTOR_HIGH.as_mut_ptr();
+        ptr.write(Executor::new(rtc.alarm2(), || {
+            interrupt::pend(interrupt::SWI1_EGU1)
+        }));
+        &*ptr
+    };
+
+    interrupt::set_priority(interrupt::SWI0_EGU0, interrupt::Priority::Level7);
+    interrupt::set_priority(interrupt::SWI1_EGU1, interrupt::Priority::Level6);
+    interrupt::enable(interrupt::SWI0_EGU0);
+    interrupt::enable(interrupt::SWI1_EGU1);
+
+    unsafe {
+        executor_low.spawn(run_low()).dewrap();
+        executor_med.spawn(run_med()).dewrap();
+        executor_high.spawn(run_high()).dewrap();
+
+        loop {
+            executor_low.run();
+            cortex_m::asm::wfe();
+        }
+    }
+}
+
+#[interrupt]
+unsafe fn SWI0_EGU0() {
+    EXECUTOR_MED.as_ptr().as_ref().unwrap().run()
+}
+
+#[interrupt]
+unsafe fn SWI1_EGU1() {
+    EXECUTOR_HIGH.as_ptr().as_ref().unwrap().run()
+}