add example of pin sharing between tasks

examples/rp/src/bin/blinky_two_tasks.rs

@@ -0,0 +1,61 @@
+#![no_std]
+#![no_main]
+/// This example demonstrates how to access a given pin from more than one embassy task
+/// The on-board LED is toggled by two tasks with slightly different periods, leading to the
+/// apparent duty cycle of the LED increasing, then decreasing, linearly. The phenomenon is similar
+/// to interference and the 'beats' you can hear if you play two frequencies close to one another
+/// [Link explaining it](https://www.physicsclassroom.com/class/sound/Lesson-3/Interference-and-Beats)
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_rp::{gpio, PeripheralRef};
+use embassy_sync::blocking_mutex::raw::ThreadModeRawMutex;
+use embassy_sync::mutex::Mutex;
+use embassy_time::Duration;
+use embassy_time::{Ticker, Timer};
+use gpio::{AnyPin, Level, Output};
+use {defmt_rtt as _, panic_probe as _};
+
+type LedType = Mutex<ThreadModeRawMutex, Option<PeripheralRef<'static, Output<'static, AnyPin>>>>;
+static LED: LedType = Mutex::new(None);
+
+#[embassy_executor::main]
+async fn main(spawner: Spawner) {
+    let p = embassy_rp::init(Default::default());
+    // set the content of the global LED reference to the real LED pin
+    let led = Output::new(AnyPin::from(p.PIN_25), Level::High);
+    // inner scope is so that once the mutex is written to, the MutexGuard is dropped, thus the
+    // Mutex is released
+    {
+        *(LED.lock().await) = Some(PeripheralRef::new(led));
+    }
+    let dt = 100 * 1_000_000;
+    let k = 1.003;
+
+    unwrap!(spawner.spawn(toggle(&LED, Duration::from_nanos(dt))));
+    unwrap!(spawner.spawn(toggle_slightly_slower(
+        &LED,
+        Duration::from_nanos((dt as f64 * k) as u64)
+    )));
+}
+
+async fn toggle_led(led: &'static LedType, delay: Duration) {
+    let mut ticker = Ticker::every(delay);
+    loop {
+        {
+            let mut led_unlocked = led.lock().await;
+            if let Some(pin_ref) = led_unlocked.as_mut() {
+                pin_ref.toggle();
+            }
+        }
+        ticker.next().await;
+    }
+}
+#[embassy_executor::task]
+async fn toggle(led: &'static LedType, delay: Duration) {
+    toggle_led(led, delay).await
+}
+
+#[embassy_executor::task]
+async fn toggle_slightly_slower(led: &'static LedType, delay: Duration) {
+    toggle_led(led, delay).await
+}