Add an example of using interrupt directly without async (#474)

examples/button_interrupt.rs

@@ -0,0 +1,60 @@
+//! Toggle an LED on/off with a button
+//!
+//! This assumes that a LED is connected to GPIO4.
+//! Additionally this assumes a button connected to GPIO9.
+//! On an ESP32C3 development board this is the BOOT button.
+//!
+//! Depending on your target and the board you are using you should change the pins.
+//! If your board doesn't have on-board LEDs don't forget to add an appropriate resistor.
+
+use core::num::NonZero;
+use esp_idf_hal::delay::FreeRtos;
+use esp_idf_hal::gpio::{InterruptType, PinDriver, Pull};
+use esp_idf_hal::peripherals::Peripherals;
+use esp_idf_hal::task::notification::Notification;
+
+fn main() -> anyhow::Result<()> {
+    esp_idf_hal::sys::link_patches();
+
+    let peripherals = Peripherals::take()?;
+    let mut led = PinDriver::output(peripherals.pins.gpio4)?;
+    let mut button = PinDriver::input(peripherals.pins.gpio9)?;
+
+    button.set_pull(Pull::Down)?;
+    button.set_interrupt_type(InterruptType::PosEdge)?;
+
+    let mut led_state = false;
+    led.set_low()?;
+
+    loop {
+        // prepare communication channel
+        let notification = Notification::new();
+        let waker = notification.notifier();
+
+        // register interrupt callback, here it's a closure on stack
+        unsafe {
+            button
+                .subscribe_nonstatic(move || {
+                    waker.notify(NonZero::new(1).unwrap());
+                })
+                .unwrap();
+        }
+
+        // enable interrupt, will be automatically disabled after being triggered
+        button.enable_interrupt()?;
+        // block until notified
+        notification.wait_any();
+
+        // toggle the LED
+        if led_state {
+            led.set_low()?;
+            led_state = false;
+        } else {
+            led.set_high()?;
+            led_state = true;
+        }
+
+        // debounce
+        FreeRtos::delay_ms(200);
+    }
+}