rp: Add raw interrupt handler example

examples/rp/Cargo.toml

@@ -27,6 +27,7 @@ fixed-macro = "1.2"
 #cortex-m = { version = "0.7.6", features = ["critical-section-single-core"] }
 cortex-m = { version = "0.7.6", features = ["inline-asm"] }
 cortex-m-rt = "0.7.0"
+critical-section = "1.1"
 panic-probe = { version = "0.3", features = ["print-defmt"] }
 display-interface-spi = "0.4.1"
 embedded-graphics = "0.7.1"

examples/rp/src/bin/interrupt.rs

@@ -0,0 +1,95 @@
+//! This example shows how you can use raw interrupt handlers alongside embassy.
+//! The example also showcases some of the options available for sharing resources/data.
+//!
+//! In the example, an ADC reading is triggered every time the PWM wraps around.
+//! The sample data is sent down a channel, to be processed inside a low priority task.
+//! The processed data is then used to adjust the PWM duty cycle, once every second.
+
+#![no_std]
+#![no_main]
+
+use core::cell::{Cell, RefCell};
+
+use defmt::*;
+use embassy_executor::Spawner;
+use embassy_rp::adc::{self, Adc, Blocking};
+use embassy_rp::interrupt;
+use embassy_rp::pwm::{Config, Pwm};
+use embassy_rp::{gpio::Pull, peripherals::PWM_SLICE4};
+use embassy_sync::{
+    blocking_mutex::{raw::CriticalSectionRawMutex, Mutex},
+    channel::Channel,
+};
+use embassy_time::{Duration, Ticker};
+use portable_atomic::{AtomicU32, Ordering};
+use static_cell::StaticCell;
+use {defmt_rtt as _, panic_probe as _};
+
+static COUNTER: AtomicU32 = AtomicU32::new(0);
+static PWM: Mutex<CriticalSectionRawMutex, RefCell<Option<Pwm<PWM_SLICE4>>>> = Mutex::new(RefCell::new(None));
+static ADC: Mutex<CriticalSectionRawMutex, RefCell<Option<(Adc<Blocking>, adc::Channel)>>> =
+    Mutex::new(RefCell::new(None));
+static ADC_VALUES: Channel<CriticalSectionRawMutex, u16, 2048> = Channel::new();
+
+#[embassy_executor::main]
+async fn main(spawner: Spawner) {
+    embassy_rp::pac::SIO.spinlock(31).write_value(1);
+    let p = embassy_rp::init(Default::default());
+
+    let adc = Adc::new_blocking(p.ADC, Default::default());
+    let p26 = adc::Channel::new_pin(p.PIN_26, Pull::None);
+    ADC.lock(|a| a.borrow_mut().replace((adc, p26)));
+
+    let pwm = Pwm::new_output_b(p.PWM_SLICE4, p.PIN_25, Default::default());
+    PWM.lock(|p| p.borrow_mut().replace(pwm));
+
+    // Enable the interrupt for pwm slice 4
+    embassy_rp::pac::PWM.inte().modify(|w| w.set_ch4(true));
+    unsafe {
+        cortex_m::peripheral::NVIC::unmask(interrupt::PWM_IRQ_WRAP);
+    }
+
+    // Tasks require their resources to have 'static lifetime
+    // No Mutex needed when sharing within the same executor/prio level
+    static AVG: StaticCell<Cell<u32>> = StaticCell::new();
+    let avg = AVG.init(Default::default());
+    spawner.must_spawn(processing(avg));
+
+    let mut ticker = Ticker::every(Duration::from_secs(1));
+    loop {
+        ticker.next().await;
+        let freq = COUNTER.swap(0, Ordering::Relaxed);
+        info!("pwm freq: {:?} Hz", freq);
+        info!("adc average: {:?}", avg.get());
+
+        // Update the pwm duty cycle, based on the averaged adc reading
+        let mut config = Config::default();
+        config.compare_b = ((avg.get() as f32 / 4095.0) * config.top as f32) as _;
+        PWM.lock(|p| p.borrow_mut().as_mut().unwrap().set_config(&config));
+    }
+}
+
+#[embassy_executor::task]
+async fn processing(avg: &'static Cell<u32>) {
+    let mut buffer: heapless::HistoryBuffer<u16, 100> = Default::default();
+    loop {
+        let val = ADC_VALUES.receive().await;
+        buffer.write(val);
+        let sum: u32 = buffer.iter().map(|x| *x as u32).sum();
+        avg.set(sum / buffer.len() as u32);
+    }
+}
+
+#[interrupt]
+fn PWM_IRQ_WRAP() {
+    critical_section::with(|cs| {
+        let mut adc = ADC.borrow(cs).borrow_mut();
+        let (adc, p26) = adc.as_mut().unwrap();
+        let val = adc.blocking_read(p26).unwrap();
+        ADC_VALUES.try_send(val).ok();
+
+        // Clear the interrupt, so we don't immediately re-enter this irq handler
+        PWM.borrow(cs).borrow_mut().as_mut().unwrap().clear_wrapped();
+    });
+    COUNTER.fetch_add(1, Ordering::Relaxed);
+}