Add continuous PDM sampling with example

embassy-nrf/src/pdm.rs

@@ -115,6 +115,11 @@ impl<'d> Pdm<'d> {
             r.intenclr.write(|w| w.started().clear());
             WAKER.wake();
         }
+
+        if r.events_stopped.read().bits() != 0 {
+            r.intenclr.write(|w| w.stopped().clear());
+            WAKER.wake();
+        }
     }
 
     fn _set_gain(r: &pdm::RegisterBlock, gain_left: I7F1, gain_right: I7F1) {
@@ -141,15 +146,20 @@ impl<'d> Pdm<'d> {
         r.sample.ptr.write(|w| unsafe { w.sampleptr().bits(buf.as_mut_ptr() as u32) });
         r.sample.maxcnt.write(|w| unsafe { w.buffsize().bits(N as _) });
 
-        // Reset and enable the end event
+        // Reset and enable the events
         r.events_end.reset();
-        r.intenset.write(|w| w.end().set());
+        r.events_stopped.reset();
+        r.intenset.write(|w| {
+            w.end().set();
+            w.stopped().set();
+            w
+        });
 
         // Don't reorder the start event before the previous writes. Hopefully self
         // wouldn't happen anyway.
         compiler_fence(Ordering::SeqCst);
 
-        r.tasks_start.write(|w| { w.tasks_start().set_bit() });
+        r.tasks_start.write(|w| w.tasks_start().set_bit());
 
         // Wait for 'end' event.
         poll_fn(|cx| {
@@ -158,7 +168,109 @@ impl<'d> Pdm<'d> {
             WAKER.register(cx.waker());
 
             if r.events_end.read().bits() != 0 {
+                // END means the whole buffer has been received.
                 r.events_end.reset();
+                // Note that the beginning of the buffer might be overwritten before the task fully stops :(
+                r.tasks_stop.write(|w| w.tasks_stop().set_bit());
+            }
+
+            if r.events_stopped.read().bits() != 0 {
+                r.events_stopped.reset();
+                return Poll::Ready(());
+            }
+
+            Poll::Pending
+        })
+        .await;
+    }
+
+    /// Continuous sampling with double buffers.
+    ///
+    /// A TIMER and two PPI peripherals are passed in so that precise sampling
+    /// can be attained. The sampling interval is expressed by selecting a
+    /// timer clock frequency to use along with a counter threshold to be reached.
+    /// For example, 1KHz can be achieved using a frequency of 1MHz and a counter
+    /// threshold of 1000.
+    ///
+    /// A sampler closure is provided that receives the buffer of samples, noting
+    /// that the size of this buffer can be less than the original buffer's size.
+    /// A command is return from the closure that indicates whether the sampling
+    /// should continue or stop.
+    ///
+    /// NOTE: The time spent within the callback supplied should not exceed the time
+    /// taken to acquire the samples into a single buffer. You should measure the
+    /// time taken by the callback and set the sample buffer size accordingly.
+    /// Exceeding this time can lead to samples becoming dropped.
+    pub async fn run_task_sampler<S, const N: usize>(
+        &mut self,
+        bufs: &mut [[i16; N]; 2],
+        mut sampler: S,
+    ) where
+        S: FnMut(&[i16; N]) -> SamplerState,
+    {
+        let r = Self::regs();
+
+        r.sample.ptr.write(|w| unsafe { w.sampleptr().bits(bufs[0].as_mut_ptr() as u32) });
+        r.sample.maxcnt.write(|w| unsafe { w.buffsize().bits(N as _) });
+
+        // Reset and enable the events
+        r.events_end.reset();
+        r.events_started.reset();
+        r.events_stopped.reset();
+        r.intenset.write(|w| {
+            w.end().set();
+            w.started().set();
+            w.stopped().set();
+            w
+        });
+
+        // Don't reorder the start event before the previous writes. Hopefully self
+        // wouldn't happen anyway.
+        compiler_fence(Ordering::SeqCst);
+
+        r.tasks_start.write(|w| { w.tasks_start().set_bit() });
+
+        let mut current_buffer = 0;
+
+        let mut done = false;
+
+        // Wait for events and complete when the sampler indicates it has had enough.
+        poll_fn(|cx| {
+            let r = Self::regs();
+
+            WAKER.register(cx.waker());
+
+            if r.events_end.read().bits() != 0 {
+                compiler_fence(Ordering::SeqCst);
+
+                r.events_end.reset();
+                r.intenset.write(|w| w.end().set());
+
+                if !done { // Discard the last buffer after the user requested a stop.
+                    if sampler(&bufs[current_buffer]) == SamplerState::Sampled {
+                        let next_buffer = 1 - current_buffer;
+                        current_buffer = next_buffer;
+                    } else {
+                        r.tasks_stop.write(|w| w.tasks_stop().set_bit());
+                        done = true;
+                    };
+                };
+            }
+
+            if r.events_started.read().bits() != 0 {
+                r.events_started.reset();
+                r.intenset.write(|w| w.started().set());
+
+                let next_buffer = 1 - current_buffer;
+                r.sample
+                    .ptr
+                    .write(|w| unsafe { w.sampleptr().bits(bufs[next_buffer].as_mut_ptr() as u32) });
+            }
+
+            if r.events_stopped.read().bits() != 0 {
+                r.events_stopped.reset();
+                r.intenset.write(|w| w.stopped().set());
+
                 return Poll::Ready(());
             }
 

examples/nrf/src/bin/pdm.rs

@@ -25,7 +25,7 @@ async fn main(_p: Spawner) {
             pdm.set_gain(gain, gain);
             info!("Gain = {} dB", defmt::Debug2Format(&gain));
             for _ in 0..10 {
-                let mut buf = [0; 128];
+                let mut buf = [0; 1500];
                 pdm.sample(&mut buf).await;
                 info!(
                     "{} samples, min {=i16}, max {=i16}, RMS {=i16}",
@@ -36,6 +36,7 @@ async fn main(_p: Spawner) {
                         buf.iter().map(|v| i32::from(*v).pow(2)).fold(0i32, |a,b| a.saturating_add(b))
                     / buf.len() as i32).sqrt() as i16,
                 );
+                info!("samples = {}", &buf);
                 Timer::after(Duration::from_millis(100)).await;
             }
         }

examples/nrf/src/bin/pdm_continuous.rs

@@ -0,0 +1,50 @@
+#![no_std]
+#![no_main]
+#![feature(type_alias_impl_trait)]
+
+use defmt::info;
+use embassy_executor::Spawner;
+use embassy_nrf::interrupt;
+use embassy_nrf::pdm::{Config, Channels, Pdm, SamplerState};
+use embassy_nrf::timer::Frequency;
+use fixed::types::I7F1;
+use num_integer::Roots;
+use {defmt_rtt as _, panic_probe as _};
+
+// Demonstrates both continuous sampling and scanning multiple channels driven by a PPI linked timer
+
+#[embassy_executor::main]
+async fn main(_p: Spawner) {
+    let mut p = embassy_nrf::init(Default::default());
+    let mut config = Config::default();
+    // Pins are correct for the onboard microphone on the Feather nRF52840 Sense.
+    config.channels = Channels::Mono;
+    config.gain_left = I7F1::from_bits(5); // 2.5 dB
+    let mut pdm = Pdm::new(p.PDM, interrupt::take!(PDM), &mut p.P0_00, &mut p.P0_01, config);
+
+    let mut bufs = [[0; 500]; 2];
+
+    pdm
+        .run_task_sampler(
+            &mut bufs,
+            move |buf| {
+                // NOTE: It is important that the time spent within this callback
+                // does not exceed the time taken to acquire the 1500 samples we
+                // have in this example, which would be 10us + 2us per
+                // sample * 1500 = 18ms. You need to measure the time taken here
+                // and set the sample buffer size accordingly. Exceeding this
+                // time can lead to the peripheral re-writing the other buffer.
+                info!(
+                    "{} samples, min {=i16}, max {=i16}, RMS {=i16}",
+                    buf.len(),
+                    buf.iter().min().unwrap(),
+                    buf.iter().max().unwrap(),
+                    (
+                        buf.iter().map(|v| i32::from(*v).pow(2)).fold(0i32, |a,b| a.saturating_add(b))
+                    / buf.len() as i32).sqrt() as i16,
+                );
+                SamplerState::Sampled
+            },
+        )
+        .await;
+}