PDM clock frequency control

embassy-nrf/src/pdm.rs

@@ -9,6 +9,8 @@ use embassy_util::waitqueue::AtomicWaker;
 use futures::future::poll_fn;
 use pac::{pdm, PDM};
 use pdm::mode::{EDGE_A, OPERATION_A};
+pub use pdm::pdmclkctrl::FREQ_A as Frequency;
+pub use pdm::ratio::RATIO_A as Ratio;
 use fixed::types::I7F1;
 
 use crate::interrupt::InterruptExt;
@@ -32,8 +34,10 @@ static WAKER: AtomicWaker = AtomicWaker::new();
 /// See the `Default` impl for suitable default values.
 #[non_exhaustive]
 pub struct Config {
-    /// Clock
+    /// Clock frequency
+    pub frequency: Frequency,
     /// Clock ratio
+    pub ratio: Ratio,
     /// Channels
     pub channels: Channels,
     /// Edge to sample on
@@ -48,6 +52,8 @@ impl Default for Config {
     /// Default configuration for single channel sampling.
     fn default() -> Self {
         Self {
+            frequency: Frequency::DEFAULT,
+            ratio: Ratio::RATIO80,
             channels: Channels::Stereo,
             left_edge: Edge::FallingEdge,
             gain_left: I7F1::ZERO,
@@ -78,11 +84,12 @@ impl<'d> Pdm<'d> {
 
         let r = unsafe { &*PDM::ptr() };
 
-        let Config { channels, left_edge, gain_left, gain_right } = config;
+        let Config { frequency, ratio, channels, left_edge, gain_left, gain_right } = config;
 
         // Configure channels
         r.enable.write(|w| w.enable().enabled());
-        // TODO: Clock control
+        r.pdmclkctrl.write(|w| w.freq().variant(frequency));
+        r.ratio.write(|w| w.ratio().variant(ratio));
         r.mode.write(|w| {
             w.operation().variant(channels.into());
             w.edge().variant(left_edge.into());

examples/nrf/src/bin/pdm_continuous.rs

@@ -5,8 +5,7 @@
 use defmt::info;
 use embassy_executor::Spawner;
 use embassy_nrf::interrupt;
-use embassy_nrf::pdm::{Config, Channels, Pdm, SamplerState};
+use embassy_nrf::pdm::{Config, Channels, Pdm, SamplerState, Frequency, Ratio};
-use embassy_nrf::timer::Frequency;
 use fixed::types::I7F1;
 use num_integer::Roots;
 use {defmt_rtt as _, panic_probe as _};
@@ -18,11 +17,13 @@ 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.frequency = Frequency::_1280K; // 16 kHz sample rate
+    config.ratio = Ratio::RATIO80;
     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];
+    let mut bufs = [[0; 1024]; 2];
 
     pdm
         .run_task_sampler(
@@ -34,13 +35,15 @@ async fn main(_p: Spawner) {
                 // 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.
+                let mean = (buf.iter().map(|v| i32::from(*v)).sum::<i32>() / buf.len() as i32) as i16;
                 info!(
-                    "{} samples, min {=i16}, max {=i16}, RMS {=i16}",
+                    "{} samples, min {=i16}, max {=i16}, mean {=i16}, AC RMS {=i16}",
                     buf.len(),
                     buf.iter().min().unwrap(),
                     buf.iter().max().unwrap(),
+                    mean,
                     (
-                        buf.iter().map(|v| i32::from(*v).pow(2)).fold(0i32, |a,b| a.saturating_add(b))
+                        buf.iter().map(|v| i32::from(*v - mean).pow(2)).fold(0i32, |a,b| a.saturating_add(b))
                     / buf.len() as i32).sqrt() as i16,
                 );
                 SamplerState::Sampled