From ed97e61dbecc636c3cc9f67778d4b7eb48cff893 Mon Sep 17 00:00:00 2001
From: Quentin Smith <quentin@mit.edu>
Date: Sun, 21 Aug 2022 02:16:26 -0400
Subject: PDM clock frequency control

---
 examples/nrf/src/bin/pdm_continuous.rs | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

(limited to 'examples')

diff --git a/examples/nrf/src/bin/pdm_continuous.rs b/examples/nrf/src/bin/pdm_continuous.rs
index e7d1806bb..33ba1e274 100644
--- a/examples/nrf/src/bin/pdm_continuous.rs
+++ b/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::timer::Frequency;
+use embassy_nrf::pdm::{Config, Channels, Pdm, SamplerState, Frequency, Ratio};
 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
-- 
cgit