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Demonstrate FFT in example

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This commit is contained in:
Quentin Smith 2022-08-21 02:43:13 -04:00
parent ed97e61dbe
commit 64154fec8c
2 changed files with 24 additions and 1 deletions
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1
examples/nrf/Cargo.toml
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@ -32,3 +32,4 @@ embedded-storage = "0.3.0"
usbd-hid = "0.5.2"
serde = { version = "1.0.136", default-features = false }
num-integer = { version = "0.1.45", default-features = false }
microfft = "0.5.0"

24
examples/nrf/src/bin/pdm_continuous.rs
View File

@ -3,11 +3,13 @@
#![feature(type_alias_impl_trait)]
use defmt::info;
use core::cmp::Ordering;
use embassy_executor::Spawner;
use embassy_nrf::interrupt;
use embassy_nrf::pdm::{Config, Channels, Pdm, SamplerState, Frequency, Ratio};
use fixed::types::I7F1;
use num_integer::Roots;
use microfft::real::rfft_1024;
use {defmt_rtt as _, panic_probe as _};
// Demonstrates both continuous sampling and scanning multiple channels driven by a PPI linked timer
@ -36,8 +38,10 @@ async fn main(_p: Spawner) {
// 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;
let (peak_freq_index, peak_mag) = fft_peak_freq(&buf);
let peak_freq = peak_freq_index * 16000 / buf.len();
info!(
"{} samples, min {=i16}, max {=i16}, mean {=i16}, AC RMS {=i16}",
"{} samples, min {=i16}, max {=i16}, mean {=i16}, AC RMS {=i16}, peak {} @ {} Hz",
buf.len(),
buf.iter().min().unwrap(),
buf.iter().max().unwrap(),
@ -45,9 +49,27 @@ async fn main(_p: Spawner) {
(
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,
peak_mag, peak_freq,
);
SamplerState::Sampled
},
)
.await;
}
fn fft_peak_freq(input: &[i16; 1024]) -> (usize, u32) {
let mut f = [0f32; 1024];
for i in 0..input.len() {
f[i] = (input[i] as f32) / 32768.0;
}
// N.B. rfft_1024 does the FFT in-place so result is actually also a reference to f.
let result = rfft_1024(&mut f);
result[0].im = 0.0;
result
.iter()
.map(|c| ((c.norm_sqr()*32768.0) as u32).sqrt())
.enumerate()
.max_by(|(_, a), (_, b)| a.partial_cmp(b).unwrap_or(Ordering::Equal))
.unwrap()
}