Add a lighter downsampler option

Cargo.toml

@@ -178,6 +178,9 @@ esp32s3 = [
     "esp-wifi/esp32s3",
 ]
 
+# Signal processing
+downsampler-light = [] # uses IIR-based filtering and less memory
+
 # Print options
 uart = ["esp-backtrace/print-uart", "esp-println/uart"]
 jtag_serial = ["esp-backtrace/print-jtag-serial", "esp-println/jtag_serial"]

src/board/wifi/mod.rs

@@ -20,7 +20,6 @@ use crate::{
 use alloc::{boxed::Box, rc::Rc};
 use embassy_executor::Spawner;
 use embassy_net::{Config, Stack, StackResources};
-use embassy_time::{Duration, Timer as DelayTimer};
 use esp_wifi::{
     wifi::{WifiApDevice, WifiDevice, WifiDeviceMode, WifiStaDevice},
     EspWifiInitFor, EspWifiInitialization,

src/states/measure.rs

@@ -22,7 +22,6 @@ use object_chain::{chain, Chain, ChainElement, Link};
 use signal_processing::{
     compressing_buffer::CompressingBuffer,
     filter::{
-        downsample::DownSampler,
         iir::{precomputed::ALL_PASS, HighPass, Iir, LowPass},
         pli::{adaptation_blocking::AdaptationBlocking, PowerLineFilter},
         Filter,
@@ -31,6 +30,9 @@ use signal_processing::{
     moving::sum::EstimatedSum,
 };
 
+#[cfg(not(feature = "downsampler-light"))]
+use signal_processing::filter::downsample::DownSampler;
+
 type MessageQueue = Channel<CriticalSectionRawMutex, Sample, 32>;
 
 // FIXME: avoid this allow
@@ -48,13 +50,66 @@ pub type EcgFilter = chain! {
     Iir<'static, HighPass, 2>
 };
 
+#[cfg(feature = "downsampler-light")]
+pub struct DownsamplerLight {
+    filter: Iir<'static, LowPass, 2>,
+    counter: u8,
+}
+
+#[cfg(feature = "downsampler-light")]
+impl Filter for DownsamplerLight {
+    fn clear(&mut self) {
+        self.filter.clear();
+        self.counter = 0;
+    }
+
+    fn update(&mut self, sample: f32) -> Option<f32> {
+        let filtered = self.filter.update(sample)?;
+        if self.counter == 0 {
+            self.counter = 7;
+            Some(filtered)
+        } else {
+            self.counter -= 1;
+            None
+        }
+    }
+}
+
 // Downsample by 8 to display around 1 second
-pub type EcgDownsampler = chain! {
+#[cfg(not(feature = "downsampler-light"))]
+pub type DownsamplerChain = chain! {
     DownSampler,
     DownSampler,
     DownSampler
 };
 
+#[cfg(not(feature = "downsampler-light"))]
+type EcgDownsampler = DownsamplerChain;
+
+#[cfg(not(feature = "downsampler-light"))]
+fn create_downsampler() -> DownsamplerChain {
+    Chain::new(DownSampler::new())
+        .append(DownSampler::new())
+        .append(DownSampler::new())
+}
+
+#[cfg(feature = "downsampler-light")]
+type EcgDownsampler = DownsamplerLight;
+
+#[cfg(feature = "downsampler-light")]
+fn create_downsampler() -> DownsamplerLight {
+    DownsamplerLight {
+        #[rustfmt::skip]
+        filter: macros::designfilt!(
+            "lowpassiir",
+            "FilterOrder", 2,
+            "HalfPowerFrequency", 35,
+            "SampleRate", 1000
+        ),
+        counter: 7,
+    }
+}
+
 pub const ECG_BUFFER_SIZE: usize = 90_000;
 
 // Two filter chains:
@@ -72,9 +127,7 @@ impl EcgObjects {
     fn new(hpf: Iir<'static, HighPass, 2>) -> Self {
         Self {
             filter: Chain::new(PowerLineFilter::new_1ksps([50.0])).append(hpf),
-            downsampler: Chain::new(DownSampler::new())
-                .append(DownSampler::new())
-                .append(DownSampler::new()),
+            downsampler: create_downsampler(),
             heart_rate_calculator: HeartRateCalculator::new(1000.0),
 
             #[rustfmt::skip]