Auto gain control

Author: mark9064

src/components/heartrate/IIR.h

@@ -40,6 +40,13 @@ namespace Pinetime {
         }
       }
 
+      void Scale(float scaleFactor) {
+        for (std::size_t i = 0; i < NSections; i++) {
+          filterStates[i].s1 *= scaleFactor;
+          filterStates[i].s2 *= scaleFactor;
+        }
+      }
+
     private:
       std::array<FilterState, NSections> filterStates;
       const std::array<SOSCoeffs, NSections>& coeffs;

src/components/heartrate/Ppg.cpp

@@ -28,6 +28,10 @@ bool Ppg::SufficientData() const {
   return ready;
 }
 
+void Ppg::ScaleHrs(float scaleFactor) {
+  ppgFilter.Scale(scaleFactor);
+}
+
 void Ppg::Ingest(uint16_t hrs, int16_t accX, int16_t accY, int16_t accZ) {
   // Acceleration is normalised to 1024=1G in the BMA driver
   float accXNorm = static_cast<float>(accX) / 1024.f;

src/components/heartrate/Ppg.h

@@ -21,6 +21,7 @@ namespace Pinetime {
       std::optional<uint8_t> HeartRate();
       void Reset();
       [[nodiscard]] bool SufficientData() const;
+      void ScaleHrs(float scaleFactor);
       static constexpr float sampleDuration = 0.048f;
 
     private: