First implementation of the HR sensor using 100% foss code (ported from waspos)

src/components/heartrate/Biquad.cpp

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+#include "Biquad.h"
+
+using namespace Pinetime::Controllers;
+
+Biquad::Biquad(float b0, float b1, float b2, float a1, float a2) : b0{b0}, b1{b1}, b2{b2}, a1{a1}, a2{a2} {
+
+}
+
+float Biquad::Step(float x) {
+  auto v1 = this->v1;
+  auto v2 = this->v2;
+
+  auto v = x - (a1 * v1) - (a2 * v2);
+  auto y = (b0 * v) + (b1 * v1) + (b2 * v2);
+
+  this->v2 = v1;
+  this->v1 = v;
+
+  return y;
+}

src/components/heartrate/Biquad.h

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+#pragma once
+
+namespace Pinetime {
+  namespace Controllers {
+    /// Direct Form II Biquad Filter
+    class Biquad {
+    public:
+      Biquad(float b0, float  b1, float b2, float a1, float a2);
+      float Step(float x);
+
+    private:
+      float b0;
+      float b1;
+      float b2;
+      float a1;
+      float a2;
+
+      float v1 = 0.0f;
+      float v2 = 0.0f;
+    };
+  }
+}

src/components/heartrate/HeartRateController.cpp

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+#include "HeartRateController.h"
+#include <heartratetask/HeartRateTask.h>
+
+using namespace Pinetime::Controllers;
+
+void HeartRateController::Update(HeartRateController::States newState, uint8_t heartRate) {
+  this->state = newState;
+  this->heartRate = heartRate;
+}
+
+void HeartRateController::Start() {
+  if(task != nullptr)
+    task->PushMessage(Pinetime::Applications::HeartRateTask::Messages::StartMeasurement);
+}
+
+void HeartRateController::Stop() {
+  if(task != nullptr)
+    task->PushMessage(Pinetime::Applications::HeartRateTask::Messages::StopMeasurement);
+}
+
+void HeartRateController::SetHeartRateTask(Pinetime::Applications::HeartRateTask *task) {
+  this->task = task;
+}

src/components/heartrate/HeartRateController.h

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+#pragma once
+
+#include <cstdint>
+
+namespace Pinetime {
+  namespace Applications {
+    class HeartRateTask;
+  }
+  namespace Controllers {
+    class HeartRateController {
+    public:
+      enum class States { NotEnoughData, NoTouch, Running};
+
+      void Start();
+      void Stop();
+      void Update(States newState, uint8_t heartRate);
+
+      void SetHeartRateTask(Applications::HeartRateTask* task);
+      States State() const { return state; }
+      uint8_t HeartRate() const { return heartRate; }
+
+    private:
+      Applications::HeartRateTask* task = nullptr;
+      States state = States::NotEnoughData;
+      uint8_t heartRate = 0;
+    };
+  }
+}

src/components/heartrate/Ppg.cpp

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+#include <vector>
+#include <nrf_log.h>
+#include "Ppg.h"
+using namespace Pinetime::Controllers;
+
+namespace {
+  // TODO no vector!
+  int Compare(int* d1, int* d2, size_t count) {
+    int e = 0;
+    for(int i = 0; i < count; i++) {
+      auto d = d1[i] - d2[i];
+      e += d * d;
+    }
+    return e;
+  }
+
+  int CompareShift(int* d, int shift, size_t count) {
+    return Compare(d +shift, d, count - shift);
+  }
+
+  int Trough(int* d, size_t size, float mn, float mx) {
+    auto z2 = CompareShift(d, mn-2, size);
+    auto z1 = CompareShift(d, mn-1, size);
+    for(int i = mn; i < mx + 1; i++) {
+      auto z = CompareShift(d, i, size);
+      if(z2 > z1 && z1 < z)
+        return i;
+      z2 = z1;
+      z1 = z;
+    }
+    return -1;
+  }
+}
+
+Ppg::Ppg(float spl) : offset{spl},
+                      hpf{0.87033078, -1.74066156, 0.87033078,-1.72377617, 0.75754694},
+                      agc{20, 0.971, 2},
+                      lpf{0.11595249, 0.23190498, 0.11595249,-0.72168143, 0.18549138} {
+
+}
+
+int Ppg::Preprocess(float spl) {
+  spl -= offset;
+  spl = hpf.Step(spl);
+  spl = agc.Step(spl);
+  spl = lpf.Step(spl);
+
+  auto spl_int = static_cast<int>(spl);
+
+  if(dataIndex < 200)
+    data[dataIndex++] = spl_int;
+  return spl_int;
+}
+
+float Ppg::HeartRate() {
+  if(dataIndex < 200)
+    return 0;
+
+  NRF_LOG_INFO("PREPROCESS, offset = %d", offset);
+  auto hr = ProcessHeartRate();
+  dataIndex = 0;
+  return hr;
+}
+
+int cccount = 0;
+float Ppg::ProcessHeartRate() {
+
+  if(cccount > 2)
+    asm("nop");
+  cccount ++;
+  auto t0 = Trough(data.data(), dataIndex, 7, 48);
+  if(t0 < 0)
+    return 0;
+
+  float t1 = t0 * 2;
+  t1 = Trough(data.data(), dataIndex, t1-5, t1+5);
+  if(t1 < 0)
+    return 0;
+
+  float t2 = static_cast<int>(t1 * 3) / 2;
+  t2 = Trough(data.data(), dataIndex, t2 - 5, t2 + 5);
+  if(t2 < 0)
+    return 0;
+
+  float t3 = static_cast<int>(t2 * 4) / 3;
+  t3 = Trough(data.data(), dataIndex, t3 - 4, t3 + 4);
+  if(t3 < 0)
+    return static_cast<int>(60 * 24 * 3) / static_cast<int>(t2);
+
+  return static_cast<int>(60 * 24 * 4) / static_cast<int>(t3);
+}
+
+void Ppg::SetOffset(uint16_t offset) {
+  this->offset = offset;
+  dataIndex = 0;
+}

src/components/heartrate/Ppg.h

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+#pragma once
+
+#include <array>
+#include "Biquad.h"
+#include "Ptagc.h"
+
+namespace Pinetime {
+  namespace Controllers {
+    class Ppg {
+    public:
+      explicit Ppg(float spl);
+
+      int Preprocess(float spl);
+      float HeartRate();
+
+      void SetOffset(uint16_t i);
+
+    private:
+      std::array<int, 200> data;
+      size_t dataIndex = 0;
+      float offset;
+      Biquad hpf;
+      Ptagc agc;
+      Biquad lpf;
+
+
+      float ProcessHeartRate();
+    };
+  }
+}

src/components/heartrate/Ptagc.cpp

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+#include <cmath>
+#include "Ptagc.h"
+
+using namespace Pinetime::Controllers;
+
+Ptagc::Ptagc(float start, float decay, float threshold) : peak{start}, decay{decay}, boost{1.0f/decay}, threshold{threshold} {
+
+}
+
+float Ptagc::Step(float spl) {
+  if(std::abs(spl) > peak)
+    peak *= boost;
+  else
+    peak *= decay;
+
+  if((spl > (peak * threshold)) || (spl < (peak * -threshold)))
+    return 0.0f;
+
+  spl = 100.0f * spl / (2.0f * peak);
+  return spl;
+}

src/components/heartrate/Ptagc.h

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+#pragma once
+
+namespace Pinetime {
+  namespace Controllers {
+    class Ptagc {
+    public:
+      Ptagc(float start, float decay, float threshold);
+      float Step(float spl);
+
+    private:
+      float peak;
+      float decay;
+      float boost;
+      float threshold;
+
+    };
+  }
+}