motioncontroller: Add functions for analysis

These are functions for converting acceleration due to gravity to angles
in degrees, and some statistical analysis including the mean and
variance.

src/components/motion/MotionController.cpp

@@ -2,8 +2,39 @@
 
 #include <task.h>
 
+#include "utility/Math.h"
+
 using namespace Pinetime::Controllers;
 
+namespace {
+  constexpr inline int32_t Clamp(int32_t val, int32_t min, int32_t max) {
+    return val < min ? min : (val > max ? max : val);
+  }
+
+  // only returns meaningful values if inputs are acceleration due to gravity
+  int16_t DegreesRolled(int16_t y, int16_t z, int16_t prevY, int16_t prevZ) {
+    int16_t prevYAngle = Pinetime::Utility::Asin(Clamp(prevY * 32, -32767, 32767));
+    int16_t yAngle = Pinetime::Utility::Asin(Clamp(y * 32, -32767, 32767));
+
+    if (z < 0 && prevZ < 0) {
+      return yAngle - prevYAngle;
+    }
+    if (prevZ < 0) {
+      if (y < 0) {
+        return -prevYAngle - yAngle - 180;
+      }
+      return -prevYAngle - yAngle + 180;
+    }
+    if (z < 0) {
+      if (y < 0) {
+        return prevYAngle + yAngle + 180;
+      }
+      return prevYAngle + yAngle - 180;
+    }
+    return prevYAngle - yAngle;
+  }
+}
+
 void MotionController::Update(int16_t x, int16_t y, int16_t z, uint32_t nbSteps) {
   if (this->nbSteps != nbSteps && service != nullptr) {
     service->OnNewStepCountValue(nbSteps);
@@ -23,6 +54,8 @@ void MotionController::Update(int16_t x, int16_t y, int16_t z, uint32_t nbSteps)
   zHistory++;
   zHistory[0] = z;
 
+  stats = GetAccelStats();
+
   int32_t deltaSteps = nbSteps - this->nbSteps;
   if (deltaSteps > 0) {
     currentTripSteps += deltaSteps;
@@ -30,6 +63,30 @@ void MotionController::Update(int16_t x, int16_t y, int16_t z, uint32_t nbSteps)
   this->nbSteps = nbSteps;
 }
 
+MotionController::AccelStats MotionController::GetAccelStats() const {
+  AccelStats stats;
+
+  for (uint8_t i = 0; i < AccelStats::numHistory; i++) {
+    stats.yMean += yHistory[histSize - i];
+    stats.zMean += zHistory[histSize - i];
+    stats.prevYMean += yHistory[1 + i];
+    stats.prevZMean += zHistory[1 + i];
+  }
+  stats.yMean /= AccelStats::numHistory;
+  stats.zMean /= AccelStats::numHistory;
+  stats.prevYMean /= AccelStats::numHistory;
+  stats.prevZMean /= AccelStats::numHistory;
+
+  for (uint8_t i = 0; i < AccelStats::numHistory; i++) {
+    stats.yVariance += (yHistory[histSize - i] - stats.yMean) * (yHistory[histSize - i] - stats.yMean);
+    stats.zVariance += (zHistory[histSize - i] - stats.zMean) * (zHistory[histSize - i] - stats.zMean);
+  }
+  stats.yVariance /= AccelStats::numHistory;
+  stats.zVariance /= AccelStats::numHistory;
+
+  return stats;
+}
+
 bool MotionController::ShouldRaiseWake(bool isSleeping) {
   if ((x + 335) <= 670 && zHistory[0] < 0) {
     if (!isSleeping) {

src/components/motion/MotionController.h

@@ -68,6 +68,22 @@ namespace Pinetime {
       TickType_t lastTime = 0;
       TickType_t time = 0;
 
+      struct AccelStats {
+        static constexpr uint8_t numHistory = 2;
+
+        int16_t yMean = 0;
+        int16_t zMean = 0;
+        int16_t prevYMean = 0;
+        int16_t prevZMean = 0;
+
+        uint32_t yVariance = 0;
+        uint32_t zVariance = 0;
+      };
+
+      AccelStats GetAccelStats() const;
+
+      AccelStats stats = {};
+
       int16_t lastX = 0;
       int16_t x = 0;
       int16_t lastYForRaiseWake = 0;