ATV Demod: added an averaging class for horizontal sync averaging

plugins/channelrx/demodatv/atvdemod.cpp

@@ -446,7 +446,7 @@ void ATVDemod::demod(Complex& c)
 
     if (blnComputeImage)
     {
-        m_objRegisteredATVScreen->setDataColor(m_intColIndex - m_intNumberSamplePerTop, intVal, intVal, intVal);
+        m_objRegisteredATVScreen->setDataColor(m_intColIndex - m_intNumberSamplePerTop, intVal, intVal, intVal); // TODO: the subtraction should be made with back porch number of samples
     }
 
     m_intColIndex++;
@@ -454,6 +454,7 @@ void ATVDemod::demod(Complex& c)
     //////////////////////
 
     m_blnSynchroDetected=false;
+
     if((m_objRunning.m_blnHSync) && (m_intRowIndex>1))
     {
         //********** Line Synchro  0-0-0 -> 0.3-0.3 0.3 **********
@@ -518,6 +519,8 @@ void ATVDemod::demod(Complex& c)
         }
     }
 
+    // TODO: stabilize horizontal sync by (exponential) averaging the column index at sync detection.
+    //       Then on the next block trigger on this column index average.
 
     //Horizontal Synchro
     if((m_intColIndex>=m_intNumberSamplePerLine)

plugins/channelrx/demodatv/atvdemod.h

@@ -297,6 +297,36 @@ private:
             }
     };
 
+    /**
+     * Exponential average using integers and alpha as the inverse of a power of two
+     */
+    class AvgExpInt
+    {
+    public:
+        AvgExpInt(int log2Alpha) : m_log2Alpha(log2Alpha), m_m1(0), m_start(true) {}
+        void reset() { m_start = true; }
+
+        int run(int m0)
+        {
+            if (m_start)
+            {
+                m_m1 = m0;
+                m_start = false;
+                return m0;
+            }
+            else
+            {
+                m_m1 = m0 + m_m1 - (m_m1>>m_log2Alpha);
+                return m_m1>>m_log2Alpha;
+            }
+        }
+
+    private:
+        int m_log2Alpha;
+        int m_m1;
+        bool m_start;
+    };
+
     //*************** SCOPE  ***************
 
     BasebandSampleSink* m_objScopeSink;