Removed a printf left behind after debugging from M17 demodulator class and slightly cleaned up the code

openrtx/include/protocols/M17/M17Demodulator.h

@@ -42,7 +42,8 @@ typedef struct
 {
     int32_t index;
     bool lsf;
-} sync_t;
+}
+sync_t;
 
 class M17Demodulator
 {
@@ -153,20 +154,15 @@ private:
     /*
      * Convolution statistics computation
      */
-    float conv_ema = 0.0f;
+    float conv_ema   = 0.0f;    /// Exponential moving average from all the correlation values.
     float conv_emvar = 0.0f;
 
     /*
      * Quantization statistics computation
      */
-    float qnt_ema = 0.0f;
+    float qnt_ema = 0.0f;   ///< Exponential moving average from of the sliced samples.
-    float qnt_max = 0.0f;
+    float qnt_max = 0.0f;   ///< Max hold of the sliced samples
-    float qnt_min = 0.0f;
+    float qnt_min = 0.0f;   ///< Min hold of the sliced samples.
-
-    /**
-     * Deque containing the sliced samples
-     */
-    // std::deque<int16_t> samples_fifo;
 
     /**
      * Resets the exponential mean and variance/stddev computation.
@@ -181,13 +177,6 @@ private:
      */
     void updateCorrelationStats(int32_t value);
 
-    /**
-     * Returns the exponential moving average from all the correlation values.
-     *
-     * @returns float numerical value of the exponential moving average
-     */
-    float getCorrelationEma();
-
     /**
      * Returns the standard deviation from all the correlation values.
      *
@@ -208,27 +197,6 @@ private:
      */
     void updateQuantizationStats(int32_t offset);
 
-    /**
-     * Returns the exponential moving average from of the sliced samples.
-     *
-     * @returns float numerical value of the exponential moving average
-     */
-    float getQuantizationEma();
-
-    /**
-     * Returns the max hold of the sliced samples.
-     *
-     * @returns float numerical value of the max hold
-     */
-    float getQuantizationMax();
-
-    /**
-     * Returns the min hold of the sliced samples.
-     *
-     * @returns float numerical value of the min hold
-     */
-    float getQuantizationMin();
-
     /**
      * Computes the convolution between a stride of samples starting from
      * a given offset and a target waveform.

openrtx/src/protocols/M17/M17Demodulator.cpp

@@ -35,8 +35,7 @@
 #include <emulator.h>
 #endif
 
-namespace M17
+using namespace M17;
-{
 
 M17Demodulator::M17Demodulator()
 {
@@ -103,7 +102,7 @@ void M17Demodulator::stopBasebandSampling()
 
 void M17Demodulator::resetCorrelationStats()
 {
-    conv_ema = 0.0f;
+    conv_ema   = 0.0f;
     conv_emvar = 800000000.0f;
 }
 
@@ -119,11 +118,6 @@ void M17Demodulator::updateCorrelationStats(int32_t value)
     conv_emvar  = (1.0f - conv_stats_alpha) * (conv_emvar + delta * incr);
 }
 
-float M17Demodulator::getCorrelationEma()
-{
-    return conv_ema;
-}
-
 float M17Demodulator::getCorrelationStddev()
 {
     return sqrt(conv_emvar);
@@ -159,21 +153,6 @@ void M17Demodulator::updateQuantizationStats(int32_t offset)
         qnt_min *= qnt_stats_alpha;
 }
 
-float M17Demodulator::getQuantizationEma()
-{
-    return qnt_ema;
-}
-
-float M17Demodulator::getQuantizationMax()
-{
-    return qnt_max;
-}
-
-float M17Demodulator::getQuantizationMin()
-{
-    return qnt_min;
-}
-
 int32_t M17Demodulator::convolution(int32_t offset,
                                     int8_t *target,
                                     size_t target_size)
@@ -199,15 +178,14 @@ sync_t M17Demodulator::nextFrameSync(int32_t offset)
     #ifdef PLATFORM_LINUX
     FILE *csv_log = fopen("demod_log_1.csv", "a");
     #endif
+
     sync_t syncword = { -1, false };
     // Find peaks in the correlation between the baseband and the frame syncword
     // Leverage the fact LSF syncword is the opposite of the frame syncword
     // to detect both syncwords at once. Stop early because convolution needs
     // access samples ahead of the starting offset.
-    for(int32_t i = offset;
+    int32_t maxLen = static_cast < int32_t >(baseband.len - M17_BRIDGE_SIZE);
-        syncword.index == -1 &&
+    for(int32_t i = offset; (syncword.index == -1) && (i < maxLen); i++)
-        i < (int32_t) baseband.len - (int32_t) M17_BRIDGE_SIZE;
-        i++)
     {
         // If we are not locked search for a syncword
         int32_t conv = convolution(i, stream_syncword, M17_SYNCWORD_SYMBOLS);
@@ -218,28 +196,31 @@ sync_t M17Demodulator::nextFrameSync(int32_t offset)
             sample = basebandBridge[M17_BRIDGE_SIZE + i];
         else            // Otherwise use regular data buffer
             sample = baseband.data[i];
+
         #ifdef PLATFORM_LINUX
         fprintf(csv_log, "%" PRId16 ",%d,%f,%d\n",
                 sample,
-                conv - (int32_t) getCorrelationEma(),
+                conv - static_cast< int32_t >(conv_ema),
                 conv_threshold_factor * getCorrelationStddev(),
                 i);
         #endif
+
         // Positive correlation peak -> frame syncword
-        if (conv - (int32_t) getCorrelationEma() >
+        if ((conv - static_cast< int32_t >(conv_ema)) >
-            getCorrelationStddev() * conv_threshold_factor)
+            (getCorrelationStddev() * conv_threshold_factor))
         {
             syncword.lsf = false;
             syncword.index = i;
         }
         // Negative correlation peak -> LSF syncword
-        else if (conv - (int32_t) getCorrelationEma() <
+        else if ((conv - static_cast< int32_t >(conv_ema)) <
                  -(getCorrelationStddev() * conv_threshold_factor))
         {
             syncword.lsf = true;
             syncword.index = i;
         }
     }
+
     #ifdef PLATFORM_LINUX
     fclose(csv_log);
     #endif
@@ -254,10 +235,10 @@ int8_t M17Demodulator::quantize(int32_t offset)
     else            // Otherwise use regular data buffer
         sample = baseband.data[offset];
     // DC offset removal
-    int16_t s = sample - (int16_t) getQuantizationEma();
+    int16_t s = sample - static_cast< int16_t >(qnt_ema);
-    if (s > getQuantizationMax() / 2)
+    if (s > static_cast< int16_t >(qnt_max) / 2)
         return +3;
-    else if (s < getQuantizationMin() / 2)
+    else if (s < static_cast< int16_t >(qnt_min) / 2)
         return -3;
     else if (s > 0)
         return +1;
@@ -287,8 +268,10 @@ bool M17Demodulator::update()
     M17::sync_t syncword = { 0, false };
     int32_t offset = locked ? 0 : -(int32_t) M17_BRIDGE_SIZE;
     uint16_t decoded_syms = 0;
+
     // Read samples from the ADC
     baseband = inputStream_getData(basebandId);
+
     #ifdef PLATFORM_LINUX
     FILE *csv_log = fopen("demod_log_2.csv", "a");
     #endif
@@ -301,16 +284,12 @@ bool M17Demodulator::update()
         {
             float elem = static_cast< float >(baseband.data[i]);
             baseband.data[i] = static_cast< int16_t >(M17::rrc(elem));
-            //samples_fifo.push_back(baseband.data[i]);
-            //if (samples_fifo.size() > SCREEN_WIDTH)
-            //    samples_fifo.pop_front();
         }
 
         // Process the buffer
-        while(syncword.index != -1 &&
+        int32_t symbol_index = 0;
-              (offset + phase +
+        while((syncword.index != -1) &&
-              (int32_t) M17_SAMPLES_PER_SYMBOL * decoded_syms <
+              (symbol_index < static_cast< int32_t > (baseband.len)))
-              (int32_t) baseband.len))
         {
             // If we are not locked search for a syncword
             if (!locked)
@@ -319,7 +298,7 @@ bool M17Demodulator::update()
                 if (syncword.index != -1) // Lock was just acquired
                 {
                     locked = true;
-                    isLSF = syncword.lsf;
+                    isLSF  = syncword.lsf;
                     offset = syncword.index + 1;
                     frameIndex = 0;
                 }
@@ -328,9 +307,13 @@ bool M17Demodulator::update()
             else
             {
                 // Slice the input buffer to extract a frame and quantize
-                int32_t symbol_index = offset + phase + M17_SAMPLES_PER_SYMBOL * decoded_syms;
+                symbol_index = offset
+                             + phase
+                             + (M17_SAMPLES_PER_SYMBOL * decoded_syms);
+
                 updateQuantizationStats(symbol_index);
                 int8_t symbol = quantize(symbol_index);
+
                 #ifdef PLATFORM_LINUX
                 fprintf(csv_log, "%" PRId16 ",%f,%f,%d,%d\n",
                         baseband.data[symbol_index] - (int16_t) qnt_ema,
@@ -339,6 +322,7 @@ bool M17Demodulator::update()
                         symbol * 666,
                         frameIndex == 0 ? 2300 : symbol_index);
                 #endif
+
                 setSymbol<M17_FRAME_BYTES>(*activeFrame, frameIndex, symbol);
                 decoded_syms++;
                 frameIndex++;
@@ -349,27 +333,27 @@ bool M17Demodulator::update()
                     std::swap(activeFrame, idleFrame);
                     frameIndex = 0;
                     newFrame   = true;
-
-                    // DEBUG: print idleFrame bytes
-                    for(size_t i = 0; i < idleFrame->size(); i+=2)
-                    {
-                        if (i % 16 == 14)
-                            printf("\r\n");
-                        printf(" %02X%02X", (*idleFrame)[i], (*idleFrame)[i+1]);
-                    }
                 }
 
                 // If syncword is not valid, lock is lost, accept 2 bit errors
+                uint8_t hammingSync = hammingDistance((*activeFrame)[0],
+                                                      stream_syncword_bytes[0])
+                                    + hammingDistance((*activeFrame)[1],
+                                                      stream_syncword_bytes[1]);
+
+                uint8_t hammingLsf = hammingDistance((*activeFrame)[0],
+                                                     lsf_syncword_bytes[0])
+                                   + hammingDistance((*activeFrame)[1],
+                                                     lsf_syncword_bytes[1]);
+
                 if ((frameIndex == M17_SYNCWORD_SYMBOLS) &&
-                    (hammingDistance((*activeFrame)[0], stream_syncword_bytes[0]) +
+                    (hammingSync > 2) && (hammingLsf > 2))
-                     hammingDistance((*activeFrame)[1], stream_syncword_bytes[1]) > 2) &&
-                    (hammingDistance((*activeFrame)[0], lsf_syncword_bytes[0]) +
-                     hammingDistance((*activeFrame)[1], lsf_syncword_bytes[1]) > 2))
                 {
                     locked = false;
                     std::swap(activeFrame, idleFrame);
                     frameIndex = 0;
                     newFrame   = true;
+
                     #ifdef PLATFORM_MOD17
                     gpio_clearPin(SYNC_LED);
                     #endif // PLATFORM_MOD17
@@ -398,12 +382,10 @@ bool M17Demodulator::update()
                    sizeof(int16_t) * M17_BRIDGE_SIZE);
         }
     }
-    //gfx_plotData({0, 0}, SCREEN_WIDTH, SCREEN_HEIGHT, samples_fifo);
+
     #ifdef PLATFORM_LINUX
     fclose(csv_log);
     #endif
 
     return newFrame;
 }
-
-} /* M17 */