Add syncword fuzzy detection

Frame decoder now tolerates bit error in syncword, removed syncword type
detection in demodulator code.

TG-81

openrtx/include/protocols/M17/M17Demodulator.h

@@ -145,7 +145,6 @@ private:
     uint16_t     frame_index;      ///< Index for filling the raw frame.
     frame_t      *activeFrame;     ///< Half frame, in demodulation.
     frame_t      *idleFrame;       ///< Half frame, free to be processed.
-    bool         isLSF;            ///< Indicates that we demodualated an LSF.
     bool         syncDetected;     ///< A syncword was detected.
     bool         locked;           ///< A syncword was correctly demodulated.
     bool         newFrame;         ///< A new frame has been fully decoded.

openrtx/src/protocols/M17/M17Demodulator.cpp

@@ -271,11 +271,6 @@ const frame_t& M17Demodulator::getFrame()
     return *activeFrame;
 }
 
-bool M17Demodulator::isFrameLSF()
-{
-    return isLSF;
-}
-
 bool M17::M17Demodulator::isLocked()
 {
     return locked;
@@ -324,7 +319,6 @@ bool M17Demodulator::update()
                 if (syncword.index != -1) // Valid syncword found
                 {
                     syncDetected = true;
-                    isLSF  = syncword.lsf;
                     offset = syncword.index + 1;
                     phase = 0;
                     frame_index = 0;
@@ -402,7 +396,7 @@ bool M17Demodulator::update()
                                                          lsf_syncword_bytes[1]);
 
                     // Too many errors in the syncword, lock is lost
-                    if ((hammingSync > 1) && (hammingLsf > 1))
+                    if ((hammingSync > 4) && (hammingLsf > 4))
                     {
                         syncDetected = false;
                         locked = false;

openrtx/src/protocols/M17/M17FrameDecoder.cpp

@@ -65,7 +65,9 @@ M17FrameType M17FrameDecoder::decodeFrame(const frame_t& frame)
     }
 
     // Stream data frame
-    if(syncWord == STREAM_SYNC_WORD)
+    uint8_t hd = __builtin_popcount(syncWord[0] ^ STREAM_SYNC_WORD[0])
+               + __builtin_popcount(syncWord[1] ^ STREAM_SYNC_WORD[1]);
+    if(hd <= 4)
     {
         decodeStream(data);
         return M17FrameType::STREAM;