Improved detection of M17 frames to avoid spurious decodes

decoder_modules/m17_decoder/src/m17dsp.h

@@ -27,6 +27,10 @@ extern "C" {
 #define M17_RAW_FRAME_SIZE       384
 #define M17_CUT_FRAME_SIZE       368
 
+#define M17_MAX_FN          0x7FFF
+#define M17_END_FN          0x8000
+#define M17_STREAM_TIMEOUT  500
+
 const uint8_t M17_LSF_SYNC[16] = { 0, 1, 0, 1, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 1, 1 };
 const uint8_t M17_STF_SYNC[16] = { 1, 1, 1, 1, 1, 1, 1, 1, 0, 1, 0, 1, 1, 1, 0, 1 };
 const uint8_t M17_PKF_SYNC[16] = { 0, 1, 1, 1, 0, 1, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1 };
@@ -438,6 +442,7 @@ namespace dsp {
 
         void init(stream<uint8_t>* in) {
             _in = in;
+            lastConseqTime = std::chrono::high_resolution_clock::now();
 
             codec = codec2_create(CODEC2_MODE_3200);
             sampsPerC2Frame = codec2_samples_per_frame(codec);
@@ -460,10 +465,46 @@ namespace dsp {
             block::tempStart();
         }
 
+        bool isReceiving() {
+            std::lock_guard<std::recursive_mutex> lck(recvMtx);
+            return receiving && !timedOut();
+        }
+
+        bool timedOut() {
+            std::lock_guard<std::recursive_mutex> lck(recvMtx);
+            auto now = std::chrono::high_resolution_clock::now();
+            return std::chrono::duration_cast<std::chrono::milliseconds>(now - lastConseqTime).count() > M17_STREAM_TIMEOUT;
+        }
+
         int run() {
             int count = _in->read();
             if (count < 0) { return -1; }
 
+            // Decode frame number
+            uint16_t fn = ((uint16_t)_in->readBuf[0] << 8) | _in->readBuf[1];
+
+            // Check if we need to start or stop receiving
+            bool consecutive = ((((int)fn - (int)lastFn + M17_END_FN) % M17_END_FN) == 1);
+            if (!receiving && consecutive) {
+                std::lock_guard<std::recursive_mutex> lck(recvMtx);
+                receiving = true;
+            }
+            else if (receiving && consecutive) {
+                std::lock_guard<std::recursive_mutex> lck(recvMtx);
+                lastConseqTime = std::chrono::high_resolution_clock::now();;
+            }
+            else if (receiving && !consecutive && timedOut()) {
+                std::lock_guard<std::recursive_mutex> lck(recvMtx);
+                receiving = false;
+            }
+
+            // Save FN and if we have to stop receiving and it's not the last frame, stop
+            lastFn = fn;
+            if (!receiving) {
+                _in->flush();
+                return count;
+            }
+
             // Decode both parts using codec
             codec2_decode(codec, int16Audio, &_in->readBuf[2]);
             codec2_decode(codec, &int16Audio[sampsPerC2Frame], &_in->readBuf[2 + 8]);
@@ -485,6 +526,11 @@ namespace dsp {
     private:
         stream<uint8_t>* _in;
 
+        std::recursive_mutex recvMtx;
+        bool receiving = false;
+        uint16_t lastFn = 0;
+        std::chrono::high_resolution_clock::time_point lastConseqTime;
+
         int16_t* int16Audio;
         float* floatAudio;
 
@@ -637,6 +683,10 @@ namespace dsp {
             demod.setInput(input);
         }
 
+        bool isReceiving() {
+            return decodeAudio.isReceiving();
+        }
+
         stream<float>* diagOut = NULL;
         stream<stereo_t>* out = NULL;
 

decoder_modules/m17_decoder/src/main.cpp

@@ -227,6 +227,15 @@ private:
             config.release(true);
         }
 
+        ImGui::TextUnformatted("Status:");
+        ImGui::SameLine();
+        if (_this->decoder.isReceiving()) {
+            ImGui::TextColored(ImVec4(0.0, 1.0, 0.0, 1.0), "Receiving");
+        }
+        else {
+            ImGui::TextUnformatted("Idle");
+        }
+
         if (!_this->enabled) { style::endDisabled(); }
     }