fix(dmr): use flat discriminator and reject noise sync

DMRDecoder.pas

@@ -140,12 +140,15 @@ type
     FSyncCount: QWord;
     FLastSyncTick: QWord;
     FLastSyncSample: QWord;
+    FPendingSyncSample: array[TDMRSyncKind] of QWord;
+    FPendingSyncCount: array[TDMRSyncKind] of Byte;
     FMobileActiveBurst: Boolean;
 
     function PopSamples(var Buf: array of Single): Integer;
     procedure ProcessSample(S: Single);
     procedure ProcessSymbol(Phase: Integer; Symbol: Double);
     procedure NoteSync(Phase: Integer; Kind: TDMRSyncKind; Inverted: Boolean);
+    procedure LoseSync;
     function Digitize(Phase: Integer; Symbol: Double): Byte;
     procedure StartBurstTracking(Phase: Integer);
     procedure CompleteBurst;
@@ -174,6 +177,7 @@ const
   DMR_SYNC_HOLD_MS = 500;
   DMR_SYNC_MAX_ERRORS = 2;
   DMR_SUPERFRAME_SAMPLES = DMR_INPUT_RATE * 360 div 1000;
+  DMR_SYNC_CADENCE_TOLERANCE = DMR_SAMPLES_PER_SYM * 3;
 
   // One bit per DSD-FME sync character: '1'=0, '3'=1. These are the eight
   // ETSI DMR 48-bit sync patterns after collapsing each dibit to its sign.
@@ -337,6 +341,8 @@ begin
       FSyncCount := 0;
       FLastSyncTick := 0;
       FLastSyncSample := 0;
+      FillChar(FPendingSyncSample, SizeOf(FPendingSyncSample), 0);
+      FillChar(FPendingSyncCount, SizeOf(FPendingSyncCount), 0);
       FMobileActiveBurst := True;
     finally
       FStatusLock.Leave;
@@ -432,11 +438,19 @@ var
   Pat: LongWord;
   Dibit: Byte;
   V: Double;
-  DeltaSamples, CycleOffset: QWord;
+  DeltaSamples, CycleOffset, PendingSample: QWord;
   CandidateAllowed: Boolean;
 begin
   V := Symbol;
   if FInputInverted then V := -V;
+
+  // Stop assembling/decoding an endless stream of noise after the carrier
+  // vanishes.  Two superframes allow one damaged sync word without losing a
+  // valid call, while still closing the decoder in about 720 ms.
+  if (FLastSyncSample <> 0) and
+     (FSampleNo - FLastSyncSample > 2 * DMR_SUPERFRAME_SAMPLES +
+      DMR_SYNC_CADENCE_TOLERANCE) then
+    LoseSync;
   Dibit := Digitize(Phase, V);
 
   // Keep the 90 dibits ending at sync. Once the timing phase is selected this
@@ -479,7 +493,6 @@ begin
       // match lost almost every superframe in recorded handheld-radio IQ.
       DeltaSamples := FSampleNo - FLastSyncSample;
       CandidateAllowed := (FLastSyncSample = 0) or
-        (DeltaSamples > DMR_INPUT_RATE * 2) or
         (SYNC_KIND[i] = FSyncKind);
       // MS voice/data sync repeats every 360 ms. Cadence gating rejects
       // chance <=2-bit matches inside AMBE payload while still accepting a
@@ -494,6 +507,48 @@ begin
       end;
       if (Distance <= DMR_SYNC_MAX_ERRORS) and CandidateAllowed then
       begin
+        // Fuzzy 24-symbol matches occur often enough in open-channel noise to
+        // make mbelib emit occasional garbage.  Real voice sync repeats every
+        // 360 ms, so require three words of the same kind on that cadence
+        // before opening burst and vocoder processing.
+        if FLastSyncSample = 0 then
+        begin
+          PendingSample := FPendingSyncSample[SYNC_KIND[i]];
+          if PendingSample <> 0 then
+          begin
+            DeltaSamples := FSampleNo - PendingSample;
+            CycleOffset := DeltaSamples mod DMR_SUPERFRAME_SAMPLES;
+            if (DeltaSamples >= DMR_SUPERFRAME_SAMPLES -
+                 DMR_SYNC_CADENCE_TOLERANCE) and
+               ((CycleOffset <= DMR_SYNC_CADENCE_TOLERANCE) or
+                (CycleOffset >= DMR_SUPERFRAME_SAMPLES -
+                 DMR_SYNC_CADENCE_TOLERANCE)) then
+            begin
+              Inc(FPendingSyncCount[SYNC_KIND[i]]);
+              FPendingSyncSample[SYNC_KIND[i]] := FSampleNo;
+              // Three consecutive superframe syncs make accidental capture
+              // in random discriminator noise vanishingly unlikely.
+              if FPendingSyncCount[SYNC_KIND[i]] >= 3 then
+                NoteSync(Phase, SYNC_KIND[i], FInputInverted);
+            end
+            else if DeltaSamples > DMR_SUPERFRAME_SAMPLES +
+                    DMR_SYNC_CADENCE_TOLERANCE then
+            begin
+              FPendingSyncSample[SYNC_KIND[i]] := FSampleNo;
+              FPendingSyncCount[SYNC_KIND[i]] := 1;
+            end;
+          end;
+          if FLastSyncSample = 0 then
+          begin
+            if PendingSample = 0 then
+            begin
+              FPendingSyncSample[SYNC_KIND[i]] := FSampleNo;
+              FPendingSyncCount[SYNC_KIND[i]] := 1;
+            end;
+            Exit;
+          end;
+        end
+        else
           NoteSync(Phase, SYNC_KIND[i], FInputInverted);
         Exit;
       end;
@@ -501,6 +556,25 @@ begin
   end;
 end;
 
+procedure TDMRDecoder.LoseSync;
+begin
+  FStatusLock.Enter;
+  try
+    FSyncKind := dskNone;
+    FInverted := False;
+    FLastSyncTick := 0;
+    FLastSyncSample := 0;
+    FillChar(FPendingSyncSample, SizeOf(FPendingSyncSample), 0);
+    FillChar(FPendingSyncCount, SizeOf(FPendingSyncCount), 0);
+  finally
+    FStatusLock.Leave;
+  end;
+  FTrackPhase := -1;
+  FCurrentBurstPos := 0;
+  FMobileActiveBurst := True;
+  DMRMbeReset(FMbe);
+end;
+
 function TDMRDecoder.Digitize(Phase: Integer; Symbol: Double): Byte;
 var
   A, Threshold: Double;

WDSPEngine.pas

@@ -60,7 +60,7 @@ const
   MODE_DIGU = 8;
   MODE_DIGL = 9;
   MODE_WFM  = 10;
-  MODE_DMR  = 11;  // DMR receive: WDSP NFM discriminator -> DMRDecoder
+  MODE_DMR  = 11;  // DMR receive: flat WDSP discriminator -> DMRDecoder
 
   // Минимальная длина FIR у WDSP: create_* поднимают fircore с
   // nc = max(2048, dsp_size). В firmin.c nfor = nc / size, idxmask = nfor - 1,
@@ -73,6 +73,7 @@ const
   WFM_AF_LOW      = 20.0;
   WFM_AF_HIGH     = 15000.0;
   WFM_TAU_DE_US   = 50.0e-6;   // Европа/Россия (Америка — 75 мкс)
+  DMR_DEVIATION   = 2500.0;
   // Потолок dsp_rate для WFM. Вещательному каналу (200 кГц) хватает 192 кГц,
   // а гнать цепь на полном IQ-rate нельзя: при 576 кГц dsp_size стал бы 12288,
   // и fircore спланировал бы FFT на 2*12288 = 24576 точек. Это не степень
@@ -933,7 +934,10 @@ begin
     MODE_DIGU: Result := WDSP_DIGU;
     MODE_DIGL: Result := WDSP_DIGL;
     MODE_WFM:  Result := WDSP_RX_WFM;
-    MODE_DMR:  Result := WDSP_FM;
+    // The narrow-FM path always applies its 300..3000 Hz speech filters and
+    // de-emphasis.  Those filters collapse the four DMR discriminator levels.
+    // WFMD is a plain quadrature discriminator and permits flat data audio.
+    MODE_DMR:  Result := WDSP_RX_WFM;
     else       Result := WDSP_USB;
   end;
 end;
@@ -942,6 +946,7 @@ function TWDSPEngine.ModeToWDSPTX(Mode: Integer): Integer;
 // txaMode расходится с rxaMode после DRM — отдельный маппинг только для WFM.
 begin
   if Mode = MODE_WFM then Result := WDSP_TX_WFM
+  else if Mode = MODE_DMR then Result := WDSP_FM
   else Result := ModeToWDSP(Mode);
 end;
 
@@ -2693,7 +2698,13 @@ begin
   ApplyDSPRate(Mode);
   SetRXAMode(RXA_CHAN, ModeToWDSP(Mode));
   SetTXAMode(TXA_CHAN, ModeToWDSPTX(Mode));
-  if Mode = MODE_WFM then ApplyWFMSettings;
+  if Mode = MODE_WFM then ApplyWFMSettings
+  else if Mode = MODE_DMR then
+  begin
+    SetRXAWFMDeviation (RXA_CHAN, DMR_DEVIATION);
+    SetRXAWFMAFFilter  (RXA_CHAN, 20.0, 7000.0);
+    SetRXAWFMDeemphRun (RXA_CHAN, 0);
+  end;
   // НЕ вызываем ApplyDefaultFilter — фильтр устанавливается явно из UI
 end;
 
@@ -2929,6 +2940,9 @@ end;
 procedure TWDSPEngine.SetRXFMDeviation(Deviation: Double);
 begin
   if not FInitialized then Exit;
+  if FMode = MODE_DMR then
+    SetRXAWFMDeviation(RXA_CHAN, Deviation)
+  else
     SetRXAFMDeviation(RXA_CHAN, Deviation);
 end;
 

tests/dmr_frontend_test.pas

@@ -8,6 +8,7 @@ uses
 
 const
   BS_VOICE_SYNC = '131111333113313313113313';
+  DMR_TEST_SUPERFRAME_SAMPLES = DMR_INPUT_RATE * 360 div 1000;
 
 type
   TAudioSink = class
@@ -48,6 +49,23 @@ begin
   D.FeedAudio(L, R, Length(L));
 end;
 
+procedure FeedConfirmedSync(D: TDMRDecoder; const Pattern: string;
+  Invert: Boolean);
+var
+  L, R: array of Single;
+  GapSamples, RepeatIndex: Integer;
+begin
+  GapSamples := DMR_TEST_SUPERFRAME_SAMPLES -
+    (3 + Length(Pattern) * DMR_SAMPLES_PER_SYM + 20);
+  SetLength(L, GapSamples);
+  SetLength(R, GapSamples);
+  for RepeatIndex := 1 to 3 do
+  begin
+    FeedSync(D, Pattern, Invert);
+    if RepeatIndex < 3 then D.FeedAudio(L, R, GapSamples);
+  end;
+end;
+
 procedure TestBurst(D: TDMRDecoder);
 var
   Want, Got: array[0..DMR_BURST_DIBITS - 1] of Byte;
@@ -116,7 +134,7 @@ begin
   try
     D.OnAudio := Sink.AudioReady;
     D.SetEnabled(True);
-    FeedSync(D, BS_VOICE_SYNC, False);
+    FeedConfirmedSync(D, BS_VOICE_SYNC, False);
     Sleep(50);
     D.GetStatus(S);
     if (not S.Synced) or (S.SyncKind <> dskBSVoice) or S.Inverted then
@@ -128,7 +146,7 @@ begin
     D.SetEnabled(False);
     D.SetInverted(True);
     D.SetEnabled(True);
-    FeedSync(D, BS_VOICE_SYNC, True);
+    FeedConfirmedSync(D, BS_VOICE_SYNC, True);
     Sleep(50);
     D.GetStatus(S);
     if (not S.Synced) or (S.SyncKind <> dskBSVoice) or (not S.Inverted) then
@@ -140,6 +158,8 @@ begin
     D.SetEnabled(False);
     D.SetInverted(False);
     D.SetEnabled(True);
+    FeedConfirmedSync(D, BS_VOICE_SYNC, False);
+    Sleep(50);
     TestBurst(D);
     D.GetStatus(S);
     if S.VocoderAvailable and