fix(dmr): avoid stale and mislabeled talkgroups

DMRDecoder.pas

@@ -166,6 +166,7 @@ type
     function GetLastBurst(var Dibits: array of Byte; out Sequence: QWord): Boolean;
 
     class function SyncKindName(Kind: TDMRSyncKind): string; static;
+    class function LinkControlTargetText(const S: TDMRStatus): string; static;
     property Enabled: Boolean read FEnabled;
     property OnAudio: TDMRAudioEvent read FOnAudio write FOnAudio;
   end;
@@ -580,6 +581,17 @@ begin
   FFixedNegativeOuter := 0;
   FFixedCenter := 0;
   FMobileActiveBurst := True;
+  // LC belongs to a call/slot, not to the tuned frequency forever. Keeping it
+  // across carrier loss made a newly acquired call briefly inherit the old
+  // target and display the same apparent TG on unrelated transmissions.
+  FillChar(FLinkControl, SizeOf(FLinkControl), 0);
+  FLastLCSlot := -1;
+  FSelectedSlot := -1;
+  FLastSelectedVoiceTick := 0;
+  FColorCodeValid := False;
+  FColorCode := 0;
+  FLastDataType := 0;
+  FSlotTypeCorrectedBits := 0;
   DMRMbeReset(FMbe);
 end;
 
@@ -947,4 +959,18 @@ begin
   end;
 end;
 
+class function TDMRDecoder.LinkControlTargetText(
+  const S: TDMRStatus): string;
+begin
+  Result := '';
+  if not S.LinkControlValid or (S.TargetID = 0) then Exit;
+  // ETSI Full Link Control opcode 0 is Group Voice Channel User; opcode 3 is
+  // Unit-to-Unit Voice Channel User. Other/vendor opcodes may reuse these 24
+  // bits for different data, so do not mislabel them as a talkgroup.
+  case S.LCOpcode of
+    0: Result := 'TG' + IntToStr(S.TargetID);
+    3: Result := 'ID' + IntToStr(S.TargetID);
+  end;
+end;
+
 end.