ewsdr/DMRDecoder.pas

unit DMRDecoder;

{
  DMR 4FSK receive front-end.

  Input is 48 kHz discriminator audio from the WDSP FM demodulator. The DSP
  callback only copies complete blocks into a bounded ring; symbol timing and
  sync detection run in TDMRDecoderThread and can never stall the WDSP thread.

  This first layer deliberately stops at burst sync. The following layer will
  pass aligned dibits to the trimmed dsd-fme DMR/FEC/AMBE core.
}

{$IFDEF FPC}
  {$MODE Delphi}
{$ENDIF}

interface

uses
  Classes, SysUtils, SyncObjs, Math, DMRBindings, DMRProtocol;

const
  DMR_INPUT_RATE       = 48000;
  DMR_SYMBOL_RATE      = 4800;
  DMR_SAMPLES_PER_SYM  = DMR_INPUT_RATE div DMR_SYMBOL_RATE;
  DMR_RING_SIZE        = 65536; // >1.3 s at 48 kHz, power of two
  DMR_BURST_DIBITS     = 144;
  DMR_SYNC_END_DIBIT   = 89;    // sync occupies burst dibits 66..89
  DMR_VOICE_FRAME_SAMPLES = DMR_PCM_SAMPLES; // 20 ms at 8 kHz

type
  TDMRAudioEvent = procedure(const PCM: array of Single; Count: Integer) of object;

  TDMRSyncKind = (
    dskNone,
    dskBSData, dskBSVoice,
    dskMSData, dskMSVoice,
    dskDirectTS1Data, dskDirectTS1Voice,
    dskDirectTS2Data, dskDirectTS2Voice
  );

  TDMRStatus = record
    Enabled: Boolean;
    Synced: Boolean;
    SyncKind: TDMRSyncKind;
    Inverted: Boolean;
    SyncCount: QWord;
    BurstCount: QWord;
    BurstDibits: Integer;
    DroppedSamples: QWord;
    SignalRMS: Single;
    LastSyncAgeMs: QWord;
    VocoderAvailable: Boolean;
    CACHValid: Boolean;
    Slot: Integer;
    LCSS: Integer;
    SlotTypeValid: Boolean;
    ColorCode: Integer;
    DataType: Integer;
    SlotTypeCorrectedBits: Integer;
    LinkControlValid: Boolean;
    LCSlot: Integer;
    LCOpcode: Integer;
    ServiceOptions: Integer;
    TargetID: LongWord;
    SourceID: LongWord;
    SelectedSlot: Integer;
    VoiceFrameCount: QWord;
    VoiceErrorCount: QWord;
  end;

  TDMRDecoder = class;

  TDMRDecoderThread = class(TThread)
  private
    FOwner: TDMRDecoder;
  protected
    procedure Execute; override;
  public
    constructor Create(AOwner: TDMRDecoder);
  end;

  TDMRDecoder = class
  private
    FEnabled: Boolean;
    FRingLock: TCriticalSection;
    FDSPLock: TCriticalSection;
    FStatusLock: TCriticalSection;
    FWake: PRTLEvent;
    FThread: TDMRDecoderThread;
    FMbe: Pointer;
    FRing: array[0..DMR_RING_SIZE - 1] of Single;
    FReadPos, FWritePos: Integer;
    FDropped: QWord;

    FSampleWindow: array[0..DMR_SAMPLES_PER_SYM - 1] of Double;
    FWindowPos, FWindowCount: Integer;
    FWindowSum: Double;
    FSampleNo: QWord;
    FSyncShift: array[0..DMR_SAMPLES_PER_SYM - 1] of LongWord;
    FOuterLevel: array[0..DMR_SAMPLES_PER_SYM - 1] of Double;
    FDibitHistory: array[0..DMR_SAMPLES_PER_SYM - 1,
                         0..DMR_SYNC_END_DIBIT] of Byte;
    FHistoryPos: array[0..DMR_SAMPLES_PER_SYM - 1] of Integer;
    FHistoryCount: array[0..DMR_SAMPLES_PER_SYM - 1] of Integer;
    FMagHistory: array[0..DMR_SAMPLES_PER_SYM - 1, 0..23] of Double;
    FMagPos: array[0..DMR_SAMPLES_PER_SYM - 1] of Integer;
    FMagSum: array[0..DMR_SAMPLES_PER_SYM - 1] of Double;
    FBestSyncQuality: Double;
    FTrackPhase: Integer;
    FCurrentBurst: TDMRDibitBurst;
    FCurrentBurstPos: Integer;
    FLastBurst: TDMRDibitBurst;
    FLastBurstInfo: TDMRBurstInfo;
    FLinkControl: array[0..1] of TDMRLinkControl;
    FLastLCSlot: Integer;
    FColorCodeValid: Boolean;
    FColorCode, FLastDataType, FSlotTypeCorrectedBits: Integer;
    FSelectedSlot: Integer;
    FLastSelectedVoiceTick: QWord;
    FVoiceFrameCount, FVoiceErrorCount: QWord;
    FOnAudio: TDMRAudioEvent;
    FBurstCount: QWord;
    FRMSSq: Double;

    FSyncKind: TDMRSyncKind;
    FInputInverted: Boolean;
    FInverted: Boolean;
    FSyncCount: QWord;
    FLastSyncTick: QWord;

    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);
    function Digitize(Phase: Integer; Symbol: Double): Byte;
    procedure StartBurstTracking(Phase: Integer);
    procedure CompleteBurst;
    procedure DecodeVoiceBurst;
    procedure ResetDSP;
  public
    constructor Create;
    destructor Destroy; override;

    procedure SetEnabled(On_: Boolean);
    procedure SetInverted(On_: Boolean);
    procedure FeedAudio(const Left, Right: array of Single; Count: Integer);
    procedure GetStatus(out S: TDMRStatus);
    function GetLastBurst(var Dibits: array of Byte; out Sequence: QWord): Boolean;

    class function SyncKindName(Kind: TDMRSyncKind): string; static;
    property Enabled: Boolean read FEnabled;
    property OnAudio: TDMRAudioEvent read FOnAudio write FOnAudio;
  end;

implementation

const
  DMR_SYNC_MASK = LongWord($00FFFFFF);
  DMR_SYNC_HOLD_MS = 500;

  // 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.
  SYNC_TEXT: array[0..7] of string = (
    '313333111331131131331131', // BS data
    '131111333113313313113313', // BS voice
    '311131133313133331131113', // MS data
    '133313311131311113313331', // MS voice
    '331333313111313133311111', // direct TS1 data
    '113111131333131311133333', // direct TS1 voice
    '311311111333113333133311', // direct TS2 data
    '133133333111331111311133'  // direct TS2 voice
  );

  SYNC_KIND: array[0..7] of TDMRSyncKind = (
    dskBSData, dskBSVoice, dskMSData, dskMSVoice,
    dskDirectTS1Data, dskDirectTS1Voice,
    dskDirectTS2Data, dskDirectTS2Voice
  );

function SyncBits(const Text: string): LongWord;
var
  i: Integer;
begin
  Result := 0;
  for i := 1 to Length(Text) do
  begin
    Result := (Result shl 1) and DMR_SYNC_MASK;
    if Text[i] = '3' then Result := Result or 1;
  end;
end;

constructor TDMRDecoderThread.Create(AOwner: TDMRDecoder);
begin
  inherited Create(True);
  FreeOnTerminate := False;
  FOwner := AOwner;
end;

procedure TDMRDecoderThread.Execute;
var
  Buf: array[0..2047] of Single;
  N, i: Integer;
begin
  while not Terminated do
  begin
    // Pop and process share the DSP lock with ResetDSP. Otherwise a reset can
    // clear the ring after this thread popped an old block but before it was
    // processed, allowing stale symbols to leak into the new mode/session.
    FOwner.FDSPLock.Enter;
    try
      N := FOwner.PopSamples(Buf);
      for i := 0 to N - 1 do
        FOwner.ProcessSample(Buf[i]);
    finally
      FOwner.FDSPLock.Leave;
    end;
    if N = 0 then
    begin
      RTLEventWaitFor(FOwner.FWake, 100);
      Continue;
    end;
  end;
end;

constructor TDMRDecoder.Create;
begin
  inherited Create;
  FRingLock := TCriticalSection.Create;
  FDSPLock := TCriticalSection.Create;
  FStatusLock := TCriticalSection.Create;
  FWake := RTLEventCreate;
  FThread := TDMRDecoderThread.Create(Self);
  if DMRLoad then FMbe := DMRMbeCreate(3);
  ResetDSP;
  FThread.Start;
end;

destructor TDMRDecoder.Destroy;
begin
  if FThread <> nil then
  begin
    FThread.Terminate;
    RTLEventSetEvent(FWake);
    FThread.WaitFor;
    FreeAndNil(FThread);
  end;
  DMRMbeDestroy(FMbe);
  FMbe := nil;
  DMRUnload;
  RTLEventDestroy(FWake);
  FStatusLock.Free;
  FDSPLock.Free;
  FRingLock.Free;
  inherited Destroy;
end;

procedure TDMRDecoder.ResetDSP;
begin
  FDSPLock.Enter;
  try
    FRingLock.Enter;
    try
      FReadPos := 0;
      FWritePos := 0;
      FDropped := 0;
    finally
      FRingLock.Leave;
    end;
    FillChar(FSampleWindow, SizeOf(FSampleWindow), 0);
    FillChar(FSyncShift, SizeOf(FSyncShift), 0);
    FillChar(FOuterLevel, SizeOf(FOuterLevel), 0);
    FillChar(FDibitHistory, SizeOf(FDibitHistory), 0);
    FillChar(FHistoryPos, SizeOf(FHistoryPos), 0);
    FillChar(FHistoryCount, SizeOf(FHistoryCount), 0);
    FillChar(FMagHistory, SizeOf(FMagHistory), 0);
    FillChar(FMagPos, SizeOf(FMagPos), 0);
    FillChar(FMagSum, SizeOf(FMagSum), 0);
    FBestSyncQuality := 0;
    FillChar(FCurrentBurst, SizeOf(FCurrentBurst), 0);
    FillChar(FLastBurst, SizeOf(FLastBurst), 0);
    FillChar(FLastBurstInfo, SizeOf(FLastBurstInfo), 0);
    FillChar(FLinkControl, SizeOf(FLinkControl), 0);
    FLastLCSlot := -1;
    FColorCodeValid := False;
    FColorCode := 0;
    FLastDataType := 0;
    FSlotTypeCorrectedBits := 0;
    FSelectedSlot := -1;
    FLastSelectedVoiceTick := 0;
    FVoiceFrameCount := 0;
    FVoiceErrorCount := 0;
    DMRMbeReset(FMbe);
    FTrackPhase := -1;
    FCurrentBurstPos := 0;
    FBurstCount := 0;
    FWindowPos := 0;
    FWindowCount := 0;
    FWindowSum := 0;
    FSampleNo := 0;
    FRMSSq := 0;
    FStatusLock.Enter;
    try
      FSyncKind := dskNone;
      FInverted := False;
      FSyncCount := 0;
      FLastSyncTick := 0;
    finally
      FStatusLock.Leave;
    end;
  finally
    FDSPLock.Leave;
  end;
end;

procedure TDMRDecoder.SetEnabled(On_: Boolean);
begin
  if FEnabled = On_ then Exit;
  FEnabled := On_;
  ResetDSP;
  if On_ then RTLEventSetEvent(FWake);
end;

procedure TDMRDecoder.SetInverted(On_: Boolean);
begin
  if FInputInverted = On_ then Exit;
  FInputInverted := On_;
  if FEnabled then ResetDSP;
end;

procedure TDMRDecoder.FeedAudio(const Left, Right: array of Single;
  Count: Integer);
var
  i, Next: Integer;
  V: Single;
begin
  if not FEnabled or (Count <= 0) then Exit;
  Count := Min(Count, Min(Length(Left), Length(Right)));
  FRingLock.Enter;
  try
    for i := 0 to Count - 1 do
    begin
      Next := (FWritePos + 1) and (DMR_RING_SIZE - 1);
      if Next = FReadPos then
      begin
        Inc(FDropped);
        Continue;
      end;
      V := 0.5 * (Left[i] + Right[i]);
      FRing[FWritePos] := V;
      FWritePos := Next;
    end;
  finally
    FRingLock.Leave;
  end;
  RTLEventSetEvent(FWake);
end;

function TDMRDecoder.PopSamples(var Buf: array of Single): Integer;
begin
  Result := 0;
  FRingLock.Enter;
  try
    while (FReadPos <> FWritePos) and (Result < Length(Buf)) do
    begin
      Buf[Result] := FRing[FReadPos];
      FReadPos := (FReadPos + 1) and (DMR_RING_SIZE - 1);
      Inc(Result);
    end;
  finally
    FRingLock.Leave;
  end;
end;

procedure TDMRDecoder.ProcessSample(S: Single);
var
  Phase: Integer;
  Sym: Double;
begin
  FRMSSq := FRMSSq + 0.001 * (S * S - FRMSSq);
  FWindowSum := FWindowSum - FSampleWindow[FWindowPos] + S;
  FSampleWindow[FWindowPos] := S;
  FWindowPos := (FWindowPos + 1) mod DMR_SAMPLES_PER_SYM;
  if FWindowCount < DMR_SAMPLES_PER_SYM then Inc(FWindowCount);
  Inc(FSampleNo);
  if FWindowCount < DMR_SAMPLES_PER_SYM then Exit;

  // Ten interleaved timing hypotheses. Each receives one boxcar-integrated
  // symbol every ten input samples; the correct phase produces exact sync.
  Phase := Integer(FSampleNo mod DMR_SAMPLES_PER_SYM);
  Sym := FWindowSum / DMR_SAMPLES_PER_SYM;
  ProcessSymbol(Phase, Sym);
end;

procedure TDMRDecoder.ProcessSymbol(Phase: Integer; Symbol: Double);
var
  i: Integer;
  Pat: LongWord;
  Dibit: Byte;
  V: Double;
begin
  V := Symbol;
  if FInputInverted then V := -V;
  Dibit := Digitize(Phase, V);

  // Keep the 90 dibits ending at sync. Once the timing phase is selected this
  // supplies burst positions 0..89 without waiting for another frame.
  FDibitHistory[Phase, FHistoryPos[Phase]] := Dibit;
  FHistoryPos[Phase] := (FHistoryPos[Phase] + 1) mod (DMR_SYNC_END_DIBIT + 1);
  if FHistoryCount[Phase] < DMR_SYNC_END_DIBIT + 1 then Inc(FHistoryCount[Phase]);

  FMagSum[Phase] := FMagSum[Phase] - FMagHistory[Phase, FMagPos[Phase]] + Abs(V);
  FMagHistory[Phase, FMagPos[Phase]] := Abs(V);
  FMagPos[Phase] := (FMagPos[Phase] + 1) mod 24;

  if FTrackPhase = Phase then
  begin
    if FCurrentBurstPos < DMR_BURST_DIBITS then
    begin
      FCurrentBurst[FCurrentBurstPos] := Dibit;
      Inc(FCurrentBurstPos);
      if FCurrentBurstPos = DMR_BURST_DIBITS then CompleteBurst;
    end;
  end;

  FSyncShift[Phase] := ((FSyncShift[Phase] shl 1) and DMR_SYNC_MASK);
  if V < 0 then FSyncShift[Phase] := FSyncShift[Phase] or 1;

  for i := 0 to High(SYNC_TEXT) do
  begin
    Pat := SyncBits(SYNC_TEXT[i]);
    if FSyncShift[Phase] = Pat then
    begin
      NoteSync(Phase, SYNC_KIND[i], FInputInverted);
      Exit;
    end;
  end;
end;

function TDMRDecoder.Digitize(Phase: Integer; Symbol: Double): Byte;
var
  A, Threshold: Double;
begin
  A := Abs(Symbol);
  if FOuterLevel[Phase] <= 1.0e-9 then FOuterLevel[Phase] := A
  else if A > FOuterLevel[Phase] then
    FOuterLevel[Phase] := A
  else
    FOuterLevel[Phase] := FOuterLevel[Phase] + 0.001 * (A - FOuterLevel[Phase]);
  Threshold := 0.625 * FOuterLevel[Phase];
  if Symbol >= 0 then
  begin
    if A >= Threshold then Result := 1 else Result := 0; // +3 / +1
  end
  else
  begin
    if A >= Threshold then Result := 3 else Result := 2; // -3 / -1
  end;
end;

procedure TDMRDecoder.StartBurstTracking(Phase: Integer);
var
  i, P: Integer;
begin
  if FHistoryCount[Phase] < DMR_SYNC_END_DIBIT + 1 then Exit;
  FTrackPhase := Phase;
  P := FHistoryPos[Phase]; // oldest item; ring is exactly 90 dibits full
  for i := 0 to DMR_SYNC_END_DIBIT do
  begin
    FCurrentBurst[i] := FDibitHistory[Phase, P];
    P := (P + 1) mod (DMR_SYNC_END_DIBIT + 1);
  end;
  FCurrentBurstPos := DMR_SYNC_END_DIBIT + 1;
end;

procedure TDMRDecoder.CompleteBurst;
begin
  Move(FCurrentBurst[0], FLastBurst[0], SizeOf(FLastBurst));
  DMRParseBurst(FLastBurst, FLastBurstInfo);
  if FLastBurstInfo.SlotType.Valid and
     (FSyncKind in [dskBSData, dskMSData, dskDirectTS1Data,
      dskDirectTS2Data]) then
  begin
    FColorCodeValid := True;
    FColorCode := FLastBurstInfo.SlotType.ColorCode;
    FLastDataType := FLastBurstInfo.SlotType.DataType;
    FSlotTypeCorrectedBits := FLastBurstInfo.SlotType.CorrectedBits;
  end;
  if FLastBurstInfo.LinkControl.Decoded then
  begin
    if (FSyncKind in [dskBSData, dskBSVoice]) and
       FLastBurstInfo.CACH.Valid then
      FLastLCSlot := FLastBurstInfo.CACH.Slot
    else if FSyncKind in [dskDirectTS2Data, dskDirectTS2Voice] then
      FLastLCSlot := 1
    else
      FLastLCSlot := 0;
    FLinkControl[FLastLCSlot] := FLastBurstInfo.LinkControl;
    if FSelectedSlot < 0 then
    begin
      FSelectedSlot := FLastLCSlot;
      FLastSelectedVoiceTick := GetTickCount64;
    end;
  end;
  DecodeVoiceBurst;
  Inc(FBurstCount);
  FCurrentBurstPos := 0;
end;

procedure TDMRDecoder.DecodeVoiceBurst;
var
  Frames: TDMRAMBEFrames;
  PCM: array[0..DMR_PCM_SAMPLES - 1] of Single;
  MbeResult: TDMRMbeResult;
  Slot, FrameIndex, RC: Integer;
  NowTick: QWord;
begin
  if (FMbe = nil) or (FLastSyncTick = 0) or
     (GetTickCount64 - FLastSyncTick > DMR_SYNC_HOLD_MS) then Exit;
  if not (FSyncKind in [dskBSVoice, dskMSVoice, dskDirectTS1Voice,
          dskDirectTS2Voice]) then Exit;

  if FSyncKind in [dskBSVoice] then
  begin
    if not FLastBurstInfo.CACH.Valid then Exit;
    Slot := FLastBurstInfo.CACH.Slot;
  end
  else if FSyncKind = dskDirectTS2Voice then Slot := 1
  else Slot := 0;
  NowTick := GetTickCount64;
  if (FSelectedSlot < 0) or
     ((Slot <> FSelectedSlot) and (FLastSelectedVoiceTick <> 0) and
      (NowTick - FLastSelectedVoiceTick > 1000)) then
  begin
    FSelectedSlot := Slot;
    DMRMbeReset(FMbe);
  end;
  if Slot <> FSelectedSlot then Exit;
  FLastSelectedVoiceTick := NowTick;
  // Service Options bit 6 denotes privacy/encryption. mbelib cannot decrypt
  // it, so suppress the characteristic digital noise while retaining IDs.
  if FLinkControl[Slot].Decoded and
     ((FLinkControl[Slot].ServiceOptions and $40) <> 0) then Exit;

  DMRExtractAMBEFrames(FLastBurst, Frames);
  for FrameIndex := 0 to 2 do
  begin
    FillChar(MbeResult, SizeOf(MbeResult), 0);
    RC := DMRMbeDecode(FMbe, @Frames[FrameIndex][0], @PCM[0], @MbeResult);
    if RC <> 0 then
    begin
      Inc(FVoiceErrorCount);
      Continue;
    end;
    Inc(FVoiceFrameCount);
    if MbeResult.ErrorsTotal > 0 then Inc(FVoiceErrorCount, MbeResult.ErrorsTotal);
    if Assigned(FOnAudio) then FOnAudio(PCM, Length(PCM));
  end;
end;

procedure TDMRDecoder.NoteSync(Phase: Integer; Kind: TDMRSyncKind;
  Inverted: Boolean);
var
  NowTick: QWord;
begin
  NowTick := GetTickCount64;
  FStatusLock.Enter;
  try
    // Adjacent timing hypotheses recognize the same physical burst within one
    // sample period. Keep the phase with the largest 24-symbol eye opening,
    // not merely the first phase that happened to match the sign pattern.
    if (FLastSyncTick <> 0) and (NowTick - FLastSyncTick < 5) then
    begin
      if FMagSum[Phase] > FBestSyncQuality then
      begin
        FBestSyncQuality := FMagSum[Phase];
        FSyncKind := Kind;
        FInverted := Inverted;
        StartBurstTracking(Phase);
      end;
      Exit;
    end;
    FSyncKind := Kind;
    FInverted := Inverted;
    Inc(FSyncCount);
    FLastSyncTick := NowTick;
    FBestSyncQuality := FMagSum[Phase];
    StartBurstTracking(Phase);
  finally
    FStatusLock.Leave;
  end;
end;

procedure TDMRDecoder.GetStatus(out S: TDMRStatus);
var
  NowTick: QWord;
  LCStatusSlot: Integer;
begin
  FillChar(S, SizeOf(S), 0);
  NowTick := GetTickCount64;
  FDSPLock.Enter;
  try
    FStatusLock.Enter;
    try
      S.Enabled := FEnabled;
      S.SyncKind := FSyncKind;
      S.Inverted := FInverted;
      S.SyncCount := FSyncCount;
      S.BurstCount := FBurstCount;
      S.BurstDibits := FCurrentBurstPos;
      if FLastSyncTick <> 0 then S.LastSyncAgeMs := NowTick - FLastSyncTick
      else S.LastSyncAgeMs := High(QWord);
      S.Synced := FEnabled and (FLastSyncTick <> 0) and
                  (S.LastSyncAgeMs <= DMR_SYNC_HOLD_MS);
      S.SignalRMS := Sqrt(FRMSSq);
      S.VocoderAvailable := FMbe <> nil;
      // CACH exists on base-station bursts. On MS/direct bursts the same
      // positions are payload/guard symbols and can accidentally form a
      // syntactically valid Hamming word.
      S.CACHValid := FLastBurstInfo.CACH.Valid and
                     (FSyncKind in [dskBSData, dskBSVoice]);
      S.Slot := FLastBurstInfo.CACH.Slot;
      S.LCSS := FLastBurstInfo.CACH.LCSS;
      // Voice sync replaces the centre Slot Type field. Do not expose a
      // chance Golay match from AMBE bits as a real colour/data type.
      S.SlotTypeValid := FColorCodeValid;
      S.ColorCode := FColorCode;
      S.DataType := FLastDataType;
      S.SlotTypeCorrectedBits := FSlotTypeCorrectedBits;
      LCStatusSlot := FSelectedSlot;
      if (LCStatusSlot < 0) or not FLinkControl[LCStatusSlot].Decoded then
        LCStatusSlot := FLastLCSlot;
      S.LinkControlValid := (LCStatusSlot >= 0) and
                            FLinkControl[LCStatusSlot].Decoded;
      S.LCSlot := LCStatusSlot;
      if S.LinkControlValid then
      begin
        S.LCOpcode := FLinkControl[LCStatusSlot].Opcode;
        S.ServiceOptions := FLinkControl[LCStatusSlot].ServiceOptions;
        S.TargetID := FLinkControl[LCStatusSlot].TargetID;
        S.SourceID := FLinkControl[LCStatusSlot].SourceID;
      end;
      S.SelectedSlot := FSelectedSlot;
      S.VoiceFrameCount := FVoiceFrameCount;
      S.VoiceErrorCount := FVoiceErrorCount;
    finally
      FStatusLock.Leave;
    end;
  finally
    FDSPLock.Leave;
  end;
  FRingLock.Enter;
  try
    S.DroppedSamples := FDropped;
  finally
    FRingLock.Leave;
  end;
end;

function TDMRDecoder.GetLastBurst(var Dibits: array of Byte;
  out Sequence: QWord): Boolean;
var
  N: Integer;
begin
  Sequence := 0;
  FDSPLock.Enter;
  try
    Result := FBurstCount <> 0;
    if not Result then Exit;
    N := Min(Length(Dibits), DMR_BURST_DIBITS);
    if N > 0 then Move(FLastBurst[0], Dibits[0], N * SizeOf(Byte));
    Sequence := FBurstCount;
  finally
    FDSPLock.Leave;
  end;
end;

class function TDMRDecoder.SyncKindName(Kind: TDMRSyncKind): string;
begin
  case Kind of
    dskBSData: Result := 'BS data';
    dskBSVoice: Result := 'BS voice';
    dskMSData: Result := 'MS data';
    dskMSVoice: Result := 'MS voice';
    dskDirectTS1Data: Result := 'direct TS1 data';
    dskDirectTS1Voice: Result := 'direct TS1 voice';
    dskDirectTS2Data: Result := 'direct TS2 data';
    dskDirectTS2Voice: Result := 'direct TS2 voice';
  else
    Result := 'none';
  end;
end;

end.