synapse库中的wsaetimedout消息

为什么此代码中总是出现wsaetimedout错误:

var fUDPBuf: array [1..UdpPacketSize] of byte;
{...}
UDPSocket := TUDPBlockSocket.Create;
UDPSocket.Bind(UDPIP, UDPPort);
if UDPSocket.LastError = 0 then
  Raise EDevFail.Create(Format(SPortFailed, [UDPPort]));

while not Terminated do begin
  BytesRead := UDPSocket.RecvBufferEx(@fUDPBuf[1], UdpPacketSize, 1000);
  if BytesRead <= 0 then
    case UDPSocket.LastError of
      0, WSAETIMEDOUT: Continue;
      WSAECONNRESET, WSAENETRESET,
      WSAENOTCONN, WSAECONNABORTED,
      WSAENETDOWN: begin
                     Raise EDevFail.Create(UDPSocket.GetErrorDesc(UDPSocket.LastError));
                     UDPSocket.CloseSocket;
                   end;
      else begin
        Raise EDevFail.Create(UDPSocket.GetErrorDesc(UDPSocket.LastError));
        UDPSocket.CloseSocket;
      end;
    end;

  //Sleep(1);
  ProcessData(@fUDPBuf[1]);
  inc(PacketCount);
end;

我确信我从网络设备接收到的udp数据和udppacketsize一样多。