通过串口(COM)实现无重叠通信的正确方法

Question

我正在使用德尔福XE2，我试图通过串口与一些设备通信。沟通应该是直接的，但我有一些问题。设备通信协议如下:I(主)发送帧，以":“开头，以CRLF结束。设备(从)以相同的格式发送响应(以":“开头，以CRLF结尾)。

我正在使用WinAPI和不重叠的IO。我遇到的问题是，我经常从设备接收#0字符作为响应。我确信问题就在我这一边，因为我可以使用设备提供者应用程序，而且我可以看到通信进行得很好。

下面是我如何设置COM端口：

Result := False;
FFileHandle := CreateFile('COM3', GENERIC_READ OR GENERIC_WRITE, 0, nil, OPEN_EXISTING, 0, 0);
if FFileHandle = INVALID_HANDLE_VALUE then
  Exit;

if not GetCommState(FFileHandle, DCB) then
  Exit;
DCB.BaudRate := ASettings.BaudRate;
DCB.Flags := 1 OR // BINARY
             (DTR_CONTROL_ENABLE shl 4) OR
             (RTS_CONTROL_ENABLE shl 12);

DCB.XonLim := 100;           // transmit XON threshold
DCB.XoffLim := 100;          // transmit XOFF threshold
DCB.ByteSize := 8;           // number of bits/byte, 4-8
DCB.Parity := 0;             // 0-4=no,odd,even,mark,space
DCB.StopBits := ONESTOPBIT;  // 0,1,2 = 1, 1.5, 2
DCB.XonChar := #1;           // Tx and Rx XON character
DCB.XoffChar := #2;          // Tx and Rx XOFF character
DCB.ErrorChar := #$FF;       // error replacement character
DCB.EofChar := #$0A;         // end of input character
DCB.EvtChar := #$0A;         // received event character
if not SetCommState(FFileHandle, DCB) then
  Exit;
if not SetCommMask(FFileHandle, EV_RXCHAR OR EV_TXEMPTY OR EV_RXFLAG) then
  Exit;
Timeouts.ReadIntervalTimeout := 1200;
Timeouts.ReadTotalTimeoutMultiplier := 1;
Timeouts.ReadTotalTimeoutConstant := 1200;
Timeouts.WriteTotalTimeoutMultiplier := 0;
Timeouts.WriteTotalTimeoutConstant := 0;
if not SetCommTimeouts(FFileHandle, Timeouts) then
  Exit;
if not PurgeComm(FFileHandle, PURGE_TXABORT OR PURGE_RXABORT OR PURGE_TXCLEAR OR PURGE_RXCLEAR) then
  Exit;
if not ClearCommError(FFileHandle, Errors, @ComStat) then
  Exit;
if not SetupComm(FFileHandle, 1024, 1024) then
  Exit;
Result := True;

我是这样写的：

function TCOMPortWrapper.Write(const AFrame: AnsiString): TComPortWriteRes;
var
  Written: Cardinal;
  Err: Cardinal;
  Stat: TComStat;
  Mask: Cardinal;
begin
  Result := CPW_ERROR;
  ClearCommError(FFileHandle, Err, @Stat);
  if not IsOpened then
    Exit;
  if not WriteFile(FFileHandle, AFrame[1], Length(AFrame), Written, nil) then
    Exit;
  Mask := EV_TXEMPTY;
  if not WaitCommEvent(FFileHandle, Mask, nil) then
    Exit;
  ClearCommError(FFileHandle, Err, @Stat);
  Result := CPW_OK;
end;

最后，我是这样读到的：

function TCOMPortWrapper.Read(out Frame: AnsiString): TComPortReadRes;
var
  S: AnsiString;
  BytesRead: Cardinal;
  Mask: Cardinal;
begin
  Result := CPR_ERROR;
  if not IsOpened then
    Exit;
  SetLength(S, 4096);
  Mask := EV_RXFLAG;
  if not WaitCommEvent(FFileHandle, Mask, nil) then
    Exit;
  if not ReadFile(FFileHandle, S[1], Length(S), BytesRead, nil) then
    Exit;
  SetLength(S, BytesRead);
  Frame := S;
  Result := CPR_OK;
end;

正如我前面提到的，在读取中，我得到的不是实际的框架，而是#0字符的字符串。我认为，我的错误可能是在WaitCommEvent API调用，因为我是非常新的串行通信。

谢谢你帮忙！

Answer 1

也许你忘记了"@"：ReadFile(FFileHandle，@ S1，Length(S)，BytesRead，0)

我这样做是为了读COM中的字符串：

constructor TSerialPort.Create(const APortName: String);
begin
  inherited Create;

  FPortHandle := INVALID_HANDLE_VALUE;

  FPortName := APortName;

  FDCB.DCBlength := SizeOf(DCB);
  FDCB.BaudRate := CBR_19200;
  FDCB.Flags := MakeCommFlags(True, False, True, True, DTR_CONTROL_DISABLE,
    False, False, False, False, False, False, RTS_CONTROL_DISABLE, False);
  FDCB.wReserved := 0;
  FDCB.XonLim := 2048;
  FDCB.XoffLim := 512;
  FDCB.ByteSize := 8;
  FDCB.Parity := NOPARITY;
  FDCB.StopBits := ONESTOPBIT;
  FDCB.XonChar := #0;
  FDCB.XoffChar := #0;
  FDCB.ErrorChar := #0;
  FDCB.EofChar := #255;
  FDCB.EvtChar := #0;
  FDCB.wReserved1 := 0;

  FCTO.ReadIntervalTimeout := 0;
  FCTO.ReadTotalTimeoutMultiplier := 20;
  FCTO.ReadTotalTimeoutConstant := 500;
  FCTO.WriteTotalTimeoutMultiplier := 10;
  FCTO.WriteTotalTimeoutConstant := 200;

  FEOSChar := #13;
end;

function TSerialPort.Open: Boolean;
begin
  Result := False;
  if FPortHandle <> INVALID_HANDLE_VALUE then
    Close;

  FPortHandle := CreateFile(PChar('\\.\'+FPortName), GENERIC_READ or GENERIC_WRITE, 0,
    nil, OPEN_EXISTING, 0, 0);

  if FPortHandle <> INVALID_HANDLE_VALUE then
  begin
    // setup device buffers
    SetupComm(FPortHandle, 2048, 2048);

    Flush; // purge any information in the buffer

    Result := True;
  end;
end;


function TSerialPort.ReadString(var S: SysUtils.TBytes): Boolean;
const
  MAX_BUF = 255;
var
  B: Byte;
  iCounter: Integer;
begin
  Result := True;
  B := 0;

  SetLength(S, MAX_BUF);
  ZeroMemory(@S[0], Length(S));
  iCounter := 0;

  while (B <> Ord(FEOSChar)) and Result and (iCounter < MAX_BUF) do
  begin
    Result := Read(B, 1);

    if (B <> Ord(FEOSChar)) and Result then
    begin
      S[iCounter] := B;
      Inc(iCounter);
    end;
  end;

  if Result then
  begin // delete leading zeros
    while (Length(S) > 0) and (S[0] = 0) do
    begin
      for iCounter := 0 to Length(S)-2 do
        S[iCounter] := S[iCounter+1];
      SetLength(S,Length(S)-1);
    end;
  end
  else
    SetLength(S, 0);
end;

function TSerialPort.Read(var inbuf; inlen: DWORD): Boolean;
var
  dwBytesRead: DWORD;
begin
  Result := False;
  if FPortHandle = INVALID_HANDLE_VALUE then
    Exit;

  dwBytesRead := 0;
  Result := ReadFile(FPortHandle, inbuf, inlen, dwBytesRead, nil);
end;

字符串字节/char的FEOSChar结束。要从string获得TBytes，可以使用SysUtils.StringOf()函数

upd：

function MakeCommFlags(fBinary, fParity, fOutxCtsFlow, fOutxDsrFlow: Boolean;
  fDtrControl: Byte; fDsrSensitivity, fTXContinueOnXoff, fOutX, fInX,
  fErrorChar, fNull: Boolean; fRtsControl: Byte;
  fAbortOnError: Boolean): DWORD;
begin
  Result := 0;

  fDtrControl := fDtrControl and $03;
  fRtsControl := fRtsControl and $03;

  Result := Result or (Byte(fBinary) shl 0);
  Result := Result or (Byte(fParity) shl 1);
  Result := Result or (Byte(fOutxCtsFlow) shl 2);
  Result := Result or (Byte(fOutxDsrFlow) shl 3);
  Result := Result or (Byte(fDtrControl) shl 4);
  Result := Result or (Byte(fDsrSensitivity) shl 6);
  Result := Result or (Byte(fTXContinueOnXoff) shl 7);
  Result := Result or (Byte(fOutX) shl 8);
  Result := Result or (Byte(fInX) shl 9);
  Result := Result or (Byte(fErrorChar) shl 10);
  Result := Result or (Byte(fNull) shl 11);
  Result := Result or (Byte(fRtsControl) shl 12);
  Result := Result or (Byte(fAbortOnError) shl 14);
end;