SetCommState Fails?

[Tony Glader]

Hello!

Com0com serial port baudrate can't be set with SetCommState(). It fails with error 'The Parameter is incorrect'. Why?

Here is source:

      dcbCommPort.DCBlength = sizeof(DCB);
      GetCommState(hComm, &dcbCommPort);

      dcbCommPort.BaudRate = BAUD_19200;
      dcbCommPort.Parity = NOPARITY;
      dcbCommPort.ByteSize = 8;
      dcbCommPort.StopBits = ONESTOPBIT;
      dcbCommPort.fDtrControl = DTR_CONTROL_DISABLE;
      dcbCommPort.fRtsControl = RTS_CONTROL_DISABLE;
   
   
      if(!SetCommState(hComm, &dcbCommPort))
      {
       void *lpMsgBuf;
       FormatMessage(
            FORMAT_MESSAGE_ALLOCATE_BUFFER |
            FORMAT_MESSAGE_FROM_SYSTEM |
            FORMAT_MESSAGE_IGNORE_INSERTS,
            NULL,
            GetLastError(),
            0,
            (LPTSTR) &lpMsgBuf,
            0, NULL );
   
         MessageBox(NULL, (LPTSTR)lpMsgBuf, NULL, MB_OK | MB_ICONINFORMATION);
   
         StatusBox->Lines->Add("Cannot set comm state.");
         CloseHandle(hComm);
         hComm = NULL;
         return;
      }

[Vyacheslav Frolov]

You code works on my PC.

Anyway

1. Add `if (hComm == INVALID_HANDLE_VALUE) …`
2. Add `if (!GetCommState( …`
3. Replace `BAUD_19200` by `CBR_19200`
4. Replace `hComm = NULL` by `hComm = INVALID_HANDLE_VALUE`

[Tony Glader]

Added check of GetCommState and it fails also:

         DCB dcbCommPort;
      void *lpMsgBuf;
   
      StatusBox->Lines->Add("Connecting..");
      if(hComm != NULL)
      {
       StatusBox->Lines->Add("Already connected");
       return;
      }
   
   
   
      hComm = CreateFile("COM19",
                          GENERIC_READ | GENERIC_WRITE,
                          0,
                          0,
                          OPEN_ALWAYS,
                          0,
                          0);
   
      // IF THE PORT CANNOT BE OPENED, BAIL OUT.
   
      if(hComm == INVALID_HANDLE_VALUE)
      {
       StatusBox->Lines->Add("Connection failed!");
       return;
      }
   
      StatusBox->Lines->Add("Connected");
   
   
      GetCommTimeouts(hComm,&ctmoOld);
      ctmoNew.ReadTotalTimeoutConstant = 100;
      ctmoNew.ReadTotalTimeoutMultiplier = 0;
      ctmoNew.WriteTotalTimeoutMultiplier = 0;
      ctmoNew.WriteTotalTimeoutConstant = 0;
      SetCommTimeouts(hComm, &ctmoNew);
   
      dcbCommPort.DCBlength = sizeof(DCB);
   
      if(!GetCommState(hComm, &dcbCommPort))
      {
           FormatMessage(
            FORMAT_MESSAGE_ALLOCATE_BUFFER |
            FORMAT_MESSAGE_FROM_SYSTEM |
            FORMAT_MESSAGE_IGNORE_INSERTS,
            NULL,
            GetLastError(),
            0,
            (LPTSTR) &lpMsgBuf,
            0, NULL );
   
         MessageBox(NULL, (LPTSTR)lpMsgBuf, NULL, MB_OK | MB_ICONINFORMATION);
   
         StatusBox->Lines->Add("Cannot get comm state.");
         CloseHandle(hComm);
         hComm = INVALID_HANDLE_VALUE;
         return;
   
      }
   
      dcbCommPort.BaudRate = CBR_19200;
      dcbCommPort.Parity = NOPARITY;
      dcbCommPort.ByteSize = 8;
      dcbCommPort.StopBits = ONESTOPBIT;
      dcbCommPort.fDtrControl = DTR_CONTROL_DISABLE;
      dcbCommPort.fRtsControl = RTS_CONTROL_DISABLE;
   
   
      if(!SetCommState(hComm, &dcbCommPort))
      {
       FormatMessage(
            FORMAT_MESSAGE_ALLOCATE_BUFFER |
            FORMAT_MESSAGE_FROM_SYSTEM |
            FORMAT_MESSAGE_IGNORE_INSERTS,
            NULL,
            GetLastError(),
            0,
            (LPTSTR) &lpMsgBuf,
            0, NULL );
   
         MessageBox(NULL, (LPTSTR)lpMsgBuf, NULL, MB_OK | MB_ICONINFORMATION);
   
         StatusBox->Lines->Add("Cannot set comm state.");
         CloseHandle(hComm);
         hComm = INVALID_HANDLE_VALUE;
         return;

[Vyacheslav Frolov]

You have created a regular file COM19 in the working directory.

Shold be

    hComm = CreateFile("\\\\.\\COM19",
                       GENERIC_READ|GENERIC_WRITE,
                       0,
                       NULL,
                       OPEN_EXISTING,
                       0,
                       NULL);

[Tony Glader]

Thanks! That was solution :). Now just WriteFile raises exception, but that is another problem not related to com0com, i guess.