Re: Reading Serial Port

From:
clinisbut <clinisbut@gmail.com>
Newsgroups:
microsoft.public.vc.mfc
Date:
Wed, 30 Jan 2008 03:37:48 -0800 (PST)
Message-ID:
<5edcd8e2-2a6c-4276-aade-844e41317c6f@s12g2000prg.googlegroups.com>
On Jan 30, 11:50 am, clinisbut <clinis...@gmail.com> wrote:

After reading a lot about threads, now I can understand the example
fromhttp://www.flounder.com/serial.htm.

I need to comunicate with a device that I tested and works OK, it just
sends frames at 9600 bauds (other programs receive their frames as
expected).

In my firsts attempts I was receiving corrupted frames, but I think I
corrected it adjusting the dcb to:
dcb.DCBlength = sizeof(dcb);
  dcb.BaudRate = CBR_9600;
  dcb.fBinary = TRUE;
  dcb.fParity = TRUE;
  dcb.fOutxCtsFlow = FALSE;
  dcb.fOutxDsrFlow = FALSE;
  dcb.fDtrControl = DTR_CONTROL_DISABLE;
  dcb.fDsrSensitivity = FALSE;
  dcb.fTXContinueOnXoff = FALSE;
  dcb.fOutX = FALSE;
  dcb.fInX = FALSE;
  dcb.fErrorChar = FALSE;
  dcb.fNull = FALSE;
  dcb.fRtsControl = RTS_CONTROL_DISABLE;
  dcb.fAbortOnError = FALSE;
  dcb.XonLim = 2048; //I think just a 0 will work,
so I have all flow controls at false
  dcb.XoffLim = 512; //I think just a 0 will
work, so I have all flow controls at false
  dcb.ByteSize = 8;
  dcb.Parity = ODDPARITY;
  dcb.StopBits = 0;
  dcb.XonChar = 0;
  dcb.XoffChar = 0;
  dcb.ErrorChar = 0;
  dcb.EofChar = 0;
  dcb.EvtChar = 0;

Ok, mostly all corrupted bytes dissapeared.
This is the frame I should receive (16 bytes length):
af 0a 00 00 00 00 00 00 00 00 00 00 00 00 00 b9

My first problem comes with a curious fact:
I always get the frame 16th cutted!!
Sometimes I just receive its last byte (b9), or some middle 0x00
ommited... other times af and 0a with some 0's...

Example:

af 0a 00 00 00 00 00 00 00 00 00 00 00 00 00 b9 //15th frame
00 00 b9 //
16th frame
af 0a 00 00 00 00 00 00 00 00 00 00 00 00 00 b9 //17th frame

What's wrong??? I found that 256/16 (bytes) = 16 frames. Is this
casual?? Note that this only happens in frame 16th, no error with
frame number 32 or other.
Here my reader handler where I read single bytes every loop:

void MyThread::OnReadData( WPARAM wParam, LPARAM )
{
        BOOL reading = TRUE;
        DWORD dwError = 0;
        DWORD bytesRead;
        COMSTAT comState;
        HANDLE hArray[2]; //Un array de eventos
        hArray[0] = ShutdownEvent;
        hArray[1] = ovReader.hEvent;

        //Extrae el estado del puerto y limpia el flag de error para
siguientes operaciones I/O
        ClearCommError( hComm, &dwError, &comState );

        while( reading )
        {
                unsigned char buffer;

                BOOL ok = ::ReadFile( hComm, &buffer, 1, &bytesRead, &ovReader );
                if( !ok ) //ERROR
                {
                        DWORD err = GetLastError();
                        if( err!=ERROR_IO_PENDING )
                        {
                                TRACE("Error lectura.\n");
                                reading = FALSE;
                                continue; //Nos saltamos el switch
                        }

                        //Ahora esperamos a que ocurra Shutdown o ovReader
                        DWORD result = WaitForMultipleObjects( 2, hArray, FALSE,
INFINITE );
                        switch( result )
                        {
                                //Esperar
                                case WAIT_OBJECT_0: //Shutdown
                                                                TRACE("SHUTDOWN!\n");
                                                                reading = FALSE;
                                                                continue;

                                case WAIT_OBJECT_0+1: // I/O complete!
                                                                //TRACE("DATA RECEIVED!.\n");
                                                                ok = GetOverlappedResult( hComm, &ovReader, &bytesRead,
TRUE );
                                                                if(!ok )
                                                                {
                                                                        TRACE( "ERROR getoverlapped result.\n");
                                                                        reading = FALSE;
                                                                        continue;
                                                                }
                                                                else
                                                                {
                                                                        TRACE( "Received with delay: bytesRead:%d buffer:%d
\n",bytesRead, buffer);
                                                                }
                                                                break;
                        }
                }
                else
                {
                        TRACE("\nOK==TRUE -->bytesRead:%d buffer:%d\n",bytesRead, buffer);
                }

                if( bytesRead>0 )
                {
                        this->notificador->PostMessage(UWM_DATA_READ, (WPARAM)buffer);
                }
                else //Nothing readed
                        continue;
                }

}


If you are wondering why I'm reading justa a byte each time when all
frames are 16 bytes length it's because this is just a test, in the
final version the device will send variable frame lengths.

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