How to understand if data comes to serialport buffer

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need to receive data from serialport. I wrote a program with Windows.h library, using C++, Visual Studio 2010..

I receive all datas from an electronic card, we communicate by handshaking...

I've made the necessary adjustments for handshaking as shown below:

DCB dcb;

dcb.ByteSize = 8;
dcb.Parity = NOPARITY;
dcb.StopBits = ONESTOPBIT;
dcb.fOutxCtsFlow = TRUE;
dcb.fOutxDsrFlow = TRUE;
dcb.fBinary = TRUE;
dcb.fParity = FALSE;
dcb.fNull = FALSE;
dcb.fOutX = FALSE;
dcb.fInX =  FALSE;

Then I set RTS and DTR bits to say I'm ready to receive data as shown below. This one is the function I call:

bool ImSeriAygit::setHardwareControl(bool hardwareControl)
{
    DCB dcb;

    myHardwareControl = hardwareControl;

    if (getStatus() != STATUS_OPEN) // if closed
        return true;

    if (!GetCommState(myPort, &dcb)) // Default port
    {
        printf("ImSeriAygit::setHardwareControl: Could not get port Data.\n");
        return false;
    }

    if(myHardwareControl == 0) /* set control lines */
    {
        dcb.fRtsControl = RTS_CONTROL_ENABLE; // Enable RTS 
        dcb.fDtrControl = DTR_CONTROL_ENABLE; // Enable DTR
    }

    else
    {
        dcb.fRtsControl = RTS_CONTROL_DISABLE; // rts disable
        dcb.fDtrControl = DTR_CONTROL_DISABLE; // dtr disable
    }

    if (!SetCommState(myPort, &dcb)) 
    {  
        printf("ImSeriAygit::setHardwareControl: Could not set port Data.\n");
        return false;
    }  

  return true;
}

This is how I call it:

ser.setHardwareControl(false); // ser is the ImSeriAygit object.
After that I read the serial port using ReadFile function as shown below:

int ImSeriAygit::read(const char *data, unsigned int size, 
                      unsigned int msWait) 
{
    COMSTAT stat;

    unsigned long ret;
    unsigned int numToRead;

    if (myPort != INVALID_HANDLE_VALUE && myStatus == STATUS_OPEN)
    {
        if (!ClearCommError(myPort, &ret, &stat)) 
            return -1;

        if (stat.cbInQue == 0) 
            return 0;

        if (stat.cbInQue > size) 
            numToRead = size;
        else
            numToRead = stat.cbInQue;

        if(get

        if (ReadFile( myPort, (void *)data, numToRead, &ret, NULL))
        {
            return (int)ret;
        }
        else 
        {
            printf("ArSerialConnection::read:  Read failed.\n");
            return -1;
        }
    }

    printf("ArSerialConnection::read: Connection invalid.\n");
    return -1;
}

When I debug my program, I realised that sometimes the data I read is corrupted, which is in fact in a suitable form, but sometimes there is no corruption...

I guess I don't catch the incoming data properly although I'm handshaking...

Any suggestions to know if the data comes in time? My best regards...

Posted 10-Feb-12 3:13am

Un_NaMeD

Updated 10-Feb-12 4:23am

v2

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Jochen Arndt · Accepted Answer · 2012-02-10T04:18:00

You are calling ClearCommError() but did not check the error value. Maybe that will help you finding the problem.

You are checking if there are more bytes available than your buffer can hold. That's good. But if this happens, you should call the receive function again immediately.

You are probably comparing a boolean value with 0 and uses reversed logic:

C++

// Parameter hardwareControl is bool
bool ImSeriAygit::setHardwareControl(bool hardwareControl)
{
...
// Copy parameter to member var. Really necessary? 
// Is myHardwareControl also of type bool?
    myHardwareControl = hardwareControl;
...
// Compare a boolean value (or is myHardwareControl of type int or other?)
//  with 0. Using 'false' would be better.
// But this is reversed logic: Setting control lines when value is false.
    if(myHardwareControl == 0) /* set control lines */

You did not show that you are toggling DTR and RTS later, thus signaling the other end that you are always ready to receive data. This can result in data loss when the receive buffer is full. This may even happen with rather slow serial communication when the system load is high (e.g. disk and network transfers). You may use RTS_CONTROL_HANDSHAKE and DTR_CONTROL_HANDSHAKE to avoid buffer overruns.

If the connected system is not only responding to requests, but sending data by itself, you should create a worker thread for receiving data using overlapped IO.