reading from USB port using mex code .. the DLL is taking more time and less time in constently

    h = CreateFile(portname,
                   GENERIC_READ | GENERIC_WRITE,
                   0, NULL,
                   OPEN_EXISTING, 0, NULL);

    if (h == INVALID_HANDLE_VALUE) 
    {
        mexPrintf("\n\n !! FAILED TO OPEN PORT %s\n\n", portname);
        return -1;
    }

    dcb.DCBlength = sizeof(dcb);
    dcb.BaudRate  = 57600;
    dcb.fBinary   = 1;
    dcb.Parity    = NOPARITY;
    dcb.StopBits  = ONESTOPBIT;
    dcb.ByteSize  = 8;

    if (!SetCommState(h, &dcb)) 
    {
        mexPrintf("\n\n SetCommState Failed\n\n");
        return -1;
    }
    /* Will print hex values of received bytes */
    for (i = 0; i < imax; i++) 
    {
        /* Wait for characters */
        read = 0;
        while(!read) 
        {
            ReadFile(h, &ch, 1, &read, NULL);
            if (read) Data[i] = ch;
        }
     }

    CloseHandle(h);
    mexPrintf("Reading from USB Completed\n");

[Jan]

You forgot to ask a question. The DLL is taking more time and less time (simultaneously?!) than what?