I Need To Keep Sending 5 Bytes Of Data Repeatedly To Check Some Readings,So Where Do I Place My While Loop So That The Data Is Continously Sent

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C++

#include <windows.h>
#include <stdio.h>


int main()
{

    // Defining hexadecimal bytes
    int bytes_to_send[5];
    bytes_to_send[0] = 0x81;
    bytes_to_send[1] = 0x11;
    bytes_to_send[2] = 0xF1;
    bytes_to_send[3] = 0x11;
    bytes_to_send[4] = 0x04;

// Declare variables and structures
    HANDLE hSerial;
    DCB dcbSerialParams = {0};
    COMMTIMEOUTS timeouts = {0};

    // Open the highest available serial port number
    fprintf(stderr, "Opening serial port...");
    hSerial = CreateFile(
                "COM4", GENERIC_READ|GENERIC_WRITE, 0, NULL,
                OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL );
    if (hSerial == INVALID_HANDLE_VALUE)
    {
            fprintf(stderr, "Error\n");
            return 1;
    }
    else fprintf(stderr, "OK\n");

    // Set device parameters (10400 baud, 1 start bit,
    // 1 stop bit, no parity)
    dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
    if (GetCommState(hSerial, &dcbSerialParams) == 0)
    {
        fprintf(stderr, "Error getting device state\n");
        CloseHandle(hSerial);
        return 1;
    }

    dcbSerialParams.BaudRate = 10400;
    dcbSerialParams.ByteSize = 8;
    dcbSerialParams.StopBits = ONESTOPBIT;
    dcbSerialParams.Parity = NOPARITY;
    if(SetCommState(hSerial, &dcbSerialParams) == 0)
    {
        fprintf(stderr, "Error setting device parameters\n");
        CloseHandle(hSerial);
        return 1;
    }

    // Set COM port timeout settings
    timeouts.ReadIntervalTimeout = 50;
    timeouts.ReadTotalTimeoutConstant = 50;
    timeouts.ReadTotalTimeoutMultiplier = 10;
    timeouts.WriteTotalTimeoutConstant = 50;
    timeouts.WriteTotalTimeoutMultiplier = 10;
    if(SetCommTimeouts(hSerial, &timeouts) == 0)
    {
        fprintf(stderr, "Error setting timeouts\n");
        CloseHandle(hSerial);
        return 1;
    }

    // Send specified text (remaining command line arguments)
    DWORD bytes_written, total_bytes_written = 0;
    fprintf(stderr, "sending bytes...");
    
    if(!WriteFile(hSerial, bytes_to_send, 5, &bytes_written, NULL))
    {
        fprintf(stderr, "Error\n");
        CloseHandle(hSerial);
        return 1;
    }
    fprintf(stderr, "%d bytes written\n", bytes_written);



    // Close serial port
    fprintf(stderr, "Closing serial port...");
    if (CloseHandle(hSerial) == 0)
    {
        fprintf(stderr, "Error\n");
        return 1;
    }
    fprintf(stderr, "OK\n");

    // exit normally
    return 0;
}

[EDIT: Added code formatting, Jochen Arndt]

Posted 19-Mar-15 3:52am

vinod b v

Updated 19-Mar-15 4:29am

Jochen Arndt

v2

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Jochen Arndt · Accepted Answer · 2015-03-19T04:22:00

This depends on your type of application. If you are going to create a GUI application or need to perform other tasks, you must use a worker thread or overlapped I/O.

Your current implementation uses a blocking write call. This means that the call will not return until all data has been send or a timeout occurs. During this time your application can not perform other tasks like processing user input.

For a simple console test program you can just put the write calls into a while loop that breaks upon errors or key press (include conio.h and use _kbit() followed by a _getch() call when a key was pressed).

I suggest to use the above simple method at least until the communication is working.

[EDIT: Added example]

C++

int GetPressedKey()
{
    int ret = 0;
    if (_kbhit())
    {
        ret = _getch();
    }
    return ret;
}

// Code to write and read inside a loop
while (1)
{
    if (!WriteFile(hSerial, bytes_to_send, 5, &bytes_written, NULL))
        break;
    fprintf(stderr, "%d bytes written\n", bytes_written);
    if (GetPressedKey())
        break;
    // Read data here
    if (GetPressedKey())
        break;
}
CloseHandle(hSerial);