Writing and reading from a serial port

[niksready]

Hello,

I am working on a project that will basically write some data to 8250 serial port (/dev/ttyS0) and then read back the same data. My understanding is if I write something, it will stored in a buffer and then if I read back, I should be able to read what I just wrote. However, I am having issues where I can write successfully to a serial port but when I check for # of bytes available in the input buffer, it returns 0. So basically, my write does not flush. Can you tell me where the problem..? Here is my code snippet.

#include <termios.h>
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/signal.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <stdlib.h>
#include <sys/ioctl.h>

int main()
{
    int fd, res, sen;
    int i;
    struct termios oldtio, newtio;
    char buf[] = "hello";
    int bytes, total;
	
	 fd = open("/dev/ttyS0",O_RDWR | O_NONBLOCK | O_SYNC);

    if (fd < 0) { perror("error"); return EXIT_FAILURE; }

    fcntl( fd, F_SETFL, O_NONBLOCK );

    newtio.c_cflag =  CLOCAL | CREAD;

    newtio.c_iflag = IGNPAR | ICRNL;
    newtio.c_oflag = 0;

    newtio.c_lflag = ICANON;
    newtio.c_cc[VMIN] = 0;

    newtio.c_cc[VTIME] = 10;

    tcflush(fd, TCIFLUSH);

    tcsetattr( fd, TCSANOW, &newtio );

        sen = write( fd, buf, sizeof(buf) );


        printf("No. of bytes written  = %d\n", sen);

        tcsetattr(fd, TCSAFLUSH, &newtio);

        total =ioctl(fd, FIONREAD, &bytes);

        printf("No. of bytes in the input buffer = %d\n", total);


  return 0;

}

Any help will be highly appreciated.

Thanks,
Nick

[Rubberman]

Buffering is one thing. Reading is another. The only way you could do that would be to have a cable that connects the serial port back to itself.