serial port programming question !!!!!!!!!!!!!!Help required

["srinuk" <srinuk@sasken.com>]

Ken stone,

 

I am an engineer working with motorola.I am doing a project and I have a question on Red hat linux 7.1.

 

Description of problem:

 

I have two PC's connected using serial cable (RS232 NULL modem).On one of the PC's I have DOS based serial communication software running(written

by polling method and not by interrupt mechanism).On the other computer I have linux serial communication program running.

The PC with dos based serial communication is sending the packets (I have verified this by shorting the Tx and Rx pins on the 9 pin comport)

But the PC with linux based serial communication software is not receiving the packets.I feel the problem with PC with linux.

It is not receiving the packets.I have pasted the program here as under(this is I have taken from HOWTO document of linux).

 

Can you please give pointers as to what we can check so that our serial communication from DOS to linux is successful.

 

Will be grateful for your help in this regard.

 

#include <termios.h>
      #include <stdio.h>
      #include <unistd.h>
      #include <fcntl.h>
      #include <sys/signal.h>
      #include <sys/types.h>

 

      #define BAUDRATE B38400
      #define MODEMDEVICE "/dev/ttyS1"
      #define _POSIX_SOURCE 1 /* POSIX compliant source */
      #define FALSE 0
      #define TRUE 1

 

      volatile int STOP=FALSE;

 

      void signal_handler_IO (int status);   /* definition of signal handler
*/
      int wait_flag=TRUE;                    /* TRUE while no signal
received */

 

      main()
      {
        int fd,c, res;
        struct termios oldtio,newtio;
        struct sigaction saio;           /* definition of signal action */
        char buf[255];

 

        /* open the device to be non-blocking (read will return immediatly) */
        fd = open(MODEMDEVICE, O_RDWR | O_NOCTTY | O_NONBLOCK);
        if (fd <0) {perror(MODEMDEVICE); exit(-1); }

 

        /* install the signal handler before making the device asynchronous */
        saio.sa_handler = signal_handler_IO;
        saio.sa_mask = 0;
        saio.sa_flags = 0;
        saio.sa_restorer = NULL;
        sigaction(SIGIO,&saio,NULL);

 

        /* allow the process to receive SIGIO */
        fcntl(fd, F_SETOWN, getpid());
        /* Make the file descriptor asynchronous (the manual page says only
           O_APPEND and O_NONBLOCK, will work with F_SETFL...) */
        fcntl(fd, F_SETFL, FASYNC);

 

        tcgetattr(fd,&oldtio); /* save current port settings */
        /* set new port settings for canonical input processing */
        newtio.c_cflag = BAUDRATE | CRTSCTS | CS8 | CLOCAL | CREAD;
        newtio.c_iflag = IGNPAR | ICRNL;
        newtio.c_oflag = 0;
        newtio.c_lflag = ICANON;
        newtio.c_cc[VMIN]=1;
        newtio.c_cc[VTIME]=0;
        tcflush(fd, TCIFLUSH);
        tcsetattr(fd,TCSANOW,&newtio);

 

        /* loop while waiting for input. normally we would do something
           useful here */
        while (STOP==FALSE) {
          printf(".\n");usleep(100000);
          /* after receiving SIGIO, wait_flag = FALSE, input is available
             and can be read */
          if (wait_flag==FALSE) {
            res = read(fd,buf,255);
            buf[res]=0;
            printf(":%s:%d\n", buf, res);
            if (res==1) STOP=TRUE; /* stop loop if only a CR was input */
            wait_flag = TRUE;      /* wait for new input */
          }
        }
        /* restore old port settings */
        tcsetattr(fd,TCSANOW,&oldtio);
      }

 

/***************************************************************************
      * signal handler. sets wait_flag to FALSE, to indicate above loop that
*
      * characters have been received.
*

 

***************************************************************************/

 

      void signal_handler_IO (int status)
      {
        printf("received SIGIO signal.\n");
        wait_flag = FALSE;
      }

 

 

Best Regards,

Srinivas

 

 

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