Catch BREAK signal on UART bus.

[marius.m...@gmail.com]

Hello,

I'm have connected some device on one of the UART peripherals of the BeagleBone Black, and now I would like to be able to somehow detect if there's a "BREAK" sequence present (with some kind of Linux signaling method).

I have tried with this code:

#include <errno.h>
#include <fcntl.h>
#include <string.h>
#include <termios.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>


#define error_message printf


int set_interface_attribs (int fd, int speed, int parity) {
        struct termios tty;

        memset (&tty, 0, sizeof tty);

        if (tcgetattr (fd, &tty) != 0) {
                error_message ("error %d from tcgetattr", errno);
                return -1;
        }


        cfsetospeed (&tty, speed);
        cfsetispeed (&tty, speed);


        tty.c_cflag = (tty.c_cflag & ~CSIZE) | CS8;     // 8-bit chars
        tty.c_iflag &= IGNBRK;         // disable break processing
        tty.c_lflag = 0;                // no signaling chars, no echo,
                                        // no canonical processing
        tty.c_oflag = 0;                // no remapping, no delays
        tty.c_cc[VMIN]  = 0;            // read doesn't block
        tty.c_cc[VTIME] = 5;            // 0.5 seconds read timeout


        tty.c_iflag &= ~(IXON | IXOFF | IXANY); // shut off xon/xoff ctrl


        tty.c_cflag |= (CLOCAL | CREAD);// ignore modem controls,
                                        // enable reading
        tty.c_cflag &= ~(PARENB | PARODD);      // shut off parity
        tty.c_cflag |= parity;
        tty.c_cflag &= ~CSTOPB;
        tty.c_cflag &= ~CRTSCTS;
        //tty.c_iflag = ~BRKINT | ~INPCK;


        if (tcsetattr (fd, TCSANOW, &tty) != 0) {
                error_message ("error %d from tcsetattr", errno);
                return -1;
        }
        return 0;
}

void breakHandler(int signo) {
    printf("\n\nCATCHED!!!\n\n");
}


int main() {


 char *portname = "/dev/ttyO5";


 int fd = open (portname, O_NOCTTY);

 if (fd < 0) {
     error_message ("error %d opening %s: %s", errno, portname, strerror (errno));
     return;
 }


 set_interface_attribs (fd, B19200, 0);  // set speed to 192,000 bps, 8n1 (no parity)

 char buf [100];


 if (signal(SIGINT, breakHandler) == SIG_ERR) {
     printf("\n\nCan't catch SIGINT!\n\n");
 }


 fcntl(fd, F_SETOWN, getpid());


 struct sigaction saio; /* definition of signal action */

 saio.sa_handler = breakHandler;
 saio.sa_flags = 0;
 saio.sa_restorer = NULL;

 sigaction(SIGINT, &saio, NULL);


 while(1) {
     int n = read (fd, buf, sizeof buf);  // read up to 100 characters if ready to read
     usleep ((95 + 25) * 100);
     printf("\n I read:\n");


     int i;

     for(i = 0; i < n; i++) {
         printf("%#08x ", buf[i]);
     }


     printf("\nError: %s\n", strerror(errno));
 }

 return 0;
}

But it seems that it's not working, the signal is only triggered when I press CTRL+C on my keyboard.

What should be the problem?

Thanks.

[William Hermans]

Are you running this code as root, or a regular user ?

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[marius.m...@gmail.com]

as root