Programming

read: Interrupted system call

    /* 
     * Signal handling 
     */ 
    struct sigaction act;
    /* define the signal action */
    act.sa_handler = terminate;
    /* make "act" an empty signal set */
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;
    /* instead of SIGHUP do "act" */
    sigaction(SIGHUP, &act, 0);
    
    /* 
     * main loop : runs until the signal handler  
     * receives a SIGINT to change "keep_running" to 0
     */
    while(keep_running){
        /* wait for irq */
        retval = await_rtc_irq(freq);
        /*.....*/
    }
    syslog (LOG_NOTICE, "clean up and exit\n");
    close(fdlock);
    unlink(DAQD_LOCK_FILE);
    closelog();
    return 0;

long int await_rtc_irq(int freq)
{
    int fd;
    long int retval, controlval;
    unsigned long data;
    
    /* open the RTC IRQ */
    fd = open ("/dev/rtc", O_RDONLY);
    
    if (freq == 1) {
        /* Enable periodic 1Hz interrupts */
        retval = ioctl(fd, RTC_UIE_ON, 0);
        if (retval == -1) {
            perror("ioctl");
            exit(errno);
        }
        /* call the read function to await the Alarm interrupt */
        retval = read(fd, &data, sizeof(unsigned long));
        if (retval == -1) {
            perror("read");
            exit(errno);
        }
        controlval = retval;
        /* Turn off update interrupts */
        retval = ioctl(fd, RTC_UIE_OFF, 0);
        if (retval == -1) {
            perror("RTC_UIE_OFF ioctl");
            exit(errno);
        }    
    }
    /* For frequencies different from 1 the irq has to be set differently.*/
    else if (freq == 2 || freq == 4 || freq == 8 || freq == 16 || 
         freq == 32 ||   freq == 64|| freq ==128){
        /* set peridoc interrupt frequncy */
        retval = ioctl(fd, RTC_IRQP_SET, freq);
        if (retval == -1) {
            perror("ioctl");
            exit(errno);
        }
        /* Enable periodic interrupts */
        retval = ioctl(fd, RTC_PIE_ON, 0);
        if (retval == -1) {
            perror("ioctl");
            exit(errno);
        }
        /* call the read function to await the Alarm interrupt */
        retval = read(fd, &data, sizeof(unsigned long));
        if (retval == -1) {
            perror("read");
            exit(errno);
        }
        controlval = retval;
        /* Disable periodic interrupts */
        retval = ioctl(fd, RTC_PIE_OFF, 0);
        if (retval == -1) {
            perror("RTC_PIE_OFF ioctl");
            exit(errno);
        }
    }
    else {
        puts("frequency not supported");
        exit(1);
    }
    close(fd);
    return(controlval);
}