#include <stdio.h>
#include <signal.h>

void timer(int sig)
{
    if(SIGALRM == sig)
    {
        printf("timer\n");
        alarm(1);    //we contimue set the timer
    }

    return ;
}

int main()
{
    signal(SIGALRM, timer); //relate the signal and function

    alarm(1);    //trigger the timer

    getchar();

    return 0;
}

#include <stdio.h>
#include <linux/rtc.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <stdlib.h>

int main(int argc, char* argv[])
{
    unsigned long i = 0;
    unsigned long data = 0;
    int retval = 0;
    int fd = open ("/dev/rtc", O_RDONLY);

    if(fd < 0)
    {
        perror("open");
        exit(errno);
    }

    /*Set the freq as 4Hz*/
    if(ioctl(fd, RTC_IRQP_SET, 1) < 0)
    {
        perror("ioctl(RTC_IRQP_SET)");
        close(fd);
        exit(errno);
    }
    /* Enable periodic interrupts */
    if(ioctl(fd, RTC_PIE_ON, 0) < 0)
    {
        perror("ioctl(RTC_PIE_ON)");
        close(fd);
        exit(errno);
    }

    for(i = 0; i < 100; i++)
    {
        if(read(fd, &data, sizeof(unsigned long)) < 0)
        {
            perror("read");
            close(fd);
            exit(errno);

        }
        printf("timer\n");
    }
    /* Disable periodic interrupts */
    ioctl(fd, RTC_PIE_OFF, 0);
    close(fd);

    return 0;
}

#include <sys/time.h>
#include <sys/select.h>
#include <time.h>
#include <stdio.h>

/*seconds: the seconds; mseconds: the micro seconds*/
void setTimer(int seconds, int mseconds)
{
    struct timeval temp;

    temp.tv_sec = seconds;
    temp.tv_usec = mseconds;

    select(0, NULL, NULL, NULL, &temp);
    printf("timer\n");

    return ;
}

int main()
{
    int i;

    for(i = 0 ; i < 100; i++)
        setTimer(1, 0);

    return 0;
}