signal & setitimer() 에 대한 질문입니다.

signal 과 setitimer함수에 관한 프로그램인데...
어렵네요....정말......
그리구 아래서 interval.tv_sec 가 10이 되더군요...
interval.tv_usec은 0이 되구요...왜 이렇게 되는거지요?
제발 :( 좀 알려주세요~~~~

#include <sys/time.h>
#include <signal.h>
#include <unistd.h>
#include <stdio.h>

long unsigned int fibonacci(unsigned int n);
void sig_handler(int signo);
long elapsed_usecs(long a, long b);

static long p_realt_secs = 0;
static struct itimerval p_realt;

main(/*int argc, char argv[]*/)
{
        long unsigned fib = 0;
        unsigned int fibarg;

        fibarg = 40;

        p_realt.it_interval.tv_sec = 9;
        p_realt.it_interval.tv_usec = 999999;
        p_realt.it_value.tv_sec = 9;
        p_realt.it_value.tv_usec = 999999;

        if(signal(SIGALRM, sig_handler) == SIG_ERR)
                printf("Unable to create signal handler for SIGALRM");

        if(setitimer(ITIMER_REAL, &p_realt, NULL) == -1)
                perror("parent real timer set error");

        fib = fibonacci(fibarg);
        fib = fibonacci(fibarg);

        getitimer(ITIMER_REAL, &p_realt);

        printf("parent fib = %ld, real time = %ld sec, %ld %ld msec\n", fib, p_realt.it_value.tv_sec,p_realt.it_value.tv_usec,
                        elapsed_usecs(p_realt.it_value.tv_sec, p_realt.it_value.tv_usec)/1000);
        printf("\n\n%ld   %ld\n\n",p_realt.it_interval.tv_sec, p_realt.it_interval.tv_usec);
}

long unsigned int fibonacci(unsigned int n)
{
        if(n==0)
                return 0;
        else if(n==1 || n==2)
                return 1;
        else
                return(fibonacci(n-1) + fibonacci(n-2));
}

void sig_handler(int signo)
{
        if(signo == SIGALRM)
                printf("Signal is receive");
}


long elapsed_usecs(long a, long b)
{
        return (a*1000000 + b);
}