linux下还有一种高精度的定时器，那就是posix_timer.我记得以前看代码的时候CLOCK_REALTIME的定时器似乎用的就是rdtsc指令，不过现在不确定了，先放到一边。原理上来说，可以在变频的时候也使用rdtsc指令，因为CPU的频率我们也是知道的，变频的时候内核也是知道的。
下面是我的timer_create的例子，编译的时候要加上rt库，这是linux的realtime库：
gcc -o test test.c
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <stdlib.h>
#include <time.h>
#define rdtsc(low,high) __asm__ __volatile__("rdtsc" : "=a" (low), "=d" (high))
timer_t tt;
void handler (int sig, siginfo_t * extra, void *cruft)
{
static last_i=0;
unsigned int i, j;
rdtsc(i,j);
printf ("time:%u, %u, [%u] %uHZ ", j, i, i-last_i, (i-last_i)*10/1000000);
last_i = i;
}
int main ()
{
int i=0;
sigset_t sigset;
sigfillset (&sigset);
sigdelset (&sigset, SIGRTMIN);
sigprocmask (SIG_SETMASK, &sigset, NULL);
struct sigaction sa;
sigfillset (&sa.sa_mask);
sa.sa_flags = SA_SIGINFO;
sa.sa_sigaction = handler;
if (sigaction (SIGRTMIN, &sa, NULL) < 0)
{
perror ("sigaction failed ");
exit (-1);
}
struct sigevent timer_event;
struct itimerspec timer;
timer.it_interval.tv_sec = 0;
timer.it_interval.tv_nsec = 100 * 1000 * 1000;
timer.it_value = timer.it_interval;
timer_event.sigev_notify = SIGEV_SIGNAL;
timer_event.sigev_signo = SIGRTMIN;
timer_event.sigev_value.sival_ptr = (void *) &tt;
if (timer_create (CLOCK_REALTIME, &timer_event, &tt) < 0)
{
perror ("timer_create failed");
exit (-1);
}
if (timer_settime (tt, 0, &timer, NULL) < 0)
{
perror ("timer_settime failed");
exit (-1);
}
while (i++ < 10)
{
pause ();
}
return 0;
}
输出结果：
time:166081, 1934350847, [1934350847] 2163HZ
time:166081, 2120528291, [186177444] 1861HZ
time:166081, 2306679576, [186151285] 1861HZ
time:166081, 2494695630, [188016054] 1880HZ
time:166081, 2680865389, [186169759] 1861HZ
time:166081, 2867018473, [186153084] 1861HZ
time:166081, 3053152230, [186133757] 1861HZ
time:166081, 3239309935, [186157705] 1861HZ
time:166081, 3425467261, [186157326] 1861HZ
time:166081, 3611639266, [186172005] 1861HZ