Realization and application of real time timer in C language under Linux

Linux also has a high-precision timer, that is posix_timer. I remember looking at the code when the Clock_realtime timer seems to use the RDTSC instructions, but now not sure, first put aside. In principle, you can use the RDTSC instruction in the frequency conversion, because the frequency of the CPU is also known to us, the kernel is also known when the frequency conversion.

Here is my timer_create example, compile with RT library, this is the Linux Realtime Library:

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;
}

Output results:

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