spence@panix.com (Michael D. Spence) writes:
> Windows has QueryPerformanceFrequency and QueryPerformanceCounter, 
> which evidently do something with a high-resolution clock.  
> 
> Does NetBSD offer access to this device?

Modern x86 have a cpu clock cycle counter.  If you are running with a
constant clock you can use the TSC counter. (This obviously doesn't
work if you have one of those goofy "speed step" portables that turn
the clock speed up and down at run-time).

-wolfgang


/* cc -O2 -g -Wall -Wmissing-prototypes -Wmissing-declarations -Wuninitialized tsc2.c -o tsc2 */

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

typedef unsigned long long u64;
double          timestamp(void);
inline          u64 getTick64(void);

inline          u64
getTick64(void)
{
    u64             ticks;
    asm             volatile("rdtsc":"=A"(ticks));
    return ticks;
}

double
timestamp(void)
{
    double          sec;
    struct timeval  ts;

    gettimeofday(&ts, NULL);
    sec = ts.tv_sec;
    sec += ts.tv_usec * 1e-6;

    return (sec);
}

int
main(void)
{
    int             i;
    u64             start = 0,
                    end;
    double          fstart = 0.0,
                    fend,
                    ticspersec;

    fstart = timestamp();
    start = getTick64();
    sleep(1);
    fend = timestamp();
    end = getTick64();
    ticspersec = (end - start) / (fend - fstart);

    for (i = 0; i < 10000000; i++) {
	start = getTick64();
	fstart = timestamp();
	fend = timestamp();
	end = getTick64();

	if (fend < fstart) {
	    printf("retrograde: %1.20e -> %1.20e (%1.20e)\n",
		   fstart, fend, fend - fstart);
	    printf(" tsc: %llu -> %llu (%llu tics, %1.20e seconds)\n",
		   start, end, end - start, (end - start) / ticspersec);
	    printf("error ~= %1.20e\n",
		   fend - fstart - ((end - start) / ticspersec));
	}
    }
    exit(0);
}



-- 
Wolfgang S. Rupprecht 		     http://www.wsrcc.com/wolfgang/
(NOTE: The email address above is valid.  Edit it at your own peril.)