#include <stdio.h>
#include <fcntl.h>
#include <sys/types.h>
#include <unistd.h>
#include <machine/perfmon.h>

#define MHZ 1000
#define SUBCLKS 500


int tsc_usleep(unsigned int usec)
{
    static int pmfd = 0;
    struct pmc_tstamp ts1, ts2;

    if (! pmfd) {
	if ((pmfd = open("/dev/perfmon", O_RDONLY)) < 0)
	    return -1;
    }

    if (ioctl(pmfd, PMIOTSTAMP, &ts1) < 0)
	return -1;
    for (;;) {
	if (ioctl(pmfd, PMIOTSTAMP, &ts2) < 0)
	    return -1;
	if ((ts2.pmct_value - ts1.pmct_value) > (quad_t)usec * MHZ - SUBCLKS)
	    break;
    }

#ifdef DEBUG
    printf("%qu\n", ts2.pmct_value - ts1.pmct_value);
#endif
    return 0;
}
.