#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <getopt.h>
#include <sched.h>
#include <unistd.h>

#define rdtsc(low,high) \
     __asm__ __volatile__("rdtsc" : "=a" (low), "=d" (high))

#define rdtscl(low) \
     __asm__ __volatile__("rdtsc" : "=a" (low) : : "edx")

#define rdtscll(val) \
     __asm__ __volatile__("rdtsc" : "=A" (val))

#define LOOPS 100.0

int main(int argc, char **argv)
{
	int c;
	unsigned long long start, end, tps = 0;
	double cal;
	double max=0,min=0,avg=0;
	int i;
	pid_t pid;
	struct sched_param sp;
	double sleeptime;
	unsigned long sec,nsec;

	sleeptime = 0.01;
	sec = sleeptime;
	nsec = (sleeptime-sec) * 1000000000;
	
	pid = getpid();

	memset(&sp,0,sizeof(sp));
	sp.sched_priority = sched_get_priority_max(SCHED_FIFO);
	sched_setscheduler(pid,SCHED_FIFO,&sp);

	while ((c=getopt(argc,argv,"c:")) != -1) {
		switch (c) {
			case 'c':
				tps = strtoll(optarg,NULL,10);
				break;
			default:
				exit(0);
		}
	}

	if (!tps) {
		printf("starting calibrate\n");
		rdtscll(start);
		sleep(8);
		rdtscll(end);

		tps = end - start;
		tps >>= 3;
		printf("finished calibrate: ");
	} else {
		printf("passed in calibrate: ");
	}
	cal = tps;
	cal /= 1000000.0;

	printf("%.4fMHz %llu\n",cal,tps);

	for (i=0; i < LOOPS; i++) {
		struct timespec req = { sec, nsec };
		unsigned long long t;
		rdtscll(start);
		nanosleep(&req,NULL);
		rdtscll(end);
		t = end - start;
		cal = t;
		cal /= (double)tps;
		if (!i || cal > max)
			max = cal;
		if (!i || cal < min)
			min = cal;
		avg += cal;
	}

	avg /= LOOPS;
	
	printf("time slept: %.9f sec: %lu nsec: %lu\n",sleeptime,sec,nsec);
	printf("max: %.9f\n",max);
	printf("min: %.9f\n",min);
	printf("avg: %.9f\n",avg);

	printf("greatest time over: %.3f usecs\n",(max-sleeptime)*1000000.0);
	if (min > sleeptime) {
		printf("never ran under (good!)\n");
	} else {
		printf("Ran under!!! (by %.9f) nsecs\n",sleeptime-min);
	}

	if (avg > sleeptime)
		printf("average time over: %.3f usecs\n",(avg-sleeptime)*1000000.0);
	else
		printf("average time ran under???\n");
	
	exit(0);
}