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

static inline void ccnt_start(void)
{
    __asm__ volatile ("mcr p15, 0,   %0,  c9,  c12, 1" :: "r"(1<<31));
}

static inline void ccnt_stop(void)
{
    __asm__ volatile ("mcr p15, 0,   %0,  c9,  c12, 2" :: "r"(1<<31));
    __asm__ volatile ("mcr p15, 0,   %0,  c9,  c12, 0" :: "r"(0));
}

static inline unsigned ccnt_read(void)
{
    unsigned cc;
    __asm__ volatile ("mrc p15, 0,   %0,  c9,  c13, 0" : "=r"(cc));
    return cc;
}

static inline void ccnt_init(void)
{
    ccnt_stop();
    __asm__ volatile ("mcr p15, 0,   %0,  c9,  c12, 0" :: "r"(5));
}

static unsigned
tv_diff(struct timeval *tv1, struct timeval *tv2)
{
    return (tv2->tv_sec - tv1->tv_sec) * 1000000 +
        (tv2->tv_usec - tv1->tv_usec);
}

int main(int argc, char **argv)
{
    struct timeval tv1, tv2;
    unsigned cc1, cc2, us;
    int spin;

    if (argc > 1) {
        if (!strcmp(argv[1], "1") || !strcmp(argv[1], "on")) {
            ccnt_init();
            ccnt_start();
        } else if (!strcmp(argv[1], "0") || !strcmp(argv[1], "off")) {
            ccnt_stop();
        } else {
            fprintf(stderr, "usage: %s [on|off]\n", argv[0]);
            return 1;
        }
        return 0;
    }

    ccnt_init();
    ccnt_start();
    cc1 = ccnt_read();
    gettimeofday(&tv1, NULL);
    spin = 1<<30;
    while (spin--) __asm__ volatile ("");
    cc2 = ccnt_read();
    gettimeofday(&tv2, NULL);

    cc2 -= cc1;
    us = tv_diff(&tv1, &tv2);
    printf("%10u cycles in %7u us, %7.2f MHz\n", cc2, us, (float)cc2 / us);

#if 0
    cc1 = ccnt_read();
    for (int i = 0; i < 100; i++)
        gettimeofday(&tv1, NULL);
    cc2 = ccnt_read();
    printf("%u cycles in gettimeofday()\n", (cc2 - cc1) / 100);
#endif

    ccnt_stop();

    return 0;
}