test_time.c

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/**
 * @file test_time.c
 * Tests clocks/timekeeping.
 */

#include <px4_platform_common/px4_config.h>
#include <px4_platform_common/defines.h>
#include <px4_platform_common/posix.h>
#include <sys/types.h>

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

#include "tests_main.h"

#include <math.h>
#include <float.h>
#include <drivers/drv_hrt.h>


static hrt_abstime
cycletime(void)
{
	/* emulate hrt_absolute_time using the cycle counter */
	static uint64_t basetime;
	static uint32_t lasttime;
	uint32_t cycles;

	cycles = *(unsigned long *)0xe0001004;

	if (cycles < lasttime) {
		basetime += 0x100000000ULL;
	}

	lasttime = cycles;

	return (basetime + cycles) / 168;	/* XXX magic number */
}

int test_time(int argc, char *argv[])
{
	int maxdelta = 0;

	/* enable the cycle counter */
	(*(unsigned long *)0xe000edfc) |= (1 << 24);    /* DEMCR |= DEMCR_TRCENA */
	(*(unsigned long *)0xe0001000) |= 1;    	/* DWT_CTRL |= DWT_CYCCNT_ENA */

	/* get an average delta between the two clocks - this should stay roughly the same */
	int delta = 0;

	for (unsigned i = 0; i < 100; i++) {
		irqstate_t flags = px4_enter_critical_section();
		hrt_abstime h = hrt_absolute_time();
		hrt_abstime c = cycletime();
		px4_leave_critical_section(flags);

		delta += h - c;
	}

	int lowdelta = abs(delta / 100);

	/* loop checking the time */
	for (unsigned i = 0; i < 100; i++) {

		usleep(rand() % SHRT_MAX);

		uint32_t flags = px4_enter_critical_section();

		hrt_abstime c = cycletime();
		hrt_abstime h = hrt_absolute_time();

		px4_leave_critical_section(flags);

		delta = h - c;
		int deltadelta = abs(delta - lowdelta);

		if (deltadelta > maxdelta) {
			maxdelta = deltadelta;
		}

		if (deltadelta > 1000) {
			fprintf(stderr, "h %" PRIu64 " c %" PRIu64 " d %d\n", h, c, delta - lowdelta);
		}
	}

	printf("Maximum jitter %dus\n", maxdelta);

	return 0;
}