t-test-busy-tick.c

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/* SPDX-License-Identifier: BSD-2-Clause */

/*
 * Copyright (C) 2014, 2020 embedded brains GmbH (http://www.embedded-brains.de)
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include <rtems/test.h>

#include <rtems.h>

static uint_fast32_t
T_estimate_busy_loop_maximum(void)
{
    uint_fast32_t initial;
    uint_fast32_t units;

    initial = rtems_clock_get_ticks_since_boot();
    units = 0;

    while (initial == rtems_clock_get_ticks_since_boot()) {
        ++units;
    }

    return units;
}

static uint_fast32_t
T_wait_for_tick_change(void)
{
    uint_fast32_t initial;
    uint_fast32_t now;

    initial = rtems_clock_get_ticks_since_boot();

    do {
        now = rtems_clock_get_ticks_since_boot();
    } while (now == initial);

    return now;
}

uint_fast32_t
T_get_one_clock_tick_busy(void)
{
    uint_fast32_t last;
    uint_fast32_t now;
    uint_fast32_t a;
    uint_fast32_t b;
    uint_fast32_t m;

    /* Choose a lower bound */
    a = 1;

    /* Estimate an upper bound */

    T_wait_for_tick_change();
    b = 2 * T_estimate_busy_loop_maximum();

    while (true) {
        last = T_wait_for_tick_change();
        T_busy(b);
        now = rtems_clock_get_ticks_since_boot();

        if (now != last) {
            break;
        }

        b *= 2;
    }

    /* Find a good value */
    do {
        m = (a + b) / 2;

        last = T_wait_for_tick_change();
        T_busy(m);
        now = rtems_clock_get_ticks_since_boot();

        if (now != last) {
            b = m;
        } else {
            a = m;
        }
    } while (b - a > 1);

    return m;
}