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/*
* Copyright (c) 2014, 2017 embedded brains GmbH. All rights reserved.
*
* embedded brains GmbH
* Dornierstr. 4
* 82178 Puchheim
* Germany
* <rtems@embedded-brains.de>
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
* http://www.rtems.org/license/LICENSE.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <rtems/test.h>
#include <rtems.h>
static uint_fast32_t estimate_busy_loop_maximum( void )
{
uint_fast32_t units = 0;
uint_fast32_t initial = rtems_clock_get_ticks_since_boot();
while ( initial == rtems_clock_get_ticks_since_boot() ) {
++units;
}
return units;
}
static uint_fast32_t wait_for_tick_change( void )
{
uint_fast32_t initial = rtems_clock_get_ticks_since_boot();
uint_fast32_t now;
do {
now = rtems_clock_get_ticks_since_boot();
} while ( now == initial );
return now;
}
/*
* It is important that we use actually use the same rtems_test_busy() function
* at the various places, since otherwise the obtained maximum value might be
* wrong. So, the compiler must not inline this function.
*/
RTEMS_NO_INLINE void rtems_test_busy( uint_fast32_t count )
{
uint_fast32_t i = 0;
do {
__asm__ volatile ("");
++i;
} while ( i < count );
}
uint_fast32_t rtems_test_get_one_tick_busy_count( 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 */
wait_for_tick_change();
b = 2 * estimate_busy_loop_maximum();
while ( true ) {
last = wait_for_tick_change();
rtems_test_busy( b );
now = rtems_clock_get_ticks_since_boot();
if ( now != last ) {
break;
}
b *= 2;
last = now;
}
/* Find a good value */
do {
m = ( a + b ) / 2;
last = wait_for_tick_change();
rtems_test_busy( m );
now = rtems_clock_get_ticks_since_boot();
if ( now != last ) {
b = m;
} else {
a = m;
}
} while ( b - a > 1 );
return m;
}
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