source: rtems/c/src/lib/libcpu/powerpc/mpc505/timer/timer.c @ 9b4422a2

/*  timer.c
 *
 *  This file manages the benchmark timer used by the RTEMS Timing Test
 *  Suite.  Each measured time period is demarcated by calls to
 *  benchmark_timer_initialize() and benchmark_timer_read().  benchmark_timer_read() usually returns
 *  the number of microseconds since benchmark_timer_initialize() exitted.
 *
 *  NOTE: It is important that the timer start/stop overhead be
 *        determined when porting or modifying this code.
 *
 *  COPYRIGHT (c) 1989, 1990, 1991, 1992, 1993, 1994.
 *  On-Line Applications Research Corporation (OAR).
 */

#include <rtems.h>

bool benchmark_timer_find_average_overhead;

static unsigned int volatile lastInitValue;

void benchmark_timer_initialize( void )
{
  __asm__ volatile( " mftb %0": "=r" (lastInitValue) );
}

/*
 *  The following controls the behavior of benchmark_timer_read().
 *
 *  AVG_OVEREHAD is the overhead for starting and stopping the timer.  It
 *  is usually deducted from the number returned.
 *
 *  LEAST_VALID is the lowest number this routine should trust.  Numbers
 *  below this are "noise" and zero is returned.
 */

#define AVG_OVERHEAD      0  /* It typically takes X.X microseconds */
                             /* (Y countdowns) to start/stop the timer. */
                             /* This value is in microseconds. */
#define LEAST_VALID       1  /* Don't trust a clicks value lower than this */

int benchmark_timer_read( void )
{
  uint32_t   value;
  __asm__ volatile ( " mftb %0": "=r" (value) );
  return value - lastInitValue;
}

void benchmark_timer_disable_subtracting_average_overhead(bool find_flag)
{
  benchmark_timer_find_average_overhead = find_flag;
}