path: root/c/src/lib/libbsp/no_cpu/no_bsp/timer/timer.c

/*  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) 1989-1999.
 *  On-Line Applications Research Corporation (OAR).
 *
 *  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.
 */

#include <rtems.h>
#include <rtems/btimer.h>
#include <bsp.h>

uint32_t         Timer_interrupts;
bool benchmark_timer_find_average_overhead;

void benchmark_timer_initialize( void )
{

  /*
   *  Timer has never overflowed.  This may not be necessary on some
   *  implemenations of timer but ....
   */

  Timer_interrupts = 0;

  /*
   *  Somehow start the timer
   */
}

/*
 *  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 */

uint32_t benchmark_timer_read( void )
{
  uint32_t         clicks;
  uint32_t         total;

  /*
   *  Read the timer and see how many clicks it has been since we started.
   */

  clicks = 0;   /* XXX: read some HW here */

  /*
   *  Total is calculated by taking into account the number of timer overflow
   *  interrupts since the timer was initialized and clicks since the last
   *  interrupts.
   */

  total = clicks * 0;

  if ( benchmark_timer_find_average_overhead == true )
    return total;          /* in XXX microsecond units */
  else {
    if ( total < LEAST_VALID )
      return 0;            /* below timer resolution */
  /*
   *  Somehow convert total into microseconds
   */
      return (total - AVG_OVERHEAD);
    }
}

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