timer.c

RTEMS (Real-Time Executive for Multiprocessor Systems) is a free open source real-time operating sys

/*  timer.c
 *
 *  This file manages the benchmark timer used by the RTEMS Timing Test
 *  Suite.  Each measured time period is demarcated by calls to
 *  Timer_initialize() and Read_timer().  Read_timer() usually returns
 *  the number of microseconds since 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).
 *
 *  $Id: timer.c,v 1.5.6.1 2003/09/04 17:32:05 joel Exp $
 */

#ifndef lint
static char _sccsid[] = "@(#)timer.c 05/07/96     1.4\n";
#endif

#include <rtems.h>

#define CLOCKS_PER_MICROSECOND ( CPU_CLOCK_RATE_MHZ )
#define TIMER_MAX_VALUE 0xffffffff

static unsigned32 read_timer( void )
{
  return 0; /* do something with real hardware here */
}

static rtems_boolean Timer_driver_Find_average_overhead;
static unsigned32 Timer_initial_value = 0;

void Timer_initialize( void )
{
   Timer_initial_value = read_timer();

  /*
   *  Somehow start the timer
   */

  /* Timer is always running */
}

/*
 *  The following controls the behavior of Read_timer().
 *
 *  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      8  /* It typically takes X.X microseconds */
                             /* (Y countdowns) to start/stop the timer. */
                             /* This value is in cycles. */
#define LEAST_VALID       1  /* Don't trust a clicks value lower than this */

int Read_timer( void )
{
  unsigned64 clicks;
  unsigned32 total;

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

  clicks = read_timer();   /* XXX: read some HW here */
  if (clicks < Timer_initial_value)
  {
      clicks += TIMER_MAX_VALUE;
  }
  clicks -= Timer_initial_value;

  /*
   *  Total is calculated by taking into account the number of timer overflow
   *  interrupts since the timer was initialized and clicks since the last
   *  interrupts.
   */
#if 0 /* leave total in number of cycles */
   total = clicks / CLOCKS_PER_MICROSECOND;
#else
   total = clicks;
#endif

  if ( Timer_driver_Find_average_overhead == 1 )
    return total;          /* in # cycles units */
  else {
    if ( total < LEAST_VALID )
      return 0;            /* below timer resolution */
  /*
   *  leave total in cycles
   */
      return (total - AVG_OVERHEAD);
    }
}

/*
 *  Empty function call used in loops to measure basic cost of looping
 *  in Timing Test Suite.
 */

rtems_status_code Empty_function( void )
{
  return RTEMS_SUCCESSFUL;
}

void Set_find_average_overhead(
  rtems_boolean find_flag
)
{
  Timer_driver_Find_average_overhead = find_flag;
}