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/* 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).
* All rights assigned to U.S. Government, 1994.
*
* This material may be reproduced by or for the U.S. Government pursuant
* to the copyright license under the clause at DFARS 252.227-7013. This
* notice must appear in all copies of this file and its derivatives.
*
* timer.c,v 1.2 1995/05/31 16:56:39 joel Exp
*/
#ifndef lint
static char _sccsid[] = "@(#)timer.c 05/07/96 1.4\n";
#endif
#include <rtems.h>
#include <bsp.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 on 4650 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;
}
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