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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.
*
* This version returns the number of nanoseconds since Timer_initialize()
* exited, since the '604 is very fast at 300MHz. Actual resolution is
* 60 nsec.
*
* 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.OARcorp.com/rtems/license.html.
*
* $Id$
*/
#include <rtems.h>
#include <bsp.h>
rtems_unsigned32 Timer_start;
rtems_boolean Timer_driver_Find_average_overhead;
void Timer_initialize( void )
{
rtems_unsigned32 clicks;
asm volatile ("mfspr %0,268" : "=r" (clicks) :);
Timer_start = clicks;
}
/*
* 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 7 /* On average, it takes 7.4 nanoseconds */
/* (Y countdowns) to start/stop the timer. */
#define NSEC_PER_TICK 60
int Read_timer( void )
{
rtems_unsigned32 clicks;
rtems_unsigned32 total;
/*
* Read the timer and see how many clicks it has been since we started.
* Timer overflows every 257 seconds, so multiple overflows are deemed
* impossible.
*/
asm volatile ("mfspr %0,268" : "=r" (clicks) :);
total = (clicks - Timer_start);
if ( Timer_driver_Find_average_overhead == 1 ) {
return total * NSEC_PER_TICK; /* in nanoseconds */
} else {
/*
* convert total into nanoseconds
*/
return total * NSEC_PER_TICK - 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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