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/*
* Cogent CSB337 Timer driver
*
* This uses timer 0 for timing measurments.
*
* Copyright (c) 2004 by Jay Monkman <jtm@lopingdog.com>
*
* The license and distribution terms for this file may be
* found in the file LICENSE in this distribution or at
*
* http://www.rtems.com/license/LICENSE.
*
* Notes:
* 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.
*
* It is important that the timer start/stop overhead be determined
* when porting or modifying this code.
*
* $Id$
*/
#include <rtems.h>
#include <bsp.h>
#include <at91rm9200.h>
#include <at91rm9200_pmc.h>
uint16_t tstart;
bool benchmark_timer_find_average_overhead;
uint32_t tick_time;
/*
* Set up TC0 -
* timer_clock2 (MCK/8)
* capture mode - this shouldn't matter
*/
void benchmark_timer_initialize( void )
{
uint32_t tmr_freq;
/* since we are using timer_clock2, divide mck by 8 */
tmr_freq = at91rm9200_get_mck() / 8;
TC_TC0_REG(TC_CMR) = TC_CMR_TCCLKS(1); /* timer_clock2 */
TC_TC0_REG(TC_CCR) = (TC_CCR_CLKEN /* enable the counter */
| TC_CCR_SWTRG); /* start it up */
/* tick time in nanoseconds */
tick_time = 1000000000/tmr_freq;
}
/*
* 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 )
{
uint16_t t;
uint32_t total;
t = TC_TC0_REG(TC_CV);
/*
* 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 = t * tick_time;
if ( benchmark_timer_find_average_overhead == 1 )
return total; /* in nanosecond 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;
}
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