source: rtems/c/src/lib/libbsp/arm/edb7312/timer/timer.c @ 8fbe2e6

/*
 * Cirrus EP7312 Timer driver
 *
 * Copyright (c) 2002 by Jay Monkman <jtm@smoothsmoothie.com>
 *
 *  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.
 *
 * 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.
*/

#include <rtems.h>
#include <bsp.h>
#include <rtems/btimer.h>
#include <ep7312.h>

uint16_t         tstart;
bool benchmark_timer_find_average_overhead;

void benchmark_timer_initialize( void )
{
    *EP7312_SYSCON1 |= EP7312_SYSCON1_TC2_512KHZ;
    *EP7312_TC2D = 0xffff;
}

/*
 *  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 */

benchmark_timer_t benchmark_timer_read( void )
{
  uint16_t         t;
  uint32_t         total;
  t = *EP7312_TC2D;

  /*
   *  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 = (uint32_t)0x0000ffff - t;  /* result is 1/512000 = ~2 uS */
  total = (total * 1953) / 1000;   /* convert to uS */
  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;
}