source: rtems/c/src/lib/libbsp/m68k/gen68302/timer/timer.c @ 08311cc3

/*  Timer_init()
 *
 *  This routine initializes TIMER 2 for an MC68302.
 *
 *  Input parameters:  NONE
 *
 *  Output parameters:  NONE
 *
 *  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>
#include "m68302.h"


#define TMR2_VAL 0x071b /* Timer mode register
                         * (section 3.5.2.1 in 68302 manual)
                         * 15-8: "7"    prescaler divide by 8 (x+1)
                         *  7-6: 00     dis. intr. on capture event
                         *    5:  0     active-low pulse
                         *    4:  1     intr. on reaching reference
                         *    3:  1     restart counter on reference
                         *  2-1: 01     master clock input source
                         *    0:  1     enable timer
                         */
#define TRR2_VAL 2000   /* Timer reference register
                         * (section 3.5.2.2 in 68302 manual)
                         * 2000 ticks @ (16MHz/1)/8 = 1-ms count
                         */

rtems_unsigned32 Timer_interrupts;

rtems_boolean Timer_driver_Find_average_overhead;

rtems_isr timerisr();

void Timer_initialize( void )
{
    m302.reg.tmr2 = 0;                  /* disable timer */

    Timer_interrupts = 0;               /* clear timer ISR count */

    m302.reg.trr2 = TRR2_VAL;           /* set timer reference register */
    m302.reg.tmr2 = TMR2_VAL;           /* set timer mode register */
    m302.reg.imr |= RBIT_IMR_TIMER2;    /* set 68302 int-mask to allow ints */
}

/*
 *  The following controls the behavior of Read_timer().
 *
 *  FIND_AVG_OVERHEAD *  instructs the routine to return the "raw" count.
 *
 *  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 */

/*
 * Return timer value in 1/2-microsecond units
 */
int Read_timer( void )
{
  rtems_unsigned16 clicks;
  rtems_unsigned32 total;

  /*
   *  Read the timer and see how many clicks it has been since counter
   *  rolled over.
   */

  clicks = m302.reg.tcn2;

  /*
   *  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 = (Timer_interrupts * TRR2_VAL) + clicks;

  if ( Timer_driver_Find_average_overhead == 1 )
    return total;          /* in XXX microsecond units */

  if ( total < LEAST_VALID )
    return 0;            /* below timer resolution */

  /*
   *  Convert 1/2-microsecond count into microseconds
   */

  return (total - AVG_OVERHEAD) >> 1;
}


/*
 *  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;
}