shared/timer/timer.c

0001 /**
0002  *  @file
0003  *  @brief IDT 4650 Timer Driver.
0004  *
0005  *  This file manages the benchmark timer used by the RTEMS Timing Test
0006  *  Suite.
0007  */
0008
0009 /*
0010  *  Author:     Craig Lebakken <craigl@transition.com>
0011  *
0012  *  COPYRIGHT (c) 1996 by Transition Networks Inc.
0013  *
0014  *  To anyone who acknowledges that this file is provided "AS IS"
0015  *  without any express or implied warranty:
0016  *      permission to use, copy, modify, and distribute this file
0017  *      for any purpose is hereby granted without fee, provided that
0018  *      the above copyright notice and this notice appears in all
0019  *      copies, and that the name of Transition Networks not be used in
0020  *      advertising or publicity pertaining to distribution of the
0021  *      software without specific, written prior permission.
0022  *      Transition Networks makes no representations about the suitability
0023  *      of this software for any purpose.
0024  *
0025  *  derived from src/lib/libbsp/no_cpu/no_bsp/timer/timer.c
0026  *
0027  *  COPYRIGHT (c) 1989-1999.
0028  *  On-Line Applications Research Corporation (OAR).
0029  *
0030  *  The license and distribution terms for this file may be
0031  *  found in the file LICENSE in this distribution or at
0032  *  http://www.rtems.org/license/LICENSE.
0033  */
0034
0035 #include <rtems.h>
0036 #include <rtems/btimer.h>
0037
0038 #define CLOCKS_PER_MICROSECOND ( CPU_CLOCK_RATE_MHZ )
0039 #define TIMER_MAX_VALUE 0xffffffff
0040
0041 extern uint32_t   mips_read_timer( void );
0042
0043 static bool benchmark_timer_find_average_overhead;
0044 static uint32_t   benchmark_timer_initial_value = 0;
0045
0046 void benchmark_timer_initialize( void )
0047 {
0048    benchmark_timer_initial_value = mips_read_timer();
0049   /*
0050    *  Somehow start the timer
0051    */
0052
0053   /* Timer on 4650 is always running */
0054 }
0055
0056 /*
0057  *  The following controls the behavior of benchmark_timer_read().
0058  *
0059  *  AVG_OVEREHAD is the overhead for starting and stopping the timer.  It
0060  *  is usually deducted from the number returned.
0061  *
0062  *  LEAST_VALID is the lowest number this routine should trust.  Numbers
0063  *  below this are "noise" and zero is returned.
0064  */
0065
0066 #define AVG_OVERHEAD      8  /* It typically takes X.X microseconds */
0067                              /* (Y countdowns) to start/stop the timer. */
0068                              /* This value is in cycles. */
0069 #define LEAST_VALID       1  /* Don't trust a clicks value lower than this */
0070
0071 benchmark_timer_t benchmark_timer_read( void )
0072 {
0073   uint64_t   clicks;
0074   uint32_t   total;
0075
0076   /*
0077    *  Read the timer and see how many clicks it has been since we started.
0078    */
0079
0080   clicks = mips_read_timer();   /* XXX: read some HW here */
0081   if (clicks < benchmark_timer_initial_value)
0082   {
0083       clicks += TIMER_MAX_VALUE;
0084   }
0085   clicks -= benchmark_timer_initial_value;
0086
0087   /*
0088    *  Total is calculated by taking into account the number of timer overflow
0089    *  interrupts since the timer was initialized and clicks since the last
0090    *  interrupts.
0091    */
0092 #if 0 /* leave total in number of cycles */
0093    total = clicks / CLOCKS_PER_MICROSECOND;
0094 #else
0095    total = clicks;
0096 #endif
0097
0098   if ( benchmark_timer_find_average_overhead == 1 )
0099     return total;          /* in # cycles units */
0100   else {
0101     if ( total < LEAST_VALID )
0102       return 0;            /* below timer resolution */
0103   /*
0104    *  leave total in cycles
0105    */
0106       return (total - AVG_OVERHEAD);
0107     }
0108 }
0109
0110 void benchmark_timer_disable_subtracting_average_overhead(bool find_flag)
0111 {
0112   benchmark_timer_find_average_overhead = find_flag;
0113 }