source: rtems/c/src/lib/libbsp/m68k/efi68k/timer/timer.c @ 9b64c2d5

4.104.114.84.95
Last change on this file since 9b64c2d5 was 60b791ad, checked in by Joel Sherrill <joel.sherrill@…>, on Feb 17, 1998 at 11:46:28 PM

updated copyright to 1998

  • Property mode set to 100644
File size: 3.2 KB
Line 
1/*  Timer_init()
2 *
3 *  This routine initializes a timer in efi68k's DP8570A TCP
4 *
5 *  Input parameters:  NONE
6 *
7 *  Output parameters:  NONE
8 *
9 *  NOTE: It is important that the timer start/stop overhead be
10 *        determined when porting or modifying this code.
11 *
12 *  COPYRIGHT (c) 1989-1998.
13 *  On-Line Applications Research Corporation (OAR).
14 *  Copyright assigned to U.S. Government, 1994.
15 *
16 *  The license and distribution terms for this file may be
17 *  found in the file LICENSE in this distribution or at
18 *  http://www.OARcorp.com/rtems/license.html.
19 *
20 *  $Id$
21 */
22
23
24#include <bsp.h>
25
26rtems_boolean Timer_driver_Find_average_overhead;
27
28extern rtems_isr Clock_isr();
29
30void Timer_initialize( void )
31{
32  /* stop counter */
33  *MSR = 0;
34  *T0CR = 0;
35
36  /*
37   * Make sure isr is installed
38   */
39
40  set_vector( Clock_isr, TCP_ISR_LEVEL+24, 1);
41
42  /* clear timer ISR count */
43  Timer_interrupts = 0;
44
45  /* load count (count down timer) */
46  *MSR = 0;
47  *T0_MSB = 0xff;
48  *T0_LSB = 0xff;
49
50  /* clear old interrupts */
51  *MSR = T0;
52
53  /* enable timer 0 interrupt */
54  *MSR = RS;
55  *ICR0 |= T0E;
56
57  /*
58     TSS = 1        starts the timer (timer resets on start)
59     M1/0 = 0/1     rate generator
60     C2/1/0 = 0/0/0 external clock (8MHz) (1/8 usec resolution)
61     RD = 0         read data (latchs count)
62     CHG = 0        hold
63   */
64  *MSR = 0;
65  *T0CR = (TSS | M0);
66}
67
68/*
69 *  The following controls the behavior of Read_timer().
70 *
71 *  FIND_AVG_OVERHEAD *  instructs the routine to return the "raw" count.
72 *
73 *  AVG_OVEREHAD is the overhead for starting and stopping the timer.  It
74 *  is usually deducted from the number returned.
75 *
76 *  LEAST_VALID is the lowest number this routine should trust.  Numbers
77 *  below this are "noise" and zero is returned.
78 */
79
80#define AVG_OVERHEAD      0  /* It typically takes X.X microseconds */
81                             /* (Y countdowns) to start/stop the timer. */
82                             /* This value is in microseconds. */
83#define LEAST_VALID       1  /* Don't trust a clicks value lower than this */
84
85/*
86 * Return timer value in 1/2-microsecond units
87 */
88int Read_timer( void )
89{
90  rtems_unsigned16 clicks;
91  rtems_unsigned32 total;
92  rtems_unsigned32 msb, lsb;
93
94
95  /*
96   *  Read the timer and see how many clicks it has been since counter
97   *  rolled over.
98   */
99
100  *MSR = 0;
101  *T0CR |= RD;
102  /* must read MSB first */ 
103  msb = *T0_MSB;
104  lsb = *T0_LSB;
105  clicks = 0xffff - ((msb << 8) | lsb);
106
107  /*
108   *  Total is calculated by taking into account the number of timer overflow
109   *  interrupts since the timer was initialized and clicks since the last
110   *  interrupts.
111   */
112
113  total = (Timer_interrupts * 0x10000 + clicks + 4)/8; /* in micoseconds */
114  /*                                            ^^^ round to nearest int */
115
116  if ( Timer_driver_Find_average_overhead == 1 )
117    return total;          /* in XXX microsecond units */
118
119  if ( total < LEAST_VALID )
120    return 0;            /* below timer resolution */
121
122  return (total - AVG_OVERHEAD);
123}
124
125
126/*
127 *  Empty function call used in loops to measure basic cost of looping
128 *  in Timing Test Suite.
129 */
130
131rtems_status_code Empty_function(void)
132{
133    return RTEMS_SUCCESSFUL;
134}
135
136void Set_find_average_overhead(
137  rtems_boolean find_flag
138)
139{
140  Timer_driver_Find_average_overhead = find_flag;
141}
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