1 | /* timer.c |
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2 | * |
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3 | * This file contains the initialization code for the IDT 4650 timer driver. |
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4 | * |
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5 | * Author: Craig Lebakken <craigl@transition.com> |
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6 | * |
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7 | * COPYRIGHT (c) 1996 by Transition Networks Inc. |
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8 | * |
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9 | * To anyone who acknowledges that this file is provided "AS IS" |
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10 | * without any express or implied warranty: |
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11 | * permission to use, copy, modify, and distribute this file |
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12 | * for any purpose is hereby granted without fee, provided that |
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13 | * the above copyright notice and this notice appears in all |
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14 | * copies, and that the name of Transition Networks not be used in |
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15 | * advertising or publicity pertaining to distribution of the |
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16 | * software without specific, written prior permission. |
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17 | * Transition Networks makes no representations about the suitability |
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18 | * of this software for any purpose. |
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19 | * |
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20 | * derived from src/lib/libbsp/no_cpu/no_bsp/timer/timer.c |
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21 | * |
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22 | * This file manages the benchmark timer used by the RTEMS Timing Test |
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23 | * Suite. Each measured time period is demarcated by calls to |
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24 | * benchmark_timer_initialize() and benchmark_timer_read(). benchmark_timer_read() usually returns |
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25 | * the number of microseconds since benchmark_timer_initialize() exitted. |
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26 | * |
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27 | * NOTE: It is important that the timer start/stop overhead be |
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28 | * determined when porting or modifying this code. |
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29 | * |
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30 | * COPYRIGHT (c) 1989-1999. |
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31 | * On-Line Applications Research Corporation (OAR). |
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32 | * |
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33 | * The license and distribution terms for this file may be |
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34 | * found in the file LICENSE in this distribution or at |
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35 | * http://www.rtems.org/license/LICENSE. |
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36 | */ |
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37 | |
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38 | /* |
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39 | * Rather than deleting this, it is commented out to (hopefully) help |
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40 | * the submitter send updates. |
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41 | * |
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42 | * static char _sccsid[] = "@(#)timer.c 08/20/96 1.5\n"; |
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43 | */ |
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44 | |
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45 | |
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46 | #include <rtems.h> |
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47 | |
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48 | #define CLOCKS_PER_MICROSECOND ( CPU_CLOCK_RATE_MHZ ) |
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49 | #define TIMER_MAX_VALUE 0xffffffff |
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50 | |
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51 | extern uint32_t mips_read_timer( void ); |
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52 | |
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53 | static bool benchmark_timer_find_average_overhead; |
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54 | static uint32_t benchmark_timer_initial_value = 0; |
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55 | |
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56 | void benchmark_timer_initialize( void ) |
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57 | { |
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58 | benchmark_timer_initial_value = mips_read_timer(); |
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59 | /* |
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60 | * Somehow start the timer |
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61 | */ |
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62 | |
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63 | /* Timer on 4650 is always running */ |
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64 | } |
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65 | |
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66 | /* |
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67 | * The following controls the behavior of benchmark_timer_read(). |
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68 | * |
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69 | * AVG_OVEREHAD is the overhead for starting and stopping the timer. It |
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70 | * is usually deducted from the number returned. |
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71 | * |
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72 | * LEAST_VALID is the lowest number this routine should trust. Numbers |
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73 | * below this are "noise" and zero is returned. |
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74 | */ |
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75 | |
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76 | #define AVG_OVERHEAD 8 /* It typically takes X.X microseconds */ |
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77 | /* (Y countdowns) to start/stop the timer. */ |
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78 | /* This value is in cycles. */ |
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79 | #define LEAST_VALID 1 /* Don't trust a clicks value lower than this */ |
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80 | |
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81 | int benchmark_timer_read( void ) |
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82 | { |
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83 | uint64_t clicks; |
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84 | uint32_t total; |
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85 | |
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86 | /* |
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87 | * Read the timer and see how many clicks it has been since we started. |
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88 | */ |
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89 | |
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90 | clicks = mips_read_timer(); /* XXX: read some HW here */ |
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91 | if (clicks < benchmark_timer_initial_value) |
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92 | { |
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93 | clicks += TIMER_MAX_VALUE; |
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94 | } |
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95 | clicks -= benchmark_timer_initial_value; |
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96 | |
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97 | /* |
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98 | * Total is calculated by taking into account the number of timer overflow |
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99 | * interrupts since the timer was initialized and clicks since the last |
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100 | * interrupts. |
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101 | */ |
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102 | #if 0 /* leave total in number of cycles */ |
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103 | total = clicks / CLOCKS_PER_MICROSECOND; |
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104 | #else |
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105 | total = clicks; |
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106 | #endif |
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107 | |
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108 | if ( benchmark_timer_find_average_overhead == 1 ) |
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109 | return total; /* in # cycles units */ |
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110 | else { |
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111 | if ( total < LEAST_VALID ) |
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112 | return 0; /* below timer resolution */ |
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113 | /* |
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114 | * leave total in cycles |
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115 | */ |
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116 | return (total - AVG_OVERHEAD); |
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117 | } |
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118 | } |
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119 | |
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120 | void benchmark_timer_disable_subtracting_average_overhead(bool find_flag) |
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121 | { |
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122 | benchmark_timer_find_average_overhead = find_flag; |
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123 | } |
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