1 | /* timer.c |
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2 | * |
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3 | * This file manages the benchmark timer used by the RTEMS Timing Test |
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4 | * Suite. Each measured time period is demarcated by calls to |
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5 | * Timer_initialize() and Read_timer(). Read_timer() usually returns |
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6 | * the number of microseconds since Timer_initialize() exitted. |
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7 | * |
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8 | * NOTE: It is important that the timer start/stop overhead be |
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9 | * determined when porting or modifying this code. |
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10 | * |
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11 | * COPYRIGHT (c) 1989, 1990, 1991, 1992, 1993, 1994. |
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12 | * On-Line Applications Research Corporation (OAR). |
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13 | * |
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14 | * $Id$ |
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15 | */ |
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16 | |
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17 | #ifndef lint |
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18 | static char _sccsid[] = "@(#)timer.c 05/07/96 1.4\n"; |
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19 | #endif |
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20 | |
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21 | #include <rtems.h> |
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22 | |
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23 | #define CLOCKS_PER_MICROSECOND ( CPU_CLOCK_RATE_MHZ ) |
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24 | #define TIMER_MAX_VALUE 0xffffffff |
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25 | |
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26 | static unsigned32 read_timer( void ) |
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27 | { |
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28 | return 0; /* do something with real hardware here */ |
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29 | } |
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30 | |
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31 | static rtems_boolean Timer_driver_Find_average_overhead; |
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32 | static unsigned32 Timer_initial_value = 0; |
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33 | |
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34 | void Timer_initialize( void ) |
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35 | { |
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36 | Timer_initial_value = read_timer(); |
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37 | |
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38 | /* |
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39 | * Somehow start the timer |
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40 | */ |
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41 | |
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42 | /* Timer is always running */ |
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43 | } |
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44 | |
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45 | /* |
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46 | * The following controls the behavior of Read_timer(). |
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47 | * |
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48 | * AVG_OVEREHAD is the overhead for starting and stopping the timer. It |
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49 | * is usually deducted from the number returned. |
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50 | * |
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51 | * LEAST_VALID is the lowest number this routine should trust. Numbers |
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52 | * below this are "noise" and zero is returned. |
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53 | */ |
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54 | |
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55 | #define AVG_OVERHEAD 8 /* It typically takes X.X microseconds */ |
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56 | /* (Y countdowns) to start/stop the timer. */ |
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57 | /* This value is in cycles. */ |
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58 | #define LEAST_VALID 1 /* Don't trust a clicks value lower than this */ |
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59 | |
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60 | int Read_timer( void ) |
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61 | { |
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62 | unsigned64 clicks; |
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63 | unsigned32 total; |
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64 | |
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65 | /* |
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66 | * Read the timer and see how many clicks it has been since we started. |
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67 | */ |
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68 | |
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69 | clicks = read_timer(); /* XXX: read some HW here */ |
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70 | if (clicks < Timer_initial_value) |
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71 | { |
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72 | clicks += TIMER_MAX_VALUE; |
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73 | } |
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74 | clicks -= Timer_initial_value; |
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75 | |
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76 | /* |
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77 | * Total is calculated by taking into account the number of timer overflow |
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78 | * interrupts since the timer was initialized and clicks since the last |
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79 | * interrupts. |
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80 | */ |
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81 | #if 0 /* leave total in number of cycles */ |
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82 | total = clicks / CLOCKS_PER_MICROSECOND; |
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83 | #else |
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84 | total = clicks; |
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85 | #endif |
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86 | |
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87 | if ( Timer_driver_Find_average_overhead == 1 ) |
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88 | return total; /* in # cycles units */ |
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89 | else { |
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90 | if ( total < LEAST_VALID ) |
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91 | return 0; /* below timer resolution */ |
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92 | /* |
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93 | * leave total in cycles |
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94 | */ |
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95 | return (total - AVG_OVERHEAD); |
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96 | } |
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97 | } |
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98 | |
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99 | /* |
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100 | * Empty function call used in loops to measure basic cost of looping |
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101 | * in Timing Test Suite. |
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102 | */ |
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103 | |
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104 | rtems_status_code Empty_function( void ) |
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105 | { |
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106 | return RTEMS_SUCCESSFUL; |
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107 | } |
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108 | |
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109 | void Set_find_average_overhead( |
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110 | rtems_boolean find_flag |
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111 | ) |
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112 | { |
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113 | Timer_driver_Find_average_overhead = find_flag; |
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114 | } |
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115 | |
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