1 | /* |
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2 | * Watchdog Handler |
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3 | * |
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4 | * |
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5 | * COPYRIGHT (c) 1989-1999. |
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6 | * On-Line Applications Research Corporation (OAR). |
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7 | * |
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8 | * The license and distribution terms for this file may be |
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9 | * found in the file LICENSE in this distribution or at |
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10 | * http://www.rtems.com/license/LICENSE. |
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11 | * |
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12 | * $Id$ |
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13 | */ |
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14 | |
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15 | #if HAVE_CONFIG_H |
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16 | #include "config.h" |
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17 | #endif |
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18 | |
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19 | #include <rtems/system.h> |
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20 | #include <rtems/score/isr.h> |
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21 | #include <rtems/score/watchdog.h> |
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22 | |
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23 | /*PAGE |
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24 | * |
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25 | * _Watchdog_Tickle |
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26 | * |
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27 | * This routine decrements the delta counter in response to a tick. The |
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28 | * delta chain is updated accordingly. |
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29 | * |
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30 | * Input parameters: |
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31 | * header - pointer to the delta chain to be tickled |
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32 | * |
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33 | * Output parameters: NONE |
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34 | */ |
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35 | |
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36 | void _Watchdog_Tickle( |
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37 | Chain_Control *header |
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38 | ) |
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39 | { |
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40 | ISR_Level level; |
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41 | Watchdog_Control *the_watchdog; |
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42 | Watchdog_States watchdog_state; |
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43 | |
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44 | /* |
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45 | * See the comment in watchdoginsert.c and watchdogadjust.c |
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46 | * about why it's safe not to declare header a pointer to |
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47 | * volatile data - till, 2003/7 |
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48 | */ |
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49 | |
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50 | _ISR_Disable( level ); |
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51 | |
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52 | if ( _Chain_Is_empty( header ) ) |
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53 | goto leave; |
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54 | |
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55 | the_watchdog = _Watchdog_First( header ); |
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56 | |
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57 | /* |
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58 | * For some reason, on rare occasions the_watchdog->delta_interval |
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59 | * of the head of the watchdog chain is 0. Before this test was |
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60 | * added, on these occasions an event (which usually was supposed |
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61 | * to have a timeout of 1 tick would have a delta_interval of 0, which |
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62 | * would be decremented to 0xFFFFFFFF by the unprotected |
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63 | * "the_watchdog->delta_interval--;" operation. |
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64 | * This would mean the event would not timeout, and also the chain would |
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65 | * be blocked, because a timeout with a very high number would be at the |
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66 | * head, rather than at the end. |
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67 | * The test "if (the_watchdog->delta_interval != 0)" |
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68 | * here prevents this from occuring. |
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69 | * |
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70 | * We were not able to categorically identify the situation that causes |
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71 | * this, but proved it to be true empirically. So this check causes |
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72 | * correct behaviour in this circumstance. |
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73 | * |
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74 | * The belief is that a race condition exists whereby an event at the head |
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75 | * of the chain is removed (by a pending ISR or higher priority task) |
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76 | * during the _ISR_Flash( level ); in _Watchdog_Insert, but the watchdog |
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77 | * to be inserted has already had its delta_interval adjusted to 0, and |
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78 | * so is added to the head of the chain with a delta_interval of 0. |
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79 | * |
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80 | * Steven Johnson - 12/2005 (gcc-3.2.3 -O3 on powerpc) |
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81 | */ |
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82 | if (the_watchdog->delta_interval != 0) { |
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83 | the_watchdog->delta_interval--; |
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84 | if ( the_watchdog->delta_interval != 0 ) |
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85 | goto leave; |
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86 | } |
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87 | |
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88 | do { |
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89 | watchdog_state = _Watchdog_Remove( the_watchdog ); |
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90 | |
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91 | _ISR_Enable( level ); |
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92 | |
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93 | switch( watchdog_state ) { |
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94 | case WATCHDOG_ACTIVE: |
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95 | (*the_watchdog->routine)( |
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96 | the_watchdog->id, |
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97 | the_watchdog->user_data |
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98 | ); |
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99 | break; |
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100 | |
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101 | case WATCHDOG_INACTIVE: |
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102 | /* |
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103 | * This state indicates that the watchdog is not on any chain. |
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104 | * Thus, it is NOT on a chain being tickled. This case should |
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105 | * never occur. |
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106 | */ |
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107 | break; |
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108 | |
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109 | case WATCHDOG_BEING_INSERTED: |
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110 | /* |
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111 | * This state indicates that the watchdog is in the process of |
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112 | * BEING inserted on the chain. Thus, it can NOT be on a chain |
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113 | * being tickled. This case should never occur. |
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114 | */ |
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115 | break; |
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116 | |
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117 | case WATCHDOG_REMOVE_IT: |
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118 | break; |
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119 | } |
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120 | |
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121 | _ISR_Disable( level ); |
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122 | |
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123 | the_watchdog = _Watchdog_First( header ); |
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124 | } while ( !_Chain_Is_empty( header ) && |
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125 | (the_watchdog->delta_interval == 0) ); |
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126 | |
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127 | leave: |
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128 | _ISR_Enable(level); |
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129 | } |
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