1 | .. comment SPDX-License-Identifier: CC-BY-SA-4.0 |
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2 | |
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3 | .. COMMENT: COPYRIGHT (c) 1988-2008. |
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4 | .. COMMENT: On-Line Applications Research Corporation (OAR). |
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5 | .. COMMENT: All rights reserved. |
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6 | |
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7 | .. index:: timers |
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8 | |
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9 | Timer Manager |
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10 | ************* |
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11 | |
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12 | Introduction |
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13 | ============ |
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14 | |
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15 | The timer manager provides support for timer |
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16 | facilities. The directives provided by the timer manager are: |
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17 | |
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18 | - rtems_timer_create_ - Create a timer |
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19 | |
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20 | - rtems_timer_ident_ - Get ID of a timer |
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21 | |
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22 | - rtems_timer_cancel_ - Cancel a timer |
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23 | |
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24 | - rtems_timer_delete_ - Delete a timer |
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25 | |
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26 | - rtems_timer_fire_after_ - Fire timer after interval |
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27 | |
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28 | - rtems_timer_fire_when_ - Fire timer when specified |
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29 | |
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30 | - rtems_timer_initiate_server_ - Initiate server for task-based timers |
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31 | |
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32 | - rtems_timer_server_fire_after_ - Fire task-based timer after interval |
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33 | |
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34 | - rtems_timer_server_fire_when_ - Fire task-based timer when specified |
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35 | |
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36 | - rtems_timer_reset_ - Reset an interval timer |
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37 | |
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38 | Background |
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39 | ========== |
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40 | |
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41 | Required Support |
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42 | ---------------- |
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43 | |
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44 | A clock tick is required to support the functionality provided by this manager. |
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45 | |
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46 | Timers |
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47 | ------ |
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48 | |
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49 | A timer is an RTEMS object which allows the application to schedule operations |
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50 | to occur at specific times in the future. User supplied timer service routines |
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51 | are invoked by either a clock tick directive or a special Timer |
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52 | Server task when the timer fires. Timer service routines may perform any |
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53 | operations or directives which normally would be performed by the application |
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54 | code which invoked a clock tick directive. |
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55 | |
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56 | The timer can be used to implement watchdog routines which only fire to denote |
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57 | that an application error has occurred. The timer is reset at specific points |
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58 | in the application to ensure that the watchdog does not fire. Thus, if the |
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59 | application does not reset the watchdog timer, then the timer service routine |
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60 | will fire to indicate that the application has failed to reach a reset point. |
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61 | This use of a timer is sometimes referred to as a "keep alive" or a "deadman" |
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62 | timer. |
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63 | |
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64 | Timer Server |
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65 | ------------ |
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66 | |
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67 | The Timer Server task is responsible for executing the timer service routines |
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68 | associated with all task-based timers. This task executes at a priority |
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69 | specified by :ref:`rtems_timer_initiate_server() <rtems_timer_initiate_server>` |
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70 | and it may have a priority of zero (the highest priority). In uniprocessor |
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71 | configurations, it is created non-preemptible. |
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72 | |
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73 | By providing a mechanism where timer service routines execute in task rather |
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74 | than interrupt space, the application is allowed a bit more flexibility in what |
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75 | operations a timer service routine can perform. For example, the Timer Server |
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76 | can be configured to have a floating point context in which case it would be |
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77 | safe to perform floating point operations from a task-based timer. Most of the |
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78 | time, executing floating point instructions from an interrupt service routine |
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79 | is not considered safe. The timer service routines invoked by the Timer Server |
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80 | may block, however, since this blocks the Timer Server itself, other timer |
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81 | service routines that are already pending do not run until the blocked timer |
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82 | service routine finished its work. |
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83 | |
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84 | The Timer Server is designed to remain blocked until a task-based timer fires. |
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85 | This reduces the execution overhead of the Timer Server. |
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86 | |
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87 | .. index:: rtems_timer_service_routine |
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88 | |
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89 | Timer Service Routines |
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90 | ---------------------- |
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91 | |
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92 | The timer service routine should adhere to C calling conventions and have a |
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93 | prototype similar to the following: |
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94 | |
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95 | .. code-block:: c |
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96 | |
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97 | rtems_timer_service_routine user_routine( |
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98 | rtems_id timer_id, |
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99 | void *user_data |
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100 | ); |
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101 | |
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102 | Where the timer_id parameter is the RTEMS object ID of the timer which is being |
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103 | fired and user_data is a pointer to user-defined information which may be |
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104 | utilized by the timer service routine. The argument user_data may be NULL. |
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105 | |
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106 | Operations |
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107 | ========== |
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108 | |
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109 | Creating a Timer |
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110 | ---------------- |
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111 | |
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112 | The ``rtems_timer_create`` directive creates a timer by allocating a Timer |
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113 | Control Block (TMCB), assigning the timer a user-specified name, and assigning |
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114 | it a timer ID. Newly created timers do not have a timer service routine |
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115 | associated with them and are not active. |
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116 | |
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117 | Obtaining Timer IDs |
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118 | ------------------- |
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119 | |
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120 | When a timer is created, RTEMS generates a unique timer ID and assigns it to |
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121 | the created timer until it is deleted. The timer ID may be obtained by either |
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122 | of two methods. First, as the result of an invocation of the |
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123 | ``rtems_timer_create`` directive, the timer ID is stored in a user provided |
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124 | location. Second, the timer ID may be obtained later using the |
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125 | ``rtems_timer_ident`` directive. The timer ID is used by other directives to |
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126 | manipulate this timer. |
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127 | |
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128 | Initiating an Interval Timer |
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129 | ---------------------------- |
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130 | |
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131 | The ``rtems_timer_fire_after`` and ``rtems_timer_server_fire_after`` directives |
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132 | initiate a timer to fire a user provided timer service routine after the |
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133 | specified number of clock ticks have elapsed. When the interval has elapsed, |
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134 | the timer service routine will be invoked from a clock tick |
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135 | directive if it was initiated by the ``rtems_timer_fire_after`` directive and |
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136 | from the Timer Server task if initiated by the |
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137 | ``rtems_timer_server_fire_after`` directive. |
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138 | |
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139 | Initiating a Time of Day Timer |
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140 | ------------------------------ |
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141 | |
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142 | The ``rtems_timer_fire_when`` and ``rtems_timer_server_fire_when`` directive |
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143 | initiate a timer to fire a user provided timer service routine when the |
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144 | specified time of day has been reached. When the interval has elapsed, the |
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145 | timer service routine will be invoked from a clock tick directive |
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146 | by the ``rtems_timer_fire_when`` directive and from the Timer Server task if |
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147 | initiated by the ``rtems_timer_server_fire_when`` directive. |
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148 | |
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149 | Canceling a Timer |
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150 | ----------------- |
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151 | |
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152 | The ``rtems_timer_cancel`` directive is used to halt the specified timer. Once |
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153 | canceled, the timer service routine will not fire unless the timer is |
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154 | reinitiated. The timer can be reinitiated using the ``rtems_timer_reset``, |
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155 | ``rtems_timer_fire_after``, and ``rtems_timer_fire_when`` directives. |
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156 | |
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157 | Resetting a Timer |
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158 | ----------------- |
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159 | |
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160 | The ``rtems_timer_reset`` directive is used to restore an interval timer |
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161 | initiated by a previous invocation of ``rtems_timer_fire_after`` or |
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162 | ``rtems_timer_server_fire_after`` to its original interval length. If the |
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163 | timer has not been used or the last usage of this timer was by the |
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164 | ``rtems_timer_fire_when`` or ``rtems_timer_server_fire_when`` directive, then |
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165 | an error is returned. The timer service routine is not changed or fired by |
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166 | this directive. |
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167 | |
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168 | Initiating the Timer Server |
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169 | --------------------------- |
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170 | |
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171 | The ``rtems_timer_initiate_server`` directive is used to allocate and start the |
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172 | execution of the Timer Server task. The application can specify both the stack |
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173 | size and attributes of the Timer Server. The Timer Server executes at a |
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174 | priority higher than any application task and thus the user can expect to be |
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175 | preempted as the result of executing the ``rtems_timer_initiate_server`` |
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176 | directive. |
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177 | |
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178 | Deleting a Timer |
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179 | ---------------- |
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180 | |
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181 | The ``rtems_timer_delete`` directive is used to delete a timer. If the timer |
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182 | is running and has not expired, the timer is automatically canceled. The |
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183 | timer's control block is returned to the TMCB free list when it is deleted. A |
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184 | timer can be deleted by a task other than the task which created the timer. |
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185 | Any subsequent references to the timer's name and ID are invalid. |
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186 | |
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187 | Directives |
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188 | ========== |
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189 | |
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190 | This section details the timer manager's directives. A subsection is dedicated |
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191 | to each of this manager's directives and describes the calling sequence, |
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192 | related constants, usage, and status codes. |
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193 | |
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194 | .. raw:: latex |
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195 | |
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196 | \clearpage |
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197 | .. index:: create a timer |
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198 | .. index:: rtems_timer_create |
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199 | |
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200 | .. _rtems_timer_create: |
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201 | |
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202 | TIMER_CREATE - Create a timer |
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203 | ----------------------------- |
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204 | |
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205 | CALLING SEQUENCE: |
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206 | .. code-block:: c |
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207 | |
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208 | rtems_status_code rtems_timer_create( |
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209 | rtems_name name, |
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210 | rtems_id *id |
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211 | ); |
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212 | |
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213 | DIRECTIVE STATUS CODES: |
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214 | .. list-table:: |
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215 | :class: rtems-table |
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216 | |
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217 | * - ``RTEMS_SUCCESSFUL`` |
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218 | - timer created successfully |
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219 | * - ``RTEMS_INVALID_ADDRESS`` |
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220 | - ``id`` is NULL |
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221 | * - ``RTEMS_INVALID_NAME`` |
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222 | - invalid timer name |
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223 | * - ``RTEMS_TOO_MANY`` |
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224 | - too many timers created |
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225 | |
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226 | DESCRIPTION: |
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227 | This directive creates a timer. The assigned timer id is returned in id. |
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228 | This id is used to access the timer with other timer manager directives. |
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229 | For control and maintenance of the timer, RTEMS allocates a TMCB from the |
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230 | local TMCB free pool and initializes it. |
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231 | |
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232 | NOTES: |
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233 | This directive will obtain the allocator mutex and may cause the calling |
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234 | task to be preempted. |
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235 | |
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236 | In SMP configurations, the processor of the currently executing thread |
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237 | determines the processor used for the created timer. During the life-time |
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238 | of the timer this processor is used to manage the timer internally. |
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239 | |
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240 | .. raw:: latex |
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241 | |
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242 | \clearpage |
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243 | |
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244 | .. index:: obtain the ID of a timer |
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245 | .. index:: rtems_timer_ident |
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246 | |
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247 | .. _rtems_timer_ident: |
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248 | |
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249 | TIMER_IDENT - Get ID of a timer |
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250 | ------------------------------- |
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251 | |
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252 | CALLING SEQUENCE: |
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253 | .. code-block:: c |
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254 | |
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255 | rtems_status_code rtems_timer_ident( |
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256 | rtems_name name, |
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257 | rtems_id *id |
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258 | ); |
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259 | |
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260 | DIRECTIVE STATUS CODES: |
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261 | .. list-table:: |
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262 | :class: rtems-table |
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263 | |
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264 | * - ``RTEMS_SUCCESSFUL`` |
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265 | - timer identified successfully |
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266 | * - ``RTEMS_INVALID_ADDRESS`` |
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267 | - ``id`` is NULL |
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268 | * - ``RTEMS_INVALID_NAME`` |
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269 | - timer name not found |
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270 | |
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271 | DESCRIPTION: |
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272 | This directive obtains the timer id associated with the timer name to be |
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273 | acquired. If the timer name is not unique, then the timer id will match |
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274 | one of the timers with that name. However, this timer id is not guaranteed |
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275 | to correspond to the desired timer. The timer id is used to access this |
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276 | timer in other timer related directives. |
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277 | |
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278 | NOTES: |
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279 | This directive will not cause the running task to be preempted. |
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280 | |
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281 | .. raw:: latex |
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282 | |
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283 | \clearpage |
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284 | |
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285 | .. index:: cancel a timer |
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286 | .. index:: rtems_timer_cancel |
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287 | |
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288 | .. _rtems_timer_cancel: |
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289 | |
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290 | TIMER_CANCEL - Cancel a timer |
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291 | ----------------------------- |
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292 | |
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293 | CALLING SEQUENCE: |
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294 | .. code-block:: c |
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295 | |
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296 | rtems_status_code rtems_timer_cancel( |
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297 | rtems_id id |
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298 | ); |
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299 | |
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300 | DIRECTIVE STATUS CODES: |
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301 | .. list-table:: |
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302 | :class: rtems-table |
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303 | |
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304 | * - ``RTEMS_SUCCESSFUL`` |
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305 | - timer canceled successfully |
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306 | * - ``RTEMS_INVALID_ID`` |
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307 | - invalid timer id |
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308 | |
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309 | DESCRIPTION: |
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310 | This directive cancels the timer id. This timer will be reinitiated by the |
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311 | next invocation of ``rtems_timer_reset``, ``rtems_timer_fire_after``, or |
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312 | ``rtems_timer_fire_when`` with this id. |
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313 | |
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314 | NOTES: |
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315 | This directive will not cause the running task to be preempted. |
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316 | |
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317 | .. raw:: latex |
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318 | |
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319 | \clearpage |
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320 | |
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321 | .. index:: delete a timer |
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322 | .. index:: rtems_timer_delete |
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323 | |
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324 | .. _rtems_timer_delete: |
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325 | |
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326 | TIMER_DELETE - Delete a timer |
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327 | ----------------------------- |
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328 | |
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329 | CALLING SEQUENCE: |
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330 | .. code-block:: c |
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331 | |
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332 | rtems_status_code rtems_timer_delete( |
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333 | rtems_id id |
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334 | ); |
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335 | |
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336 | DIRECTIVE STATUS CODES: |
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337 | .. list-table:: |
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338 | :class: rtems-table |
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339 | |
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340 | * - ``RTEMS_SUCCESSFUL`` |
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341 | - timer deleted successfully |
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342 | * - ``RTEMS_INVALID_ID`` |
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343 | - invalid timer id |
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344 | |
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345 | DESCRIPTION: |
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346 | This directive deletes the timer specified by id. If the timer is running, |
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347 | it is automatically canceled. The TMCB for the deleted timer is reclaimed |
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348 | by RTEMS. |
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349 | |
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350 | NOTES: |
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351 | This directive will obtain the allocator mutex and may cause the calling |
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352 | task to be preempted. |
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353 | |
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354 | A timer can be deleted by a task other than the task which created the |
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355 | timer. |
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356 | |
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357 | .. raw:: latex |
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358 | |
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359 | \clearpage |
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360 | |
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361 | .. index:: fire a timer after an interval |
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362 | .. index:: rtems_timer_fire_after |
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363 | |
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364 | .. _rtems_timer_fire_after: |
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365 | |
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366 | TIMER_FIRE_AFTER - Fire timer after interval |
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367 | -------------------------------------------- |
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368 | |
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369 | CALLING SEQUENCE: |
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370 | .. code-block:: c |
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371 | |
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372 | rtems_status_code rtems_timer_fire_after( |
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373 | rtems_id id, |
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374 | rtems_interval ticks, |
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375 | rtems_timer_service_routine_entry routine, |
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376 | void *user_data |
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377 | ); |
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378 | |
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379 | DIRECTIVE STATUS CODES: |
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380 | .. list-table:: |
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381 | :class: rtems-table |
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382 | |
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383 | * - ``RTEMS_SUCCESSFUL`` |
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384 | - timer initiated successfully |
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385 | * - ``RTEMS_INVALID_ADDRESS`` |
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386 | - ``routine`` is NULL |
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387 | * - ``RTEMS_INVALID_ID`` |
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388 | - invalid timer id |
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389 | * - ``RTEMS_INVALID_NUMBER`` |
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390 | - invalid interval |
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391 | |
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392 | DESCRIPTION: |
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393 | This directive initiates the timer specified by id. If the timer is |
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394 | running, it is automatically canceled before being initiated. The timer is |
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395 | scheduled to fire after an interval ticks clock ticks has passed. When the |
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396 | timer fires, the timer service routine routine will be invoked with the |
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397 | argument user_data. |
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398 | |
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399 | NOTES: |
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400 | This directive will not cause the running task to be preempted. |
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401 | |
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402 | .. raw:: latex |
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403 | |
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404 | \clearpage |
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405 | |
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406 | .. index:: fire a timer at wall time |
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407 | .. index:: rtems_timer_fire_when |
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408 | |
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409 | .. _rtems_timer_fire_when: |
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410 | |
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411 | TIMER_FIRE_WHEN - Fire timer when specified |
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412 | ------------------------------------------- |
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413 | |
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414 | CALLING SEQUENCE: |
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415 | .. code-block:: c |
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416 | |
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417 | rtems_status_code rtems_timer_fire_when( |
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418 | rtems_id id, |
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419 | rtems_time_of_day *wall_time, |
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420 | rtems_timer_service_routine_entry routine, |
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421 | void *user_data |
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422 | ); |
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423 | |
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424 | DIRECTIVE STATUS CODES: |
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425 | .. list-table:: |
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426 | :class: rtems-table |
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427 | |
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428 | * - ``RTEMS_SUCCESSFUL`` |
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429 | - timer initiated successfully |
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430 | * - ``RTEMS_INVALID_ADDRESS`` |
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431 | - ``routine`` is NULL |
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432 | * - ``RTEMS_INVALID_ADDRESS`` |
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433 | - ``wall_time`` is NULL |
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434 | * - ``RTEMS_INVALID_ID`` |
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435 | - invalid timer id |
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436 | * - ``RTEMS_NOT_DEFINED`` |
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437 | - system date and time is not set |
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438 | * - ``RTEMS_INVALID_CLOCK`` |
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439 | - invalid time of day |
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440 | |
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441 | DESCRIPTION: |
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442 | This directive initiates the timer specified by id. If the timer is |
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443 | running, it is automatically canceled before being initiated. The timer is |
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444 | scheduled to fire at the time of day specified by wall_time. When the |
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445 | timer fires, the timer service routine routine will be invoked with the |
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446 | argument user_data. |
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447 | |
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448 | NOTES: |
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449 | This directive will not cause the running task to be preempted. |
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450 | |
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451 | .. raw:: latex |
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452 | |
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453 | \clearpage |
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454 | |
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455 | .. index:: initiate the Timer Server |
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456 | .. index:: rtems_timer_initiate_server |
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457 | |
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458 | .. _rtems_timer_initiate_server: |
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459 | |
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460 | TIMER_INITIATE_SERVER - Initiate server for task-based timers |
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461 | ------------------------------------------------------------- |
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462 | |
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463 | CALLING SEQUENCE: |
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464 | .. code-block:: c |
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465 | |
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466 | rtems_status_code rtems_timer_initiate_server( |
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467 | uint32_t priority, |
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468 | uint32_t stack_size, |
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469 | rtems_attribute attribute_set |
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470 | ); |
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471 | |
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472 | DIRECTIVE STATUS CODES: |
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473 | .. list-table:: |
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474 | :class: rtems-table |
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475 | |
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476 | * - ``RTEMS_SUCCESSFUL`` |
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477 | - Timer Server initiated successfully |
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478 | * - ``RTEMS_TOO_MANY`` |
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479 | - too many tasks created |
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480 | |
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481 | DESCRIPTION: |
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482 | This directive initiates the Timer Server task. This task is responsible |
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483 | for executing all timers initiated via the |
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484 | ``rtems_timer_server_fire_after`` or ``rtems_timer_server_fire_when`` |
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485 | directives. |
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486 | |
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487 | NOTES: |
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488 | This directive could cause the calling task to be preempted. |
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489 | |
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490 | The Timer Server task is created using the ``rtems_task_create`` service |
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491 | and must be accounted for when configuring the system. |
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492 | |
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493 | Even through this directive invokes the ``rtems_task_create`` and |
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494 | ``rtems_task_start`` directives, it should only fail due to resource |
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495 | allocation problems. |
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496 | |
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497 | .. raw:: latex |
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498 | |
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499 | \clearpage |
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500 | |
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501 | .. index:: fire task-based a timer after an interval |
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502 | .. index:: rtems_timer_server_fire_after |
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503 | |
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504 | .. _rtems_timer_server_fire_after: |
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505 | |
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506 | TIMER_SERVER_FIRE_AFTER - Fire task-based timer after interval |
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507 | -------------------------------------------------------------- |
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508 | |
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509 | CALLING SEQUENCE: |
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510 | .. code-block:: c |
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511 | |
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512 | rtems_status_code rtems_timer_server_fire_after( |
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513 | rtems_id id, |
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514 | rtems_interval ticks, |
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515 | rtems_timer_service_routine_entry routine, |
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516 | void *user_data |
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517 | ); |
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518 | |
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519 | DIRECTIVE STATUS CODES: |
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520 | .. list-table:: |
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521 | :class: rtems-table |
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522 | |
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523 | * - ``RTEMS_SUCCESSFUL`` |
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524 | - timer initiated successfully |
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525 | * - ``RTEMS_INVALID_ADDRESS`` |
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526 | - ``routine`` is NULL |
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527 | * - ``RTEMS_INVALID_ID`` |
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528 | - invalid timer id |
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529 | * - ``RTEMS_INVALID_NUMBER`` |
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530 | - invalid interval |
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531 | * - ``RTEMS_INCORRECT_STATE`` |
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532 | - Timer Server not initiated |
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533 | |
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534 | DESCRIPTION: |
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535 | This directive initiates the timer specified by id and specifies that when |
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536 | it fires it will be executed by the Timer Server. |
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537 | |
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538 | If the timer is running, it is automatically canceled before being |
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539 | initiated. The timer is scheduled to fire after an interval ticks clock |
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540 | ticks has passed. When the timer fires, the timer service routine routine |
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541 | will be invoked with the argument user_data. |
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542 | |
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543 | NOTES: |
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544 | This directive will not cause the running task to be preempted. |
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545 | |
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546 | .. raw:: latex |
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547 | |
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548 | \clearpage |
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549 | |
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550 | .. index:: fire a task-based timer at wall time |
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551 | .. index:: rtems_timer_server_fire_when |
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552 | |
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553 | .. _rtems_timer_server_fire_when: |
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554 | |
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555 | TIMER_SERVER_FIRE_WHEN - Fire task-based timer when specified |
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556 | ------------------------------------------------------------- |
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557 | |
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558 | CALLING SEQUENCE: |
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559 | .. code-block:: c |
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560 | |
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561 | rtems_status_code rtems_timer_server_fire_when( |
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562 | rtems_id id, |
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563 | rtems_time_of_day *wall_time, |
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564 | rtems_timer_service_routine_entry routine, |
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565 | void *user_data |
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566 | ); |
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567 | |
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568 | DIRECTIVE STATUS CODES: |
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569 | .. list-table:: |
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570 | :class: rtems-table |
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571 | |
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572 | * - ``RTEMS_SUCCESSFUL`` |
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573 | - timer initiated successfully |
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574 | * - ``RTEMS_INVALID_ADDRESS`` |
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575 | - ``routine`` is NULL |
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576 | * - ``RTEMS_INVALID_ADDRESS`` |
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577 | - ``wall_time`` is NULL |
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578 | * - ``RTEMS_INVALID_ID`` |
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579 | - invalid timer id |
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580 | * - ``RTEMS_NOT_DEFINED`` |
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581 | - system date and time is not set |
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582 | * - ``RTEMS_INVALID_CLOCK`` |
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583 | - invalid time of day |
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584 | * - ``RTEMS_INCORRECT_STATE`` |
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585 | - Timer Server not initiated |
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586 | |
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587 | DESCRIPTION: |
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588 | This directive initiates the timer specified by id and specifies that when |
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589 | it fires it will be executed by the Timer Server. |
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590 | |
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591 | If the timer is running, it is automatically canceled before being |
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592 | initiated. The timer is scheduled to fire at the time of day specified by |
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593 | wall_time. When the timer fires, the timer service routine routine will be |
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594 | invoked with the argument user_data. |
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595 | |
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596 | NOTES: |
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597 | This directive will not cause the running task to be preempted. |
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598 | |
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599 | .. raw:: latex |
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600 | |
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601 | \clearpage |
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602 | |
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603 | .. index:: reset a timer |
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604 | .. index:: rtems_timer_reset |
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605 | |
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606 | .. _rtems_timer_reset: |
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607 | |
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608 | TIMER_RESET - Reset an interval timer |
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609 | ------------------------------------- |
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610 | |
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611 | CALLING SEQUENCE: |
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612 | .. code-block:: c |
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613 | |
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614 | rtems_status_code rtems_timer_reset( |
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615 | rtems_id id |
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616 | ); |
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617 | |
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618 | DIRECTIVE STATUS CODES: |
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619 | .. list-table:: |
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620 | :class: rtems-table |
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621 | |
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622 | * - ``RTEMS_SUCCESSFUL`` |
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623 | - timer reset successfully |
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624 | * - ``RTEMS_INVALID_ID`` |
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625 | - invalid timer id |
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626 | * - ``RTEMS_NOT_DEFINED`` |
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627 | - attempted to reset a when or newly created timer |
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628 | |
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629 | DESCRIPTION: |
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630 | This directive resets the timer associated with id. This timer must have |
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631 | been previously initiated with either the ``rtems_timer_fire_after`` or |
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632 | ``rtems_timer_server_fire_after`` directive. If active the timer is |
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633 | canceled, after which the timer is reinitiated using the same interval and |
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634 | timer service routine which the original ``rtems_timer_fire_after`` or |
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635 | ``rtems_timer_server_fire_after`` directive used. |
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636 | |
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637 | NOTES: |
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638 | If the timer has not been used or the last usage of this timer was by a |
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639 | ``rtems_timer_fire_when`` or ``rtems_timer_server_fire_when`` directive, |
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640 | then the ``RTEMS_NOT_DEFINED`` error is returned. |
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641 | |
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642 | Restarting a cancelled after timer results in the timer being reinitiated |
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643 | with its previous timer service routine and interval. |
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644 | |
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645 | This directive will not cause the running task to be preempted. |
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