1 | @c |
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2 | @c COPYRIGHT (c) 1988-2002. |
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3 | @c On-Line Applications Research Corporation (OAR). |
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4 | @c All rights reserved. |
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5 | @c |
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6 | @c $Id$ |
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7 | @c |
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8 | |
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9 | @chapter Signal Manager |
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10 | |
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11 | @cindex signals |
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12 | |
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13 | @section Introduction |
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14 | |
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15 | The signal manager provides the capabilities required |
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16 | for asynchronous communication. The directives provided by the |
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17 | signal manager are: |
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18 | |
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19 | @itemize @bullet |
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20 | @item @code{@value{DIRPREFIX}signal_catch} - Establish an ASR |
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21 | @item @code{@value{DIRPREFIX}signal_send} - Send signal set to a task |
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22 | @end itemize |
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23 | |
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24 | @section Background |
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25 | |
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26 | @subsection Signal Manager Definitions |
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27 | |
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28 | @cindex asynchronous signal routine |
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29 | @cindex ASR |
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30 | |
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31 | The signal manager allows a task to optionally define |
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32 | an asynchronous signal routine (ASR). An ASR is to a task what |
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33 | an ISR is to an application's set of tasks. When the processor |
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34 | is interrupted, the execution of an application is also |
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35 | interrupted and an ISR is given control. Similarly, when a |
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36 | signal is sent to a task, that task's execution path will be |
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37 | "interrupted" by the ASR. Sending a signal to a task has no |
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38 | effect on the receiving task's current execution state. |
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39 | |
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40 | @findex rtems_signal_set |
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41 | |
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42 | A signal flag is used by a task (or ISR) to inform |
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43 | another task of the occurrence of a significant situation. |
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44 | Thirty-two signal flags are associated with each task. A |
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45 | collection of one or more signals is referred to as a signal |
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46 | set. The data type @code{@value{DIRPREFIX}signal_set} |
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47 | is used to manipulate signal sets. |
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48 | |
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49 | A signal set is posted when it is directed (or sent) to a |
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50 | task. A pending signal is a signal that has been sent to a task |
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51 | with a valid ASR, but has not been processed by that task's ASR. |
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52 | |
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53 | |
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54 | @subsection A Comparison of ASRs and ISRs |
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55 | |
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56 | @cindex ASR vs. ISR |
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57 | @cindex ISR vs. ASR |
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58 | |
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59 | The format of an ASR is similar to that of an ISR |
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60 | with the following exceptions: |
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61 | |
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62 | @itemize @bullet |
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63 | @item ISRs are scheduled by the processor hardware. ASRs are |
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64 | scheduled by RTEMS. |
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65 | |
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66 | @item ISRs do not execute in the context of a task and may |
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67 | invoke only a subset of directives. ASRs execute in the context |
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68 | of a task and may execute any directive. |
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69 | |
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70 | @item When an ISR is invoked, it is passed the vector number |
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71 | as its argument. When an ASR is invoked, it is passed the |
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72 | signal set as its argument. |
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73 | |
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74 | @item An ASR has a task mode which can be different from that |
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75 | of the task. An ISR does not execute as a task and, as a |
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76 | result, does not have a task mode. |
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77 | @end itemize |
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78 | |
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79 | @subsection Building a Signal Set |
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80 | |
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81 | @cindex signal set, building |
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82 | |
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83 | A signal set is built by a bitwise OR of the desired |
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84 | signals. The set of valid signals is @code{@value{RPREFIX}SIGNAL_0} through |
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85 | @code{@value{RPREFIX}SIGNAL_31}. If a signal is not explicitly specified in the |
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86 | signal set, then it is not present. Signal values are |
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87 | specifically designed to be mutually exclusive, therefore |
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88 | bitwise OR and addition operations are equivalent as long as |
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89 | each signal appears exactly once in the component list. |
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90 | |
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91 | This example demonstrates the signal parameter used |
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92 | when sending the signal set consisting of |
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93 | @code{@value{RPREFIX}SIGNAL_6}, |
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94 | @code{@value{RPREFIX}SIGNAL_15}, and |
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95 | @code{@value{RPREFIX}SIGNAL_31}. The signal parameter provided |
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96 | to the @code{@value{DIRPREFIX}signal_send} directive should be |
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97 | @code{@value{RPREFIX}SIGNAL_6 @value{OR} |
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98 | @value{RPREFIX}SIGNAL_15 @value{OR} @value{RPREFIX}SIGNAL_31}. |
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99 | |
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100 | @subsection Building an ASR Mode |
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101 | |
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102 | @cindex ASR mode, building |
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103 | |
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104 | In general, an ASR's mode is built by a bitwise OR of |
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105 | the desired mode components. The set of valid mode components |
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106 | is the same as those allowed with the task_create and task_mode |
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107 | directives. A complete list of mode options is provided in the |
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108 | following table: |
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109 | |
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110 | @itemize @bullet |
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111 | @item @code{@value{RPREFIX}PREEMPT} is masked by |
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112 | @code{@value{RPREFIX}PREEMPT_MASK} and enables preemption |
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113 | |
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114 | @item @code{@value{RPREFIX}NO_PREEMPT} is masked by |
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115 | @code{@value{RPREFIX}PREEMPT_MASK} and disables preemption |
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116 | |
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117 | @item @code{@value{RPREFIX}NO_TIMESLICE} is masked by |
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118 | @code{@value{RPREFIX}TIMESLICE_MASK} and disables timeslicing |
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119 | |
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120 | @item @code{@value{RPREFIX}TIMESLICE} is masked by |
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121 | @code{@value{RPREFIX}TIMESLICE_MASK} and enables timeslicing |
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122 | |
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123 | @item @code{@value{RPREFIX}ASR} is masked by |
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124 | @code{@value{RPREFIX}ASR_MASK} and enables ASR processing |
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125 | |
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126 | @item @code{@value{RPREFIX}NO_ASR} is masked by |
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127 | @code{@value{RPREFIX}ASR_MASK} and disables ASR processing |
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128 | |
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129 | @item @code{@value{RPREFIX}INTERRUPT_LEVEL(0)} is masked by |
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130 | @code{@value{RPREFIX}INTERRUPT_MASK} and enables all interrupts |
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131 | |
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132 | @item @code{@value{RPREFIX}INTERRUPT_LEVEL(n)} is masked by |
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133 | @code{@value{RPREFIX}INTERRUPT_MASK} and sets interrupts level n |
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134 | @end itemize |
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135 | |
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136 | Mode values are specifically designed to be mutually |
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137 | exclusive, therefore bitwise OR and addition operations are |
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138 | equivalent as long as each mode appears exactly once in the |
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139 | component list. A mode component listed as a default is not |
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140 | required to appear in the mode list, although it is a good |
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141 | programming practice to specify default components. If all |
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142 | defaults are desired, the mode DEFAULT_MODES should be specified |
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143 | on this call. |
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144 | |
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145 | This example demonstrates the mode parameter used |
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146 | with the @code{@value{DIRPREFIX}signal_catch} |
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147 | to establish an ASR which executes at |
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148 | interrupt level three and is non-preemptible. The mode should |
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149 | be set to |
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150 | @code{@value{RPREFIX}INTERRUPT_LEVEL(3) @value{OR} @value{RPREFIX}NO_PREEMPT} |
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151 | to indicate the |
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152 | desired processor mode and interrupt level. |
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153 | |
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154 | @section Operations |
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155 | |
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156 | @subsection Establishing an ASR |
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157 | |
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158 | The @code{@value{DIRPREFIX}signal_catch} directive establishes an ASR for the |
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159 | calling task. The address of the ASR and its execution mode are |
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160 | specified to this directive. The ASR's mode is distinct from |
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161 | the task's mode. For example, the task may allow preemption, |
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162 | while that task's ASR may have preemption disabled. Until a |
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163 | task calls @code{@value{DIRPREFIX}signal_catch} the first time, |
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164 | its ASR is invalid, and no signal sets can be sent to the task. |
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165 | |
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166 | A task may invalidate its ASR and discard all pending |
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167 | signals by calling @code{@value{DIRPREFIX}signal_catch} |
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168 | with a value of NULL for the ASR's address. When a task's |
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169 | ASR is invalid, new signal sets sent to this task are discarded. |
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170 | |
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171 | A task may disable ASR processing (@code{@value{RPREFIX}NO_ASR}) via the |
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172 | task_mode directive. When a task's ASR is disabled, the signals |
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173 | sent to it are left pending to be processed later when the ASR |
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174 | is enabled. |
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175 | |
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176 | Any directive that can be called from a task can also |
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177 | be called from an ASR. A task is only allowed one active ASR. |
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178 | Thus, each call to @code{@value{DIRPREFIX}signal_catch} |
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179 | replaces the previous one. |
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180 | |
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181 | Normally, signal processing is disabled for the ASR's |
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182 | execution mode, but if signal processing is enabled for the ASR, |
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183 | the ASR must be reentrant. |
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184 | |
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185 | @subsection Sending a Signal Set |
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186 | |
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187 | The @code{@value{DIRPREFIX}signal_send} directive allows both |
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188 | tasks and ISRs to send signals to a target task. The target task and |
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189 | a set of signals are specified to the |
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190 | @code{@value{DIRPREFIX}signal_send} directive. The sending |
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191 | of a signal to a task has no effect on the execution state of |
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192 | that task. If the task is not the currently running task, then |
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193 | the signals are left pending and processed by the task's ASR the |
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194 | next time the task is dispatched to run. The ASR is executed |
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195 | immediately before the task is dispatched. If the currently |
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196 | running task sends a signal to itself or is sent a signal from |
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197 | an ISR, its ASR is immediately dispatched to run provided signal |
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198 | processing is enabled. |
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199 | |
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200 | If an ASR with signals enabled is preempted by |
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201 | another task or an ISR and a new signal set is sent, then a new |
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202 | copy of the ASR will be invoked, nesting the preempted ASR. |
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203 | Upon completion of processing the new signal set, control will |
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204 | return to the preempted ASR. In this situation, the ASR must be |
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205 | reentrant. |
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206 | |
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207 | Like events, identical signals sent to a task are not |
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208 | queued. In other words, sending the same signal multiple times |
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209 | to a task (without any intermediate signal processing occurring |
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210 | for the task), has the same result as sending that signal to |
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211 | that task once. |
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212 | |
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213 | @subsection Processing an ASR |
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214 | |
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215 | Asynchronous signals were designed to provide the |
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216 | capability to generate software interrupts. The processing of |
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217 | software interrupts parallels that of hardware interrupts. As a |
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218 | result, the differences between the formats of ASRs and ISRs is |
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219 | limited to the meaning of the single argument passed to an ASR. |
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220 | The ASR should have the following calling sequence and adhere to |
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221 | @value{LANGUAGE} calling conventions: |
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222 | |
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223 | @ifset is-C |
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224 | @findex rtems_asr |
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225 | @example |
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226 | rtems_asr user_routine( |
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227 | rtems_signal_set signals |
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228 | ); |
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229 | @end example |
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230 | @end ifset |
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231 | |
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232 | @ifset is-Ada |
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233 | @example |
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234 | procedure User_Routine ( |
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235 | Signals : in RTEMS.Signal_Set |
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236 | ); |
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237 | @end example |
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238 | @end ifset |
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239 | |
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240 | When the ASR returns to RTEMS the mode and execution |
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241 | path of the interrupted task (or ASR) is restored to the context |
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242 | prior to entering the ASR. |
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243 | |
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244 | @section Directives |
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245 | |
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246 | This section details the signal manager's directives. |
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247 | A subsection is dedicated to each of this manager's directives |
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248 | and describes the calling sequence, related constants, usage, |
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249 | and status codes. |
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250 | |
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251 | @c |
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252 | @c |
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253 | @c |
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254 | @page |
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255 | @subsection SIGNAL_CATCH - Establish an ASR |
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256 | |
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257 | @cindex establish an ASR |
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258 | @cindex install an ASR |
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259 | |
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260 | @subheading CALLING SEQUENCE: |
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261 | |
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262 | @ifset is-C |
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263 | @findex rtems_signal_catch |
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264 | @example |
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265 | rtems_status_code rtems_signal_catch( |
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266 | rtems_asr_entry asr_handler, |
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267 | rtems_mode mode |
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268 | ); |
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269 | @end example |
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270 | @end ifset |
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271 | |
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272 | @ifset is-Ada |
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273 | @example |
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274 | procedure Signal_Catch ( |
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275 | ASR_Handler : in RTEMS.ASR_Handler; |
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276 | Mode_Set : in RTEMS.Mode; |
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277 | Result : out RTEMS.Status_Codes |
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278 | ); |
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279 | @end example |
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280 | @end ifset |
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281 | |
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282 | @subheading DIRECTIVE STATUS CODES: |
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283 | @code{@value{RPREFIX}SUCCESSFUL} - always successful |
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284 | |
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285 | @subheading DESCRIPTION: |
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286 | |
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287 | This directive establishes an asynchronous signal |
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288 | routine (ASR) for the calling task. The asr_handler parameter |
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289 | specifies the entry point of the ASR. If asr_handler is NULL, |
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290 | the ASR for the calling task is invalidated and all pending |
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291 | signals are cleared. Any signals sent to a task with an invalid |
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292 | ASR are discarded. The mode parameter specifies the execution |
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293 | mode for the ASR. This execution mode supersedes the task's |
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294 | execution mode while the ASR is executing. |
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295 | |
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296 | @subheading NOTES: |
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297 | |
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298 | This directive will not cause the calling task to be |
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299 | preempted. |
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300 | |
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301 | The following task mode constants are defined by RTEMS: |
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302 | |
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303 | @itemize @bullet |
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304 | @item @code{@value{RPREFIX}PREEMPT} is masked by |
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305 | @code{@value{RPREFIX}PREEMPT_MASK} and enables preemption |
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306 | |
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307 | @item @code{@value{RPREFIX}NO_PREEMPT} is masked by |
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308 | @code{@value{RPREFIX}PREEMPT_MASK} and disables preemption |
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309 | |
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310 | @item @code{@value{RPREFIX}NO_TIMESLICE} is masked by |
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311 | @code{@value{RPREFIX}TIMESLICE_MASK} and disables timeslicing |
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312 | |
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313 | @item @code{@value{RPREFIX}TIMESLICE} is masked by |
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314 | @code{@value{RPREFIX}TIMESLICE_MASK} and enables timeslicing |
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315 | |
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316 | @item @code{@value{RPREFIX}ASR} is masked by |
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317 | @code{@value{RPREFIX}ASR_MASK} and enables ASR processing |
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318 | |
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319 | @item @code{@value{RPREFIX}NO_ASR} is masked by |
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320 | @code{@value{RPREFIX}ASR_MASK} and disables ASR processing |
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321 | |
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322 | @item @code{@value{RPREFIX}INTERRUPT_LEVEL(0)} is masked by |
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323 | @code{@value{RPREFIX}INTERRUPT_MASK} and enables all interrupts |
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324 | |
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325 | @item @code{@value{RPREFIX}INTERRUPT_LEVEL(n)} is masked by |
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326 | @code{@value{RPREFIX}INTERRUPT_MASK} and sets interrupts level n |
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327 | @end itemize |
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328 | |
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329 | @c |
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330 | @c |
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331 | @c |
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332 | @page |
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333 | @subsection SIGNAL_SEND - Send signal set to a task |
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334 | |
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335 | @cindex send signal set |
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336 | |
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337 | @subheading CALLING SEQUENCE: |
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338 | |
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339 | @ifset is-C |
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340 | @findex rtems_signal_send |
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341 | @example |
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342 | rtems_status_code rtems_signal_send( |
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343 | rtems_id id, |
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344 | rtems_signal_set signal_set |
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345 | ); |
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346 | @end example |
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347 | @end ifset |
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348 | |
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349 | @ifset is-Ada |
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350 | @example |
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351 | procedure Signal_Send ( |
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352 | ID : in RTEMS.ID; |
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353 | Signal_Set : in RTEMS.Signal_Set; |
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354 | Result : out RTEMS.Status_Codes |
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355 | ); |
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356 | @end example |
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357 | @end ifset |
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358 | |
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359 | @subheading DIRECTIVE STATUS CODES: |
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360 | @code{@value{RPREFIX}SUCCESSFUL} - signal sent successfully@* |
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361 | @code{@value{RPREFIX}INVALID_ID} - task id invalid@* |
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362 | @code{@value{RPREFIX}NOT_DEFINED} - ASR invalid |
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363 | |
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364 | @subheading DESCRIPTION: |
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365 | |
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366 | This directive sends a signal set to the task |
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367 | specified in id. The signal_set parameter contains the signal |
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368 | set to be sent to the task. |
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369 | |
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370 | If a caller sends a signal set to a task with an |
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371 | invalid ASR, then an error code is returned to the caller. If a |
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372 | caller sends a signal set to a task whose ASR is valid but |
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373 | disabled, then the signal set will be caught and left pending |
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374 | for the ASR to process when it is enabled. If a caller sends a |
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375 | signal set to a task with an ASR that is both valid and enabled, |
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376 | then the signal set is caught and the ASR will execute the next |
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377 | time the task is dispatched to run. |
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378 | |
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379 | @subheading NOTES: |
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380 | |
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381 | Sending a signal set to a task has no effect on that |
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382 | task's state. If a signal set is sent to a blocked task, then |
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383 | the task will remain blocked and the signals will be processed |
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384 | when the task becomes the running task. |
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385 | |
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386 | Sending a signal set to a global task which does not |
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387 | reside on the local node will generate a request telling the |
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388 | remote node to send the signal set to the specified task. |
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389 | |
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