1 | .. comment SPDX-License-Identifier: CC-BY-SA-4.0 |
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2 | |
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3 | .. Copyright (C) 1988, 2008 On-Line Applications Research Corporation (OAR) |
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4 | |
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5 | .. index:: regions |
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6 | |
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7 | Region Manager |
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8 | ************** |
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9 | |
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10 | Introduction |
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11 | ============ |
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12 | |
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13 | The region manager provides facilities to dynamically allocate memory in |
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14 | variable sized units. The directives provided by the region manager are: |
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15 | |
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16 | - rtems_region_create_ - Create a region |
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17 | |
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18 | - rtems_region_ident_ - Get ID of a region |
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19 | |
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20 | - rtems_region_delete_ - Delete a region |
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21 | |
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22 | - rtems_region_extend_ - Add memory to a region |
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23 | |
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24 | - rtems_region_get_segment_ - Get segment from a region |
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25 | |
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26 | - rtems_region_return_segment_ - Return segment to a region |
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27 | |
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28 | - rtems_region_get_segment_size_ - Obtain size of a segment |
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29 | |
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30 | - rtems_region_resize_segment_ - Change size of a segment |
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31 | |
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32 | Background |
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33 | ========== |
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34 | |
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35 | .. index:: region, definition |
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36 | .. index:: segment, definition |
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37 | |
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38 | Region Manager Definitions |
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39 | -------------------------- |
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40 | |
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41 | A region makes up a physically contiguous memory space with user-defined |
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42 | boundaries from which variable-sized segments are dynamically allocated and |
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43 | deallocated. A segment is a variable size section of memory which is allocated |
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44 | in multiples of a user-defined page size. This page size is required to be a |
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45 | multiple of four greater than or equal to four. For example, if a request for |
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46 | a 350-byte segment is made in a region with 256-byte pages, then a 512-byte |
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47 | segment is allocated. |
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48 | |
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49 | Regions are organized as doubly linked chains of variable sized memory blocks. |
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50 | Memory requests are allocated using a first-fit algorithm. If available, the |
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51 | requester receives the number of bytes requested (rounded up to the next page |
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52 | size). RTEMS requires some overhead from the region's memory for each segment |
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53 | that is allocated. Therefore, an application should only modify the memory of |
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54 | a segment that has been obtained from the region. The application should NOT |
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55 | modify the memory outside of any obtained segments and within the region's |
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56 | boundaries while the region is currently active in the system. |
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57 | |
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58 | Upon return to the region, the free block is coalesced with its neighbors (if |
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59 | free) on both sides to produce the largest possible unused block. |
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60 | |
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61 | .. index:: region attribute set, building |
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62 | |
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63 | Building an Attribute Set |
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64 | ------------------------- |
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65 | |
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66 | In general, an attribute set is built by a bitwise OR of the desired attribute |
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67 | components. The set of valid region attributes is provided in the following |
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68 | table: |
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69 | |
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70 | .. list-table:: |
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71 | :class: rtems-table |
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72 | |
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73 | * - ``RTEMS_FIFO`` |
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74 | - tasks wait by FIFO (default) |
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75 | * - ``RTEMS_PRIORITY`` |
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76 | - tasks wait by priority |
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77 | |
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78 | Attribute values are specifically designed to be mutually exclusive, therefore |
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79 | bitwise OR and addition operations are equivalent as long as each attribute |
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80 | appears exactly once in the component list. An attribute listed as a default |
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81 | is not required to appear in the attribute list, although it is a good |
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82 | programming practice to specify default attributes. If all defaults are |
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83 | desired, the attribute ``RTEMS_DEFAULT_ATTRIBUTES`` should be specified on this |
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84 | call. |
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85 | |
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86 | This example demonstrates the attribute_set parameter needed to create a region |
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87 | with the task priority waiting queue discipline. The attribute_set parameter |
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88 | to the ``rtems_region_create`` directive should be ``RTEMS_PRIORITY``. |
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89 | |
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90 | Building an Option Set |
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91 | ---------------------- |
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92 | |
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93 | In general, an option is built by a bitwise OR of the desired option |
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94 | components. The set of valid options for the ``rtems_region_get_segment`` |
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95 | directive are listed in the following table: |
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96 | |
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97 | .. list-table:: |
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98 | :class: rtems-table |
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99 | |
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100 | * - ``RTEMS_WAIT`` |
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101 | - task will wait for segment (default) |
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102 | * - ``RTEMS_NO_WAIT`` |
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103 | - task should not wait |
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104 | |
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105 | Option values are specifically designed to be mutually exclusive, therefore |
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106 | bitwise OR and addition operations are equivalent as long as each option |
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107 | appears exactly once in the component list. An option listed as a default is |
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108 | not required to appear in the option list, although it is a good programming |
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109 | practice to specify default options. If all defaults are desired, the |
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110 | option ``RTEMS_DEFAULT_OPTIONS`` should be specified on this call. |
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111 | |
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112 | This example demonstrates the option parameter needed to poll for a segment. |
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113 | The option parameter passed to the ``rtems_region_get_segment`` directive |
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114 | should be ``RTEMS_NO_WAIT``. |
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115 | |
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116 | Operations |
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117 | ========== |
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118 | |
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119 | Creating a Region |
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120 | ----------------- |
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121 | |
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122 | The ``rtems_region_create`` directive creates a region with the user-defined |
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123 | name. The user may select FIFO or task priority as the method for placing |
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124 | waiting tasks in the task wait queue. RTEMS allocates a Region Control Block |
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125 | (RNCB) from the RNCB free list to maintain the newly created region. RTEMS |
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126 | also generates a unique region ID which is returned to the calling task. |
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127 | |
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128 | It is not possible to calculate the exact number of bytes available to the user |
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129 | since RTEMS requires overhead for each segment allocated. For example, a |
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130 | region with one segment that is the size of the entire region has more |
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131 | available bytes than a region with two segments that collectively are the size |
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132 | of the entire region. This is because the region with one segment requires |
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133 | only the overhead for one segment, while the other region requires the overhead |
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134 | for two segments. |
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135 | |
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136 | Due to automatic coalescing, the number of segments in the region dynamically |
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137 | changes. Therefore, the total overhead required by RTEMS dynamically changes. |
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138 | |
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139 | Obtaining Region IDs |
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140 | -------------------- |
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141 | |
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142 | When a region is created, RTEMS generates a unique region ID and assigns it to |
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143 | the created region until it is deleted. The region ID may be obtained by |
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144 | either of two methods. First, as the result of an invocation of the |
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145 | ``rtems_region_create`` directive, the region ID is stored in a user provided |
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146 | location. Second, the region ID may be obtained later using the |
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147 | ``rtems_region_ident`` directive. The region ID is used by other region |
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148 | manager directives to access this region. |
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149 | |
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150 | Adding Memory to a Region |
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151 | ------------------------- |
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152 | |
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153 | The ``rtems_region_extend`` directive may be used to add memory to an existing |
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154 | region. The caller specifies the size in bytes and starting address of the |
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155 | memory being added. |
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156 | |
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157 | Acquiring a Segment |
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158 | ------------------- |
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159 | |
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160 | The ``rtems_region_get_segment`` directive attempts to acquire a segment from a |
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161 | specified region. If the region has enough available free memory, then a |
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162 | segment is returned successfully to the caller. When the segment cannot be |
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163 | allocated, one of the following situations applies: |
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164 | |
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165 | - By default, the calling task will wait forever to acquire the segment. |
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166 | |
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167 | - Specifying the ``RTEMS_NO_WAIT`` option forces an immediate return with an |
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168 | error status code. |
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169 | |
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170 | - Specifying a timeout limits the interval the task will wait before returning |
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171 | with an error status code. |
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172 | |
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173 | If the task waits for the segment, then it is placed in the region's task wait |
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174 | queue in either FIFO or task priority order. All tasks waiting on a region are |
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175 | returned an error when the message queue is deleted. |
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176 | |
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177 | Releasing a Segment |
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178 | ------------------- |
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179 | |
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180 | When a segment is returned to a region by the ``rtems_region_return_segment`` |
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181 | directive, it is merged with its unallocated neighbors to form the largest |
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182 | possible segment. The first task on the wait queue is examined to determine if |
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183 | its segment request can now be satisfied. If so, it is given a segment and |
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184 | unblocked. This process is repeated until the first task's segment request |
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185 | cannot be satisfied. |
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186 | |
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187 | Obtaining the Size of a Segment |
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188 | ------------------------------- |
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189 | |
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190 | The ``rtems_region_get_segment_size`` directive returns the size in bytes of |
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191 | the specified segment. The size returned includes any "extra" memory included |
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192 | in the segment because of rounding up to a page size boundary. |
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193 | |
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194 | Changing the Size of a Segment |
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195 | ------------------------------ |
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196 | |
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197 | The ``rtems_region_resize_segment`` directive is used to change the size in |
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198 | bytes of the specified segment. The size may be increased or decreased. When |
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199 | increasing the size of a segment, it is possible that the request cannot be |
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200 | satisfied. This directive provides functionality similar to the ``realloc()`` |
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201 | function in the Standard C Library. |
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202 | |
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203 | Deleting a Region |
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204 | ----------------- |
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205 | |
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206 | A region can be removed from the system and returned to RTEMS with the |
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207 | ``rtems_region_delete`` directive. When a region is deleted, its control block |
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208 | is returned to the RNCB free list. A region with segments still allocated is |
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209 | not allowed to be deleted. Any task attempting to do so will be returned an |
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210 | error. As a result of this directive, all tasks blocked waiting to obtain a |
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211 | segment from the region will be readied and returned a status code which |
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212 | indicates that the region was deleted. |
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213 | |
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214 | Directives |
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215 | ========== |
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216 | |
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217 | This section details the region manager's directives. A subsection is |
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218 | dedicated to each of this manager's directives and describes the calling |
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219 | sequence, related constants, usage, and status codes. |
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220 | |
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221 | .. raw:: latex |
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222 | |
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223 | \clearpage |
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224 | |
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225 | .. index:: create a region |
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226 | |
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227 | .. _rtems_region_create: |
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228 | |
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229 | REGION_CREATE - Create a region |
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230 | ------------------------------- |
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231 | |
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232 | CALLING SEQUENCE: |
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233 | .. code-block:: c |
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234 | |
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235 | rtems_status_code rtems_region_create( |
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236 | rtems_name name, |
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237 | void *starting_address, |
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238 | uintptr_t length, |
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239 | uintptr_t page_size, |
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240 | rtems_attribute attribute_set, |
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241 | rtems_id *id |
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242 | ); |
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243 | |
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244 | DIRECTIVE STATUS CODES: |
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245 | .. list-table:: |
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246 | :class: rtems-table |
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247 | |
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248 | * - ``RTEMS_SUCCESSFUL`` |
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249 | - region created successfully |
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250 | * - ``RTEMS_INVALID_NAME`` |
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251 | - invalid region name |
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252 | * - ``RTEMS_INVALID_ADDRESS`` |
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253 | - ``id`` is NULL |
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254 | * - ``RTEMS_INVALID_ADDRESS`` |
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255 | - ``starting_address`` is NULL |
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256 | * - ``RTEMS_TOO_MANY`` |
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257 | - too many regions created |
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258 | * - ``RTEMS_INVALID_SIZE`` |
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259 | - invalid page size |
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260 | * - ``RTEMS_INVALID_SIZE`` |
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261 | - the memory area defined by the starting address and the length |
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262 | parameters is too small |
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263 | |
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264 | DESCRIPTION: |
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265 | This directive creates a region from a contiguous memory area |
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266 | which starts at starting_address and is length bytes long. The memory area |
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267 | must be large enough to contain some internal region administration data. |
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268 | Segments allocated from the region will be a multiple of page_size bytes in |
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269 | length. The specified page size will be aligned to an |
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270 | architecture-specific minimum alignment if necessary. |
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271 | |
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272 | The assigned region id is returned in id. This region id is used as an |
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273 | argument to other region related directives to access the region. |
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274 | |
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275 | For control and maintenance of the region, RTEMS allocates and initializes |
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276 | an RNCB from the RNCB free pool. Thus memory from the region is not used |
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277 | to store the RNCB. However, some overhead within the region is required by |
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278 | RTEMS each time a segment is constructed in the region. |
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279 | |
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280 | Specifying ``RTEMS_PRIORITY`` in attribute_set causes tasks waiting for a |
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281 | segment to be serviced according to task priority. Specifying |
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282 | ``RTEMS_FIFO`` in attribute_set or selecting ``RTEMS_DEFAULT_ATTRIBUTES`` |
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283 | will cause waiting tasks to be serviced in First In-First Out order. |
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284 | |
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285 | NOTES: |
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286 | This directive will obtain the allocator mutex and may cause the calling |
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287 | task to be preempted. |
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288 | |
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289 | The following region attribute constants are defined by RTEMS: |
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290 | |
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291 | .. list-table:: |
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292 | :class: rtems-table |
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293 | |
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294 | * - ``RTEMS_FIFO`` |
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295 | - tasks wait by FIFO (default) |
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296 | * - ``RTEMS_PRIORITY`` |
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297 | - tasks wait by priority |
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298 | |
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299 | .. raw:: latex |
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300 | |
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301 | \clearpage |
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302 | |
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303 | .. index:: get ID of a region |
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304 | .. index:: obtain ID of a region |
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305 | .. index:: rtems_region_ident |
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306 | |
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307 | .. _rtems_region_ident: |
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308 | |
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309 | REGION_IDENT - Get ID of a region |
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310 | --------------------------------- |
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311 | |
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312 | CALLING SEQUENCE: |
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313 | .. code-block:: c |
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314 | |
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315 | rtems_status_code rtems_region_ident( |
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316 | rtems_name name, |
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317 | rtems_id *id |
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318 | ); |
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319 | |
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320 | DIRECTIVE STATUS CODES: |
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321 | .. list-table:: |
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322 | :class: rtems-table |
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323 | |
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324 | * - ``RTEMS_SUCCESSFUL`` |
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325 | - region identified successfully |
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326 | * - ``RTEMS_INVALID_ADDRESS`` |
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327 | - ``id`` is NULL |
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328 | * - ``RTEMS_INVALID_NAME`` |
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329 | - region name not found |
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330 | |
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331 | DESCRIPTION: |
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332 | |
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333 | This directive obtains the region id associated with the region name to be |
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334 | acquired. If the region name is not unique, then the region id will match |
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335 | one of the regions with that name. However, this region id is not |
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336 | guaranteed to correspond to the desired region. The region id is used to |
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337 | access this region in other region manager directives. |
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338 | |
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339 | NOTES: |
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340 | This directive will not cause the running task to be preempted. |
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341 | |
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342 | .. raw:: latex |
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343 | |
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344 | \clearpage |
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345 | |
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346 | .. index:: delete a region |
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347 | .. index:: rtems_region_delete |
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348 | |
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349 | .. _rtems_region_delete: |
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350 | |
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351 | REGION_DELETE - Delete a region |
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352 | ------------------------------- |
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353 | |
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354 | CALLING SEQUENCE: |
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355 | .. code-block:: c |
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356 | |
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357 | rtems_status_code rtems_region_delete( |
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358 | rtems_id id |
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359 | ); |
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360 | |
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361 | DIRECTIVE STATUS CODES: |
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362 | .. list-table:: |
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363 | :class: rtems-table |
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364 | |
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365 | * - ``RTEMS_SUCCESSFUL`` |
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366 | - region deleted successfully |
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367 | * - ``RTEMS_INVALID_ID`` |
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368 | - invalid region id |
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369 | * - ``RTEMS_RESOURCE_IN_USE`` |
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370 | - segments still in use |
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371 | |
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372 | DESCRIPTION: |
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373 | This directive deletes the region specified by id. The region cannot be |
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374 | deleted if any of its segments are still allocated. The RNCB for the |
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375 | deleted region is reclaimed by RTEMS. |
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376 | |
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377 | NOTES: |
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378 | This directive will obtain the allocator mutex and may cause the calling |
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379 | task to be preempted. |
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380 | |
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381 | The calling task does not have to be the task that created the region. Any |
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382 | local task that knows the region id can delete the region. |
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383 | |
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384 | .. raw:: latex |
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385 | |
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386 | \clearpage |
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387 | |
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388 | .. index:: add memory to a region |
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389 | .. index:: region, add memory |
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390 | .. index:: rtems_region_extend |
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391 | |
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392 | .. _rtems_region_extend: |
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393 | |
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394 | REGION_EXTEND - Add memory to a region |
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395 | -------------------------------------- |
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396 | |
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397 | CALLING SEQUENCE: |
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398 | .. code-block:: c |
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399 | |
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400 | rtems_status_code rtems_region_extend( |
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401 | rtems_id id, |
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402 | void *starting_address, |
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403 | uintptr_t length |
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404 | ); |
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405 | |
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406 | DIRECTIVE STATUS CODES: |
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407 | .. list-table:: |
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408 | :class: rtems-table |
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409 | |
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410 | * - ``RTEMS_SUCCESSFUL`` |
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411 | - region extended successfully |
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412 | * - ``RTEMS_INVALID_ADDRESS`` |
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413 | - ``starting_address`` is NULL |
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414 | * - ``RTEMS_INVALID_ID`` |
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415 | - invalid region id |
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416 | * - ``RTEMS_INVALID_ADDRESS`` |
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417 | - invalid address of area to add |
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418 | |
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419 | DESCRIPTION: |
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420 | This directive adds the memory area which starts at |
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421 | :c:data:`starting_address` for :c:data:`length` bytes to the region |
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422 | specified by :c:data:`id`. |
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423 | |
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424 | There are no alignment requirements for the memory area. The memory area |
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425 | must be big enough to contain some maintenance blocks. It must not overlap |
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426 | parts of the current heap memory areas. Disconnected memory areas added to |
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427 | the heap will lead to used blocks which cover the gaps. Extending with an |
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428 | inappropriate memory area will corrupt the heap resulting in undefined |
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429 | behaviour. |
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430 | |
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431 | NOTES: |
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432 | This directive will obtain the allocator mutex and may cause the calling |
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433 | task to be preempted. |
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434 | |
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435 | The calling task does not have to be the task that created the region. Any |
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436 | local task that knows the region identifier can extend the region. |
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437 | |
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438 | .. raw:: latex |
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439 | |
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440 | \clearpage |
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441 | |
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442 | .. index:: get segment from region |
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443 | .. index:: rtems_region_get_segment |
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444 | |
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445 | .. _rtems_region_get_segment: |
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446 | |
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447 | REGION_GET_SEGMENT - Get segment from a region |
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448 | ---------------------------------------------- |
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449 | |
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450 | CALLING SEQUENCE: |
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451 | .. code-block:: c |
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452 | |
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453 | rtems_status_code rtems_region_get_segment( |
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454 | rtems_id id, |
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455 | uintptr_t size, |
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456 | rtems_option option_set, |
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457 | rtems_interval timeout, |
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458 | void **segment |
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459 | ); |
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460 | |
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461 | DIRECTIVE STATUS CODES: |
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462 | .. list-table:: |
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463 | :class: rtems-table |
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464 | |
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465 | * - ``RTEMS_SUCCESSFUL`` |
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466 | - segment obtained successfully |
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467 | * - ``RTEMS_INVALID_ADDRESS`` |
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468 | - ``segment`` is NULL |
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469 | * - ``RTEMS_INVALID_ID`` |
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470 | - invalid region id |
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471 | * - ``RTEMS_INVALID_SIZE`` |
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472 | - request is for zero bytes or exceeds the size of maximum segment which is |
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473 | possible for this region |
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474 | * - ``RTEMS_UNSATISFIED`` |
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475 | - segment of requested size not available |
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476 | * - ``RTEMS_TIMEOUT`` |
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477 | - timed out waiting for segment |
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478 | * - ``RTEMS_OBJECT_WAS_DELETED`` |
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479 | - region deleted while waiting |
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480 | |
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481 | DESCRIPTION: |
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482 | This directive obtains a variable size segment from the region specified by |
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483 | ``id``. The address of the allocated segment is returned in segment. The |
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484 | ``RTEMS_WAIT`` and ``RTEMS_NO_WAIT`` components of the options parameter |
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485 | are used to specify whether the calling tasks wish to wait for a segment to |
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486 | become available or return immediately if no segment is available. For |
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487 | either option, if a sufficiently sized segment is available, then the |
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488 | segment is successfully acquired by returning immediately with the |
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489 | ``RTEMS_SUCCESSFUL`` status code. |
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490 | |
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491 | If the calling task chooses to return immediately and a segment large |
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492 | enough is not available, then an error code indicating this fact is |
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493 | returned. If the calling task chooses to wait for the segment and a |
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494 | segment large enough is not available, then the calling task is placed on |
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495 | the region's segment wait queue and blocked. If the region was created |
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496 | with the ``RTEMS_PRIORITY`` option, then the calling task is inserted into |
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497 | the wait queue according to its priority. However, if the region was |
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498 | created with the ``RTEMS_FIFO`` option, then the calling task is placed at |
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499 | the rear of the wait queue. |
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500 | |
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501 | The timeout parameter specifies the maximum interval that a task is willing |
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502 | to wait to obtain a segment. If timeout is set to ``RTEMS_NO_TIMEOUT``, |
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503 | then the calling task will wait forever. |
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504 | |
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505 | NOTES: |
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506 | This directive will obtain the allocator mutex and may cause the calling |
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507 | task to be preempted. |
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508 | |
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509 | The actual length of the allocated segment may be larger than the requested |
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510 | size because a segment size is always a multiple of the region's page size. |
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511 | |
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512 | The following segment acquisition option constants are defined by RTEMS: |
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513 | |
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514 | .. list-table:: |
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515 | :class: rtems-table |
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516 | |
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517 | * - ``RTEMS_WAIT`` |
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518 | - task will wait for segment (default) |
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519 | * - ``RTEMS_NO_WAIT`` |
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520 | - task should not wait |
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521 | |
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522 | A clock tick is required to support the timeout functionality of this |
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523 | directive. |
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524 | |
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525 | .. raw:: latex |
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526 | |
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527 | \clearpage |
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528 | |
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529 | .. index:: return segment to region |
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530 | .. index:: rtems_region_return_segment |
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531 | |
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532 | .. _rtems_region_return_segment: |
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533 | |
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534 | REGION_RETURN_SEGMENT - Return segment to a region |
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535 | -------------------------------------------------- |
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536 | |
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537 | CALLING SEQUENCE: |
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538 | .. code-block:: c |
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539 | |
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540 | rtems_status_code rtems_region_return_segment( |
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541 | rtems_id id, |
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542 | void *segment |
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543 | ); |
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544 | |
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545 | DIRECTIVE STATUS CODES: |
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546 | .. list-table:: |
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547 | :class: rtems-table |
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548 | |
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549 | * - ``RTEMS_SUCCESSFUL`` |
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550 | - segment returned successfully |
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551 | * - ``RTEMS_INVALID_ADDRESS`` |
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552 | - ``segment`` is NULL |
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553 | * - ``RTEMS_INVALID_ID`` |
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554 | - invalid region id |
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555 | * - ``RTEMS_INVALID_ADDRESS`` |
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556 | - segment address not in region |
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557 | |
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558 | DESCRIPTION: |
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559 | This directive returns the segment specified by segment to the region |
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560 | specified by id. The returned segment is merged with its neighbors to form |
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561 | the largest possible segment. The first task on the wait queue is examined |
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562 | to determine if its segment request can now be satisfied. If so, it is |
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563 | given a segment and unblocked. This process is repeated until the first |
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564 | task's segment request cannot be satisfied. |
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565 | |
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566 | NOTES: |
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567 | This directive will cause the calling task to be preempted if one or more |
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568 | local tasks are waiting for a segment and the following conditions exist: |
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569 | |
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570 | - a waiting task has a higher priority than the calling task |
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571 | |
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572 | - the size of the segment required by the waiting task is less than or |
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573 | equal to the size of the segment returned. |
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574 | |
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575 | .. raw:: latex |
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576 | |
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577 | \clearpage |
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578 | |
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579 | .. index:: get size of segment |
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580 | .. index:: rtems_region_get_segment_size |
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581 | |
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582 | .. _rtems_region_get_segment_size: |
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583 | |
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584 | REGION_GET_SEGMENT_SIZE - Obtain size of a segment |
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585 | -------------------------------------------------- |
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586 | |
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587 | CALLING SEQUENCE: |
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588 | .. code-block:: c |
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589 | |
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590 | rtems_status_code rtems_region_get_segment_size( |
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591 | rtems_id id, |
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592 | void *segment, |
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593 | uintptr_t *size |
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594 | ); |
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595 | |
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596 | DIRECTIVE STATUS CODES: |
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597 | .. list-table:: |
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598 | :class: rtems-table |
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599 | |
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600 | * - ``RTEMS_SUCCESSFUL`` |
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601 | - segment obtained successfully |
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602 | * - ``RTEMS_INVALID_ADDRESS`` |
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603 | - ``segment`` is NULL |
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604 | * - ``RTEMS_INVALID_ADDRESS`` |
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605 | - ``size`` is NULL |
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606 | * - ``RTEMS_INVALID_ID`` |
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607 | - invalid region id |
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608 | * - ``RTEMS_INVALID_ADDRESS`` |
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609 | - segment address not in region |
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610 | |
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611 | DESCRIPTION: |
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612 | This directive obtains the size in bytes of the specified segment. |
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613 | |
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614 | NOTES: |
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615 | The actual length of the allocated segment may be larger than the requested |
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616 | size because a segment size is always a multiple of the region's page size. |
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617 | |
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618 | .. raw:: latex |
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619 | |
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620 | \clearpage |
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621 | |
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622 | .. index:: resize segment |
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623 | .. index:: rtems_region_resize_segment |
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624 | |
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625 | .. _rtems_region_resize_segment: |
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626 | |
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627 | REGION_RESIZE_SEGMENT - Change size of a segment |
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628 | ------------------------------------------------ |
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629 | |
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630 | CALLING SEQUENCE: |
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631 | .. code-block:: c |
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632 | |
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633 | rtems_status_code rtems_region_resize_segment( |
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634 | rtems_id id, |
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635 | void *segment, |
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636 | uintptr_t new_size, |
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637 | uintptr_t *old_size |
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638 | ); |
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639 | |
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640 | DIRECTIVE STATUS CODES: |
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641 | .. list-table:: |
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642 | :class: rtems-table |
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643 | |
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644 | * - ``RTEMS_SUCCESSFUL`` |
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645 | - segment obtained successfully |
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646 | * - ``RTEMS_INVALID_ADDRESS`` |
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647 | - ``segment`` is NULL |
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648 | * - ``RTEMS_INVALID_ADDRESS`` |
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649 | - ``old_size`` is NULL |
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650 | * - ``RTEMS_INVALID_ID`` |
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651 | - invalid region id |
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652 | * - ``RTEMS_INVALID_ADDRESS`` |
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653 | - segment address not in region |
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654 | * - ``RTEMS_UNSATISFIED`` |
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655 | - unable to make segment larger |
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656 | |
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657 | DESCRIPTION: |
---|
658 | This directive is used to increase or decrease the size of a segment. When |
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659 | increasing the size of a segment, it is possible that there is not memory |
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660 | available contiguous to the segment. In this case, the request is |
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661 | unsatisfied. |
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662 | |
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663 | NOTES: |
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664 | This directive will obtain the allocator mutex and may cause the calling |
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665 | task to be preempted. |
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666 | |
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667 | If an attempt to increase the size of a segment fails, then the application |
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668 | may want to allocate a new segment of the desired size, copy the contents |
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669 | of the original segment to the new, larger segment and then return the |
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670 | original segment. |
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