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 129   <div class="headertitle"><div class="title">Technical Data and Limitations</div></div>
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 131 <div class="contents">
 132 <div class="textblock"><p><a class="anchor" id="md_src_2technical__data"></a></p>
 133 <p>This lists the technical data of CMSIS-FreeRTOS.</p>
 134 <h1><a class="anchor" id="autotoc_md10"></a>
 135 Limitations</h1>
 136 <p>The following list briefly describes the limitations and unsupported features of the CMSIS-RTOS2 wrapper for FreeRTOS:</p>
 137 <ul>
 138 <li>Static memory allocation will only work if <em>all</em> memory (from attributes structure) is provided statically. In order to allocate object memory statically, you need to:<ul>
 139 <li>provide the memory for control blocks and stack in the <code>osThreadAttr_t</code> structure for threads.</li>
 140 <li>provide the memory for control blocks and message data in the <code>osMessageQueueAttr_t</code> structure for memory queues.</li>
 141 <li>provide the memory for control blocks for other objects in the object's attributes structure.</li>
 142 </ul>
 143 </li>
 144 <li>Each timer object requires additional 8 bytes of memory:<ul>
 145 <li>to allocate all memory statically, provide the memory for control block of size (sizeof(StaticTimer_t) + 8 bytes)</li>
 146 <li>otherwise, additional 8 bytes of dynamic memory will be used</li>
 147 </ul>
 148 </li>
 149 <li><code>osKernelSuspend</code> and <code>osKernelResume</code> are not supported.</li>
 150 <li><code>osThreadDetach</code>, <code>osThreadJoin()</code> and attribute <code>osThreadJoinable</code> are not supported (<code>osThreadNew</code> returns NULL when <code>osThreadJoinable</code> attribute is specified).</li>
 151 <li><code>osThreadGetStackSize</code> is not implemented.</li>
 152 <li>Event flags are limited to 24 bits.</li>
 153 <li><code>osEventFlagsGetName</code> is not implemented.</li>
 154 <li><code>osEventFlagsWait</code> cannot be called from an ISR.</li>
 155 <li>Priority inherit protocol is used as default mutex behavior (<code>osMutexNew</code> creates priority inherit mutex object by default and ignores <code>osMutexPrioInherit</code> attribute when specified).</li>
 156 <li>Robust mutex objects are not supported (<code>osMutexNew</code> returns NULL when <code>osMutexRobust</code> attribute is specified).</li>
 157 <li><code>osMutexGetName</code> is not implemented and always returns NULL.</li>
 158 <li><code>osSemaphoreGetName</code> is not implemented and always returns NULL.</li>
 159 <li><code>osMessageQueueGetName</code> is not implemented and always returns NULL.</li>
 160 <li><code>osMessageQueuePut</code> and <code>osMessageQueueGet</code> always ignore message priority.</li>
 161 <li><em>Process Isolation (Functional Safety)</em> functions are not implemented.</li>
 162 </ul>
 163 <h1><a class="anchor" id="autotoc_md11"></a>
 164 Validation Suite Results</h1>
 165 <p>CMSIS provides a <a href="https://arm-software.github.io/CMSIS_6/latest/RTOS2/rtosValidation.html">CMSIS-RTOS2 validation suite</a> that can be used to test a real-time operating system for compliance to the standard. The test suite has been executed successfully on the CMSIS-FreeRTOS implementation (<a href="cmsis_rtos2_validation.txt">see results</a>).</p>
 166 <p>The following table explains the exceptions:</p>
 167 <table class="markdownTable">
 168 <tr class="markdownTableHead">
 169 <th class="markdownTableHeadNone">Test Case   </th><th class="markdownTableHeadNone">Result   </th><th class="markdownTableHeadNone">Reason   </th><th class="markdownTableHeadNone">Summary    </th></tr>
 170 <tr class="markdownTableRowOdd">
 171 <td class="markdownTableBodyNone">TC_osKernelGetState_2   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to call <code>osKernelGetState</code> after a <code>osKernelSuspend</code> call. <code>osKernelSuspend</code> is not implemented.    </td></tr>
 172 <tr class="markdownTableRowEven">
 173 <td class="markdownTableBodyNone">TC_osKernelLock_2   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to call <code>osKernelLock</code> after a <code>osKernelSuspend</code> call. <code>osKernelSuspend</code> is not implemented.    </td></tr>
 174 <tr class="markdownTableRowOdd">
 175 <td class="markdownTableBodyNone">TC_osKernelUnlock_2   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to call <code>osKernelUnlock</code> after a <code>osKernelSuspend</code> call. <code>osKernelSuspend</code> is not implemented.    </td></tr>
 176 <tr class="markdownTableRowEven">
 177 <td class="markdownTableBodyNone">TC_osKernelSuspend_1   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osKernelSuspend</code> which is not implemented.    </td></tr>
 178 <tr class="markdownTableRowOdd">
 179 <td class="markdownTableBodyNone">TC_osKernelResume_1   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osKernelResume</code> which is not implemented.    </td></tr>
 180 <tr class="markdownTableRowEven">
 181 <td class="markdownTableBodyNone">TC_osThreadNew_3   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to create joinable thread using <code>osThreadJoinable</code> attribute. FreeRTOS does not support joinable threads.    </td></tr>
 182 <tr class="markdownTableRowOdd">
 183 <td class="markdownTableBodyNone">TC_osThreadGetName_1   </td><td class="markdownTableBodyNone">failed   </td><td class="markdownTableBodyNone">deviation   </td><td class="markdownTableBodyNone">Test attempt to retrieve a name on an unnamed thread. An empty string is returned instead of NULL pointer.    </td></tr>
 184 <tr class="markdownTableRowEven">
 185 <td class="markdownTableBodyNone">TC_osThreadGetState_3   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to retrieve a state of a terminated joinable thread. FreeRTOS does not support joinable threads.    </td></tr>
 186 <tr class="markdownTableRowOdd">
 187 <td class="markdownTableBodyNone">TC_osThreadDetach_1   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osThreadDetach</code> which is not implemented.    </td></tr>
 188 <tr class="markdownTableRowEven">
 189 <td class="markdownTableBodyNone">TC_osThreadDetach_2   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osThreadDetach</code> which is not implemented.    </td></tr>
 190 <tr class="markdownTableRowOdd">
 191 <td class="markdownTableBodyNone">TC_osThreadJoin_1   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osThreadJoin</code> which is not implemented.    </td></tr>
 192 <tr class="markdownTableRowEven">
 193 <td class="markdownTableBodyNone">TC_osThreadJoin_2   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osThreadJoin</code> which is not implemented.    </td></tr>
 194 <tr class="markdownTableRowOdd">
 195 <td class="markdownTableBodyNone">TC_osThreadJoin_3   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osThreadJoin</code> which is not implemented.    </td></tr>
 196 <tr class="markdownTableRowEven">
 197 <td class="markdownTableBodyNone">TC_osThreadGetStackSize_1   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osThreadGetStackSize</code> which is not implemented.    </td></tr>
 198 <tr class="markdownTableRowOdd">
 199 <td class="markdownTableBodyNone">TC_ThreadReturn   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to terminate a thread by just returning from a thread. FreeRTOS threads may not return.    </td></tr>
 200 <tr class="markdownTableRowEven">
 201 <td class="markdownTableBodyNone">TC_osEventFlagsSet_1   </td><td class="markdownTableBodyNone">failed   </td><td class="markdownTableBodyNone">deviation   </td><td class="markdownTableBodyNone">Test attempts to set event flags by calling <code>osEventFlagsSet</code> multiple times without leaving ISR handler. To process ISR requests, FreeRTOS uses timer deamon which wakes-up after ISR execution.    </td></tr>
 202 <tr class="markdownTableRowOdd">
 203 <td class="markdownTableBodyNone">TC_osEventFlagsClear_1   </td><td class="markdownTableBodyNone">failed   </td><td class="markdownTableBodyNone">deviation   </td><td class="markdownTableBodyNone">Test attempts to clear event flags by calling <code>osEventFlagsClear</code> multiple times without leaving ISR handler. To process ISR requests, FreeRTOS uses timer deamon which wakes-up after ISR execution.    </td></tr>
 204 <tr class="markdownTableRowEven">
 205 <td class="markdownTableBodyNone">TC_osEventFlagsWait_1   </td><td class="markdownTableBodyNone">failed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to wait for flags from ISR with zero timeout (try-semantic). FreeRTOS does not support such operation.    </td></tr>
 206 <tr class="markdownTableRowOdd">
 207 <td class="markdownTableBodyNone">TC_osEventFlagsGetName_1   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osEventFlagsGetName</code> which is not implemented.    </td></tr>
 208 <tr class="markdownTableRowEven">
 209 <td class="markdownTableBodyNone">TC_osMutexNew_4   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to create a robust mutex. FreeRTOS implementation does not support robust mutexes.    </td></tr>
 210 <tr class="markdownTableRowOdd">
 211 <td class="markdownTableBodyNone">TC_osMutexGetName_1   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osMutexGetName</code> which is not implemented.    </td></tr>
 212 <tr class="markdownTableRowEven">
 213 <td class="markdownTableBodyNone">TC_MutexRobust   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to validate robust mutex behavior. FreeRTOS implementation does not support robust mutexes.    </td></tr>
 214 <tr class="markdownTableRowOdd">
 215 <td class="markdownTableBodyNone">TC_MutexOwnership   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test attempts to release a mutex from a thread which is not the mutex owner. FreeRTOS implementation does not verify ownership on mutex release.    </td></tr>
 216 <tr class="markdownTableRowEven">
 217 <td class="markdownTableBodyNone">TC_osSemaphoreGetName_1   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osSemaphoreGetName</code> which is not implemented.    </td></tr>
 218 <tr class="markdownTableRowOdd">
 219 <td class="markdownTableBodyNone">TC_osMessageQueueGetName_1   </td><td class="markdownTableBodyNone">not executed   </td><td class="markdownTableBodyNone">unsupported feature   </td><td class="markdownTableBodyNone">Test validates <code>osMessageQueueGetName</code> which is not implemented.   </td></tr>
 220 </table>
 221 <h1><a class="anchor" id="autotoc_md12"></a>
 222 Troubleshooting</h1>
 223 <p>Users looking for help shall check <a href="https://www.freertos.org/Why-FreeRTOS/FAQs">subsection of the full FreeRTOS FAQ</a>. It contains many useful information that also apply when using FreeRTOS in context of CMSIS-FreeRTOS.</p>
 224 <p>Additionally, please take a look at the following:</p>
 225 <ol type="1">
 226 <li><p class="startli"><b>Interrupts are disabled when main is called or before the kernel is started</b></p>
 227 <p class="startli">Before the FreeRTOS kernel is started, threads (i.e. tasks) may be created together with other objects like mutexes, semaphores, message queues etc. When functions like <code>xTaskCreate</code>, <code>xSemaphoreCreateMutex</code>, <code>xQueueCreate</code> and others get called, they prevent interrupt handlers from calling FreeRTOS API functions in order to keep FreeRTOS kernel variables and state machine consistent (see also here <a href="https://www.freertos.org/Why-FreeRTOS/FAQs">Interrupts are not executing</a>). In cases when interrupts may be executed after object creation and before the FreeRTOS kernel is started they can be re-enabled: </p><div class="fragment"><div class="line">portENABLE_INTERRUPTS();</div>
 228 </div><!-- fragment --><p> Make sure that the interrupts you execute in such case do not call FreeRTOS API. </p>
 229 </li>
 230 </ol>
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