2 FreeRTOS V6.1.1 - Copyright (C) 2011 Real Time Engineers Ltd.
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4 ***************************************************************************
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8 * + New to FreeRTOS, *
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11 * + Wanting to improve your FreeRTOS skills and productivity *
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13 * then take a look at the FreeRTOS books - available as PDF or paperback *
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15 * "Using the FreeRTOS Real Time Kernel - a Practical Guide" *
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16 * http://www.FreeRTOS.org/Documentation *
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18 * A pdf reference manual is also available. Both are usually delivered *
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19 * to your inbox within 20 minutes to two hours when purchased between 8am *
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20 * and 8pm GMT (although please allow up to 24 hours in case of *
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21 * exceptional circumstances). Thank you for your support! *
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23 ***************************************************************************
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25 This file is part of the FreeRTOS distribution.
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27 FreeRTOS is free software; you can redistribute it and/or modify it under
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28 the terms of the GNU General Public License (version 2) as published by the
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29 Free Software Foundation AND MODIFIED BY the FreeRTOS exception.
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30 ***NOTE*** The exception to the GPL is included to allow you to distribute
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31 a combined work that includes FreeRTOS without being obliged to provide the
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32 source code for proprietary components outside of the FreeRTOS kernel.
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33 FreeRTOS is distributed in the hope that it will be useful, but WITHOUT
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34 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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35 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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36 more details. You should have received a copy of the GNU General Public
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37 License and the FreeRTOS license exception along with FreeRTOS; if not it
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38 can be viewed here: http://www.freertos.org/a00114.html and also obtained
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39 by writing to Richard Barry, contact details for whom are available on the
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44 http://www.FreeRTOS.org - Documentation, latest information, license and
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47 http://www.SafeRTOS.com - A version that is certified for use in safety
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50 http://www.OpenRTOS.com - Commercial support, development, porting,
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51 licensing and training services.
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55 The tasks defined on this page demonstrate the use of recursive mutexes.
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57 For recursive mutex functionality the created mutex should be created using
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58 xSemaphoreCreateRecursiveMutex(), then be manipulated
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59 using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
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62 This demo creates three tasks all of which access the same recursive mutex:
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64 prvRecursiveMutexControllingTask() has the highest priority so executes
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65 first and grabs the mutex. It then performs some recursive accesses -
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66 between each of which it sleeps for a short period to let the lower
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67 priority tasks execute. When it has completed its demo functionality
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68 it gives the mutex back before suspending itself.
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70 prvRecursiveMutexBlockingTask() attempts to access the mutex by performing
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71 a blocking 'take'. The blocking task has a lower priority than the
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72 controlling task so by the time it executes the mutex has already been
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73 taken by the controlling task, causing the blocking task to block. It
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74 does not unblock until the controlling task has given the mutex back,
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75 and it does not actually run until the controlling task has suspended
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76 itself (due to the relative priorities). When it eventually does obtain
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77 the mutex all it does is give the mutex back prior to also suspending
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78 itself. At this point both the controlling task and the blocking task are
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81 prvRecursiveMutexPollingTask() runs at the idle priority. It spins round
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82 a tight loop attempting to obtain the mutex with a non-blocking call. As
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83 the lowest priority task it will not successfully obtain the mutex until
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84 both the controlling and blocking tasks are suspended. Once it eventually
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85 does obtain the mutex it first unsuspends both the controlling task and
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86 blocking task prior to giving the mutex back - resulting in the polling
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87 task temporarily inheriting the controlling tasks priority.
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90 /* Scheduler include files. */
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91 #include "FreeRTOS.h"
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95 /* Demo app include files. */
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96 #include "recmutex.h"
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98 /* Priorities assigned to the three tasks. */
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99 #define recmuCONTROLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 2 )
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100 #define recmuBLOCKING_TASK_PRIORITY ( tskIDLE_PRIORITY + 1 )
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101 #define recmuPOLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 0 )
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103 /* In this version the tick period is very long, so the short delay cannot be
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104 for too many ticks, or the check task will execute and find that the recmutex
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105 tasks have not completed their functionality and then signal an error. The
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106 delay does however have to be long enough to allow the lower priority tasks
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107 a chance of executing - this is basically achieved by reducing the number
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108 of times the loop that takes/gives the recursive mutex executes. */
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109 #define recmuMAX_COUNT ( 2 )
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110 #define recmuSHORT_DELAY ( 20 )
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111 #define recmuNO_DELAY ( ( portTickType ) 0 )
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112 #define recmuFIVE_TICK_DELAY ( ( portTickType ) 5 )
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114 /* The three tasks as described at the top of this file. */
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115 static void prvRecursiveMutexControllingTask( void *pvParameters );
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116 static void prvRecursiveMutexBlockingTask( void *pvParameters );
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117 static void prvRecursiveMutexPollingTask( void *pvParameters );
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119 /* The mutex used by the demo. */
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120 static xSemaphoreHandle xMutex;
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122 /* Variables used to detect and latch errors. */
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123 static volatile portBASE_TYPE xErrorOccurred = pdFALSE, xControllingIsSuspended = pdFALSE, xBlockingIsSuspended = pdFALSE;
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124 static volatile unsigned portBASE_TYPE uxControllingCycles = 0, uxBlockingCycles = 0, uxPollingCycles = 0;
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126 /* Handles of the two higher priority tasks, required so they can be resumed
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128 static xTaskHandle xControllingTaskHandle, xBlockingTaskHandle;
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130 /*-----------------------------------------------------------*/
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132 void vStartRecursiveMutexTasks( void )
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134 /* Just creates the mutex and the three tasks. */
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136 xMutex = xSemaphoreCreateRecursiveMutex();
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138 /* vQueueAddToRegistry() adds the mutex to the registry, if one is
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139 in use. The registry is provided as a means for kernel aware
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140 debuggers to locate mutex and has no purpose if a kernel aware debugger
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141 is not being used. The call to vQueueAddToRegistry() will be removed
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142 by the pre-processor if configQUEUE_REGISTRY_SIZE is not defined or is
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143 defined to be less than 1. */
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144 vQueueAddToRegistry( ( xQueueHandle ) xMutex, ( signed portCHAR * ) "Recursive_Mutex" );
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147 if( xMutex != NULL )
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149 xTaskCreate( prvRecursiveMutexControllingTask, ( signed portCHAR * ) "Rec1Ctrl", configMINIMAL_STACK_SIZE, NULL, recmuCONTROLLING_TASK_PRIORITY, &xControllingTaskHandle );
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150 xTaskCreate( prvRecursiveMutexBlockingTask, ( signed portCHAR * ) "Rec2Blck", configMINIMAL_STACK_SIZE, NULL, recmuBLOCKING_TASK_PRIORITY, &xBlockingTaskHandle );
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151 xTaskCreate( prvRecursiveMutexPollingTask, ( signed portCHAR * ) "Rec3Poll", configMINIMAL_STACK_SIZE, NULL, recmuPOLLING_TASK_PRIORITY, NULL );
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154 /*-----------------------------------------------------------*/
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156 static void prvRecursiveMutexControllingTask( void *pvParameters )
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158 unsigned portBASE_TYPE ux;
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160 /* Just to remove compiler warning. */
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161 ( void ) pvParameters;
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165 /* Should not be able to 'give' the mutex, as we have not yet 'taken'
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166 it. The first time through, the mutex will not have been used yet,
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167 subsequent times through, at this point the mutex will be held by the
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169 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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171 xErrorOccurred = pdTRUE;
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174 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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176 /* We should now be able to take the mutex as many times as
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179 The first time through the mutex will be immediately available, on
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180 subsequent times through the mutex will be held by the polling task
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181 at this point and this Take will cause the polling task to inherit
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182 the priority of this task. In this case the block time must be
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183 long enough to ensure the polling task will execute again before the
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184 block time expires. If the block time does expire then the error
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185 flag will be set here. */
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186 if( xSemaphoreTakeRecursive( xMutex, recmuFIVE_TICK_DELAY ) != pdPASS )
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188 xErrorOccurred = pdTRUE;
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191 /* Ensure the other task attempting to access the mutex (and the
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192 other demo tasks) are able to execute to ensure they either block
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193 (where a block time is specified) or return an error (where no
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194 block time is specified) as the mutex is held by this task. */
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195 vTaskDelay( recmuSHORT_DELAY );
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198 /* For each time we took the mutex, give it back. */
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199 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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201 /* Ensure the other task attempting to access the mutex (and the
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202 other demo tasks) are able to execute. */
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203 vTaskDelay( recmuSHORT_DELAY );
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205 /* We should now be able to give the mutex as many times as we
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206 took it. When the mutex is available again the Blocking task
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207 should be unblocked but not run because it has a lower priority
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208 than this task. The polling task should also not run at this point
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209 as it too has a lower priority than this task. */
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210 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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212 xErrorOccurred = pdTRUE;
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216 /* Having given it back the same number of times as it was taken, we
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217 should no longer be the mutex owner, so the next give should fail. */
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218 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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220 xErrorOccurred = pdTRUE;
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223 /* Keep count of the number of cycles this task has performed so a
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224 stall can be detected. */
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225 uxControllingCycles++;
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227 /* Suspend ourselves so the blocking task can execute. */
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228 xControllingIsSuspended = pdTRUE;
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229 vTaskSuspend( NULL );
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230 xControllingIsSuspended = pdFALSE;
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233 /*-----------------------------------------------------------*/
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235 static void prvRecursiveMutexBlockingTask( void *pvParameters )
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237 /* Just to remove compiler warning. */
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238 ( void ) pvParameters;
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242 /* This task will run while the controlling task is blocked, and the
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243 controlling task will block only once it has the mutex - therefore
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244 this call should block until the controlling task has given up the
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245 mutex, and not actually execute past this call until the controlling
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246 task is suspended. */
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247 if( xSemaphoreTakeRecursive( xMutex, portMAX_DELAY ) == pdPASS )
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249 if( xControllingIsSuspended != pdTRUE )
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251 /* Did not expect to execute until the controlling task was
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253 xErrorOccurred = pdTRUE;
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257 /* Give the mutex back before suspending ourselves to allow
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258 the polling task to obtain the mutex. */
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259 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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261 xErrorOccurred = pdTRUE;
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264 xBlockingIsSuspended = pdTRUE;
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265 vTaskSuspend( NULL );
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266 xBlockingIsSuspended = pdFALSE;
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271 /* We should not leave the xSemaphoreTakeRecursive() function
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272 until the mutex was obtained. */
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273 xErrorOccurred = pdTRUE;
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276 /* The controlling and blocking tasks should be in lock step. */
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277 if( uxControllingCycles != ( uxBlockingCycles + 1 ) )
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279 xErrorOccurred = pdTRUE;
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282 /* Keep count of the number of cycles this task has performed so a
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283 stall can be detected. */
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284 uxBlockingCycles++;
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287 /*-----------------------------------------------------------*/
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289 static void prvRecursiveMutexPollingTask( void *pvParameters )
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291 /* Just to remove compiler warning. */
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292 ( void ) pvParameters;
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296 /* Keep attempting to obtain the mutex. We should only obtain it when
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297 the blocking task has suspended itself, which in turn should only
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298 happen when the controlling task is also suspended. */
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299 if( xSemaphoreTakeRecursive( xMutex, recmuNO_DELAY ) == pdPASS )
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301 /* Is the blocking task suspended? */
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302 if( ( xBlockingIsSuspended != pdTRUE ) || ( xControllingIsSuspended != pdTRUE ) )
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304 xErrorOccurred = pdTRUE;
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308 /* Keep count of the number of cycles this task has performed
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309 so a stall can be detected. */
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312 /* We can resume the other tasks here even though they have a
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313 higher priority than the polling task. When they execute they
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314 will attempt to obtain the mutex but fail because the polling
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315 task is still the mutex holder. The polling task (this task)
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316 will then inherit the higher priority. The Blocking task will
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317 block indefinitely when it attempts to obtain the mutex, the
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318 Controlling task will only block for a fixed period and an
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319 error will be latched if the polling task has not returned the
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320 mutex by the time this fixed period has expired. */
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321 vTaskResume( xBlockingTaskHandle );
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322 vTaskResume( xControllingTaskHandle );
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324 /* The other two tasks should now have executed and no longer
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326 if( ( xBlockingIsSuspended == pdTRUE ) || ( xControllingIsSuspended == pdTRUE ) )
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328 xErrorOccurred = pdTRUE;
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331 /* Release the mutex, disinheriting the higher priority again. */
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332 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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334 xErrorOccurred = pdTRUE;
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339 #if configUSE_PREEMPTION == 0
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346 /*-----------------------------------------------------------*/
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348 /* This is called to check that all the created tasks are still running. */
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349 portBASE_TYPE xAreRecursiveMutexTasksStillRunning( void )
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351 portBASE_TYPE xReturn;
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352 static unsigned portBASE_TYPE uxLastControllingCycles = 0, uxLastBlockingCycles = 0, uxLastPollingCycles = 0;
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354 /* Is the controlling task still cycling? */
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355 if( uxLastControllingCycles == uxControllingCycles )
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357 xErrorOccurred = pdTRUE;
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361 uxLastControllingCycles = uxControllingCycles;
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364 /* Is the blocking task still cycling? */
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365 if( uxLastBlockingCycles == uxBlockingCycles )
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367 xErrorOccurred = pdTRUE;
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371 uxLastBlockingCycles = uxBlockingCycles;
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374 /* Is the polling task still cycling? */
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375 if( uxLastPollingCycles == uxPollingCycles )
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377 xErrorOccurred = pdTRUE;
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381 uxLastPollingCycles = uxPollingCycles;
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384 if( xErrorOccurred == pdTRUE )
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