2 FreeRTOS V7.3.0 - Copyright (C) 2012 Real Time Engineers Ltd.
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4 FEATURES AND PORTS ARE ADDED TO FREERTOS ALL THE TIME. PLEASE VISIT
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5 http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.
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7 ***************************************************************************
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9 * FreeRTOS tutorial books are available in pdf and paperback. *
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10 * Complete, revised, and edited pdf reference manuals are also *
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13 * Purchasing FreeRTOS documentation will not only help you, by *
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14 * ensuring you get running as quickly as possible and with an *
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15 * in-depth knowledge of how to use FreeRTOS, it will also help *
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16 * the FreeRTOS project to continue with its mission of providing *
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17 * professional grade, cross platform, de facto standard solutions *
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18 * for microcontrollers - completely free of charge! *
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20 * >>> See http://www.FreeRTOS.org/Documentation for details. <<< *
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22 * Thank you for using FreeRTOS, and thank you for your support! *
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24 ***************************************************************************
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27 This file is part of the FreeRTOS distribution.
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29 FreeRTOS is free software; you can redistribute it and/or modify it under
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30 the terms of the GNU General Public License (version 2) as published by the
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31 Free Software Foundation AND MODIFIED BY the FreeRTOS exception.
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32 >>>NOTE<<< The modification to the GPL is included to allow you to
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33 distribute a combined work that includes FreeRTOS without being obliged to
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34 provide the source code for proprietary components outside of the FreeRTOS
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35 kernel. FreeRTOS is distributed in the hope that it will be useful, but
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36 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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37 or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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38 more details. You should have received a copy of the GNU General Public
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39 License and the FreeRTOS license exception along with FreeRTOS; if not it
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40 can be viewed here: http://www.freertos.org/a00114.html and also obtained
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41 by writing to Richard Barry, contact details for whom are available on the
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46 ***************************************************************************
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48 * Having a problem? Start by reading the FAQ "My application does *
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49 * not run, what could be wrong?" *
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51 * http://www.FreeRTOS.org/FAQHelp.html *
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53 ***************************************************************************
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56 http://www.FreeRTOS.org - Documentation, training, latest versions, license
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57 and contact details.
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59 http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
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60 including FreeRTOS+Trace - an indispensable productivity tool.
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62 Real Time Engineers ltd license FreeRTOS to High Integrity Systems, who sell
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63 the code with commercial support, indemnification, and middleware, under
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64 the OpenRTOS brand: http://www.OpenRTOS.com. High Integrity Systems also
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65 provide a safety engineered and independently SIL3 certified version under
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66 the SafeRTOS brand: http://www.SafeRTOS.com.
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70 The tasks defined on this page demonstrate the use of recursive mutexes.
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72 For recursive mutex functionality the created mutex should be created using
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73 xSemaphoreCreateRecursiveMutex(), then be manipulated
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74 using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
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77 This demo creates three tasks all of which access the same recursive mutex:
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79 prvRecursiveMutexControllingTask() has the highest priority so executes
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80 first and grabs the mutex. It then performs some recursive accesses -
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81 between each of which it sleeps for a short period to let the lower
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82 priority tasks execute. When it has completed its demo functionality
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83 it gives the mutex back before suspending itself.
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85 prvRecursiveMutexBlockingTask() attempts to access the mutex by performing
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86 a blocking 'take'. The blocking task has a lower priority than the
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87 controlling task so by the time it executes the mutex has already been
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88 taken by the controlling task, causing the blocking task to block. It
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89 does not unblock until the controlling task has given the mutex back,
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90 and it does not actually run until the controlling task has suspended
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91 itself (due to the relative priorities). When it eventually does obtain
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92 the mutex all it does is give the mutex back prior to also suspending
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93 itself. At this point both the controlling task and the blocking task are
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96 prvRecursiveMutexPollingTask() runs at the idle priority. It spins round
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97 a tight loop attempting to obtain the mutex with a non-blocking call. As
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98 the lowest priority task it will not successfully obtain the mutex until
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99 both the controlling and blocking tasks are suspended. Once it eventually
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100 does obtain the mutex it first unsuspends both the controlling task and
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101 blocking task prior to giving the mutex back - resulting in the polling
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102 task temporarily inheriting the controlling tasks priority.
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105 /* Scheduler include files. */
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106 #include "FreeRTOS.h"
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108 #include "semphr.h"
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110 /* Demo app include files. */
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111 #include "recmutex.h"
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113 /* Priorities assigned to the three tasks. */
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114 #define recmuCONTROLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 2 )
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115 #define recmuBLOCKING_TASK_PRIORITY ( tskIDLE_PRIORITY + 1 )
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116 #define recmuPOLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 0 )
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118 /* In this version the tick period is very long, so the short delay cannot be
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119 for too many ticks, or the check task will execute and find that the recmutex
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120 tasks have not completed their functionality and then signal an error. The
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121 delay does however have to be long enough to allow the lower priority tasks
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122 a chance of executing - this is basically achieved by reducing the number
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123 of times the loop that takes/gives the recursive mutex executes. */
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124 #define recmuMAX_COUNT ( 2 )
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125 #define recmuSHORT_DELAY ( 20 )
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126 #define recmuNO_DELAY ( ( portTickType ) 0 )
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127 #define recmuFIVE_TICK_DELAY ( ( portTickType ) 5 )
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129 /* The three tasks as described at the top of this file. */
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130 static void prvRecursiveMutexControllingTask( void *pvParameters );
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131 static void prvRecursiveMutexBlockingTask( void *pvParameters );
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132 static void prvRecursiveMutexPollingTask( void *pvParameters );
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134 /* The mutex used by the demo. */
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135 static xSemaphoreHandle xMutex;
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137 /* Variables used to detect and latch errors. */
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138 static volatile portBASE_TYPE xErrorOccurred = pdFALSE, xControllingIsSuspended = pdFALSE, xBlockingIsSuspended = pdFALSE;
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139 static volatile unsigned portBASE_TYPE uxControllingCycles = 0, uxBlockingCycles = 0, uxPollingCycles = 0;
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141 /* Handles of the two higher priority tasks, required so they can be resumed
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143 static xTaskHandle xControllingTaskHandle, xBlockingTaskHandle;
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145 /*-----------------------------------------------------------*/
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147 void vStartRecursiveMutexTasks( void )
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149 /* Just creates the mutex and the three tasks. */
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151 xMutex = xSemaphoreCreateRecursiveMutex();
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153 /* vQueueAddToRegistry() adds the mutex to the registry, if one is
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154 in use. The registry is provided as a means for kernel aware
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155 debuggers to locate mutex and has no purpose if a kernel aware debugger
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156 is not being used. The call to vQueueAddToRegistry() will be removed
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157 by the pre-processor if configQUEUE_REGISTRY_SIZE is not defined or is
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158 defined to be less than 1. */
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159 vQueueAddToRegistry( ( xQueueHandle ) xMutex, ( signed portCHAR * ) "Recursive_Mutex" );
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162 if( xMutex != NULL )
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164 xTaskCreate( prvRecursiveMutexControllingTask, ( signed portCHAR * ) "Rec1Ctrl", configMINIMAL_STACK_SIZE, NULL, recmuCONTROLLING_TASK_PRIORITY, &xControllingTaskHandle );
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165 xTaskCreate( prvRecursiveMutexBlockingTask, ( signed portCHAR * ) "Rec2Blck", configMINIMAL_STACK_SIZE, NULL, recmuBLOCKING_TASK_PRIORITY, &xBlockingTaskHandle );
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166 xTaskCreate( prvRecursiveMutexPollingTask, ( signed portCHAR * ) "Rec3Poll", configMINIMAL_STACK_SIZE, NULL, recmuPOLLING_TASK_PRIORITY, NULL );
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169 /*-----------------------------------------------------------*/
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171 static void prvRecursiveMutexControllingTask( void *pvParameters )
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173 unsigned portBASE_TYPE ux;
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175 /* Just to remove compiler warning. */
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176 ( void ) pvParameters;
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180 /* Should not be able to 'give' the mutex, as we have not yet 'taken'
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181 it. The first time through, the mutex will not have been used yet,
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182 subsequent times through, at this point the mutex will be held by the
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184 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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186 xErrorOccurred = pdTRUE;
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189 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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191 /* We should now be able to take the mutex as many times as
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194 The first time through the mutex will be immediately available, on
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195 subsequent times through the mutex will be held by the polling task
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196 at this point and this Take will cause the polling task to inherit
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197 the priority of this task. In this case the block time must be
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198 long enough to ensure the polling task will execute again before the
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199 block time expires. If the block time does expire then the error
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200 flag will be set here. */
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201 if( xSemaphoreTakeRecursive( xMutex, recmuFIVE_TICK_DELAY ) != pdPASS )
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203 xErrorOccurred = pdTRUE;
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206 /* Ensure the other task attempting to access the mutex (and the
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207 other demo tasks) are able to execute to ensure they either block
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208 (where a block time is specified) or return an error (where no
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209 block time is specified) as the mutex is held by this task. */
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210 vTaskDelay( recmuSHORT_DELAY );
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213 /* For each time we took the mutex, give it back. */
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214 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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216 /* Ensure the other task attempting to access the mutex (and the
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217 other demo tasks) are able to execute. */
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218 vTaskDelay( recmuSHORT_DELAY );
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220 /* We should now be able to give the mutex as many times as we
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221 took it. When the mutex is available again the Blocking task
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222 should be unblocked but not run because it has a lower priority
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223 than this task. The polling task should also not run at this point
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224 as it too has a lower priority than this task. */
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225 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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227 xErrorOccurred = pdTRUE;
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231 /* Having given it back the same number of times as it was taken, we
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232 should no longer be the mutex owner, so the next give should fail. */
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233 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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235 xErrorOccurred = pdTRUE;
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238 /* Keep count of the number of cycles this task has performed so a
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239 stall can be detected. */
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240 uxControllingCycles++;
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242 /* Suspend ourselves so the blocking task can execute. */
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243 xControllingIsSuspended = pdTRUE;
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244 vTaskSuspend( NULL );
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245 xControllingIsSuspended = pdFALSE;
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248 /*-----------------------------------------------------------*/
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250 static void prvRecursiveMutexBlockingTask( void *pvParameters )
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252 /* Just to remove compiler warning. */
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253 ( void ) pvParameters;
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257 /* This task will run while the controlling task is blocked, and the
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258 controlling task will block only once it has the mutex - therefore
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259 this call should block until the controlling task has given up the
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260 mutex, and not actually execute past this call until the controlling
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261 task is suspended. */
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262 if( xSemaphoreTakeRecursive( xMutex, portMAX_DELAY ) == pdPASS )
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264 if( xControllingIsSuspended != pdTRUE )
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266 /* Did not expect to execute until the controlling task was
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268 xErrorOccurred = pdTRUE;
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272 /* Give the mutex back before suspending ourselves to allow
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273 the polling task to obtain the mutex. */
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274 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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276 xErrorOccurred = pdTRUE;
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279 xBlockingIsSuspended = pdTRUE;
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280 vTaskSuspend( NULL );
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281 xBlockingIsSuspended = pdFALSE;
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286 /* We should not leave the xSemaphoreTakeRecursive() function
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287 until the mutex was obtained. */
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288 xErrorOccurred = pdTRUE;
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291 /* The controlling and blocking tasks should be in lock step. */
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292 if( uxControllingCycles != ( uxBlockingCycles + 1 ) )
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294 xErrorOccurred = pdTRUE;
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297 /* Keep count of the number of cycles this task has performed so a
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298 stall can be detected. */
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299 uxBlockingCycles++;
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302 /*-----------------------------------------------------------*/
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304 static void prvRecursiveMutexPollingTask( void *pvParameters )
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306 /* Just to remove compiler warning. */
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307 ( void ) pvParameters;
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311 /* Keep attempting to obtain the mutex. We should only obtain it when
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312 the blocking task has suspended itself, which in turn should only
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313 happen when the controlling task is also suspended. */
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314 if( xSemaphoreTakeRecursive( xMutex, recmuNO_DELAY ) == pdPASS )
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316 /* Is the blocking task suspended? */
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317 if( ( xBlockingIsSuspended != pdTRUE ) || ( xControllingIsSuspended != pdTRUE ) )
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319 xErrorOccurred = pdTRUE;
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323 /* Keep count of the number of cycles this task has performed
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324 so a stall can be detected. */
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327 /* We can resume the other tasks here even though they have a
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328 higher priority than the polling task. When they execute they
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329 will attempt to obtain the mutex but fail because the polling
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330 task is still the mutex holder. The polling task (this task)
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331 will then inherit the higher priority. The Blocking task will
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332 block indefinitely when it attempts to obtain the mutex, the
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333 Controlling task will only block for a fixed period and an
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334 error will be latched if the polling task has not returned the
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335 mutex by the time this fixed period has expired. */
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336 vTaskResume( xBlockingTaskHandle );
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337 vTaskResume( xControllingTaskHandle );
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339 /* The other two tasks should now have executed and no longer
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341 if( ( xBlockingIsSuspended == pdTRUE ) || ( xControllingIsSuspended == pdTRUE ) )
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343 xErrorOccurred = pdTRUE;
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346 /* Release the mutex, disinheriting the higher priority again. */
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347 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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349 xErrorOccurred = pdTRUE;
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354 #if configUSE_PREEMPTION == 0
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361 /*-----------------------------------------------------------*/
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363 /* This is called to check that all the created tasks are still running. */
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364 portBASE_TYPE xAreRecursiveMutexTasksStillRunning( void )
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366 portBASE_TYPE xReturn;
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367 static unsigned portBASE_TYPE uxLastControllingCycles = 0, uxLastBlockingCycles = 0, uxLastPollingCycles = 0;
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369 /* Is the controlling task still cycling? */
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370 if( uxLastControllingCycles == uxControllingCycles )
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372 xErrorOccurred = pdTRUE;
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376 uxLastControllingCycles = uxControllingCycles;
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379 /* Is the blocking task still cycling? */
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380 if( uxLastBlockingCycles == uxBlockingCycles )
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382 xErrorOccurred = pdTRUE;
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386 uxLastBlockingCycles = uxBlockingCycles;
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389 /* Is the polling task still cycling? */
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390 if( uxLastPollingCycles == uxPollingCycles )
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392 xErrorOccurred = pdTRUE;
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396 uxLastPollingCycles = uxPollingCycles;
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399 if( xErrorOccurred == pdTRUE )
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projects / freertos / blob