2 FreeRTOS V7.4.1 - Copyright (C) 2013 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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33 >>>>>>NOTE<<<<<< The modification to the GPL is included to allow you to
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34 distribute a combined work that includes FreeRTOS without being obliged to
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35 provide the source code for proprietary components outside of the FreeRTOS
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38 FreeRTOS is distributed in the hope that it will be useful, but WITHOUT ANY
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39 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
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40 FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
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41 details. You should have received a copy of the GNU General Public License
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42 and the FreeRTOS license exception along with FreeRTOS; if not it can be
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43 viewed here: http://www.freertos.org/a00114.html and also obtained by
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44 writing to Real Time Engineers Ltd., contact details for whom are available
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45 on the FreeRTOS WEB site.
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49 ***************************************************************************
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51 * Having a problem? Start by reading the FAQ "My application does *
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52 * not run, what could be wrong?" *
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54 * http://www.FreeRTOS.org/FAQHelp.html *
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56 ***************************************************************************
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59 http://www.FreeRTOS.org - Documentation, books, training, latest versions,
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60 license and Real Time Engineers Ltd. contact details.
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62 http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
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63 including FreeRTOS+Trace - an indispensable productivity tool, and our new
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64 fully thread aware and reentrant UDP/IP stack.
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66 http://www.OpenRTOS.com - Real Time Engineers ltd license FreeRTOS to High
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67 Integrity Systems, who sell the code with commercial support,
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68 indemnification and middleware, under the OpenRTOS brand.
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70 http://www.SafeRTOS.com - High Integrity Systems also provide a safety
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71 engineered and independently SIL3 certified version for use in safety and
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72 mission critical applications that require provable dependability.
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76 The tasks defined on this page demonstrate the use of recursive mutexes.
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78 For recursive mutex functionality the created mutex should be created using
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79 xSemaphoreCreateRecursiveMutex(), then be manipulated
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80 using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
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83 This demo creates three tasks all of which access the same recursive mutex:
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85 prvRecursiveMutexControllingTask() has the highest priority so executes
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86 first and grabs the mutex. It then performs some recursive accesses -
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87 between each of which it sleeps for a short period to let the lower
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88 priority tasks execute. When it has completed its demo functionality
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89 it gives the mutex back before suspending itself.
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91 prvRecursiveMutexBlockingTask() attempts to access the mutex by performing
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92 a blocking 'take'. The blocking task has a lower priority than the
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93 controlling task so by the time it executes the mutex has already been
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94 taken by the controlling task, causing the blocking task to block. It
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95 does not unblock until the controlling task has given the mutex back,
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96 and it does not actually run until the controlling task has suspended
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97 itself (due to the relative priorities). When it eventually does obtain
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98 the mutex all it does is give the mutex back prior to also suspending
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99 itself. At this point both the controlling task and the blocking task are
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102 prvRecursiveMutexPollingTask() runs at the idle priority. It spins round
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103 a tight loop attempting to obtain the mutex with a non-blocking call. As
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104 the lowest priority task it will not successfully obtain the mutex until
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105 both the controlling and blocking tasks are suspended. Once it eventually
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106 does obtain the mutex it first unsuspends both the controlling task and
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107 blocking task prior to giving the mutex back - resulting in the polling
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108 task temporarily inheriting the controlling tasks priority.
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111 /* Scheduler include files. */
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112 #include "FreeRTOS.h"
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114 #include "semphr.h"
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116 /* Demo app include files. */
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117 #include "recmutex.h"
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119 /* Priorities assigned to the three tasks. */
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120 #define recmuCONTROLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 2 )
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121 #define recmuBLOCKING_TASK_PRIORITY ( tskIDLE_PRIORITY + 1 )
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122 #define recmuPOLLING_TASK_PRIORITY ( tskIDLE_PRIORITY + 0 )
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124 /* The recursive call depth. */
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125 #define recmuMAX_COUNT ( 10 )
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128 #define recmuSHORT_DELAY ( 20 / portTICK_RATE_MS )
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129 #define recmuNO_DELAY ( ( portTickType ) 0 )
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130 #define recmuTWO_TICK_DELAY ( ( portTickType ) 2 )
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132 /* The three tasks as described at the top of this file. */
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133 static void prvRecursiveMutexControllingTask( void *pvParameters );
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134 static void prvRecursiveMutexBlockingTask( void *pvParameters );
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135 static void prvRecursiveMutexPollingTask( void *pvParameters );
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137 /* The mutex used by the demo. */
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138 static xSemaphoreHandle xMutex;
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140 /* Variables used to detect and latch errors. */
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141 static volatile portBASE_TYPE xErrorOccurred = pdFALSE, xControllingIsSuspended = pdFALSE, xBlockingIsSuspended = pdFALSE;
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142 static volatile unsigned portBASE_TYPE uxControllingCycles = 0, uxBlockingCycles = 0, uxPollingCycles = 0;
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144 /* Handles of the two higher priority tasks, required so they can be resumed
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146 static xTaskHandle xControllingTaskHandle, xBlockingTaskHandle;
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148 /*-----------------------------------------------------------*/
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150 void vStartRecursiveMutexTasks( void )
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152 /* Just creates the mutex and the three tasks. */
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154 xMutex = xSemaphoreCreateRecursiveMutex();
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156 /* vQueueAddToRegistry() adds the mutex to the registry, if one is
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157 in use. The registry is provided as a means for kernel aware
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158 debuggers to locate mutex and has no purpose if a kernel aware debugger
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159 is not being used. The call to vQueueAddToRegistry() will be removed
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160 by the pre-processor if configQUEUE_REGISTRY_SIZE is not defined or is
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161 defined to be less than 1. */
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162 vQueueAddToRegistry( ( xQueueHandle ) xMutex, ( signed portCHAR * ) "Recursive_Mutex" );
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165 if( xMutex != NULL )
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167 xTaskCreate( prvRecursiveMutexControllingTask, ( signed portCHAR * ) "Rec1", configMINIMAL_STACK_SIZE, NULL, recmuCONTROLLING_TASK_PRIORITY, &xControllingTaskHandle );
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168 xTaskCreate( prvRecursiveMutexBlockingTask, ( signed portCHAR * ) "Rec2", configMINIMAL_STACK_SIZE, NULL, recmuBLOCKING_TASK_PRIORITY, &xBlockingTaskHandle );
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169 xTaskCreate( prvRecursiveMutexPollingTask, ( signed portCHAR * ) "Rec3", configMINIMAL_STACK_SIZE, NULL, recmuPOLLING_TASK_PRIORITY, NULL );
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172 /*-----------------------------------------------------------*/
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174 static void prvRecursiveMutexControllingTask( void *pvParameters )
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176 unsigned portBASE_TYPE ux;
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178 /* Just to remove compiler warning. */
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179 ( void ) pvParameters;
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183 /* Should not be able to 'give' the mutex, as we have not yet 'taken'
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184 it. The first time through, the mutex will not have been used yet,
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185 subsequent times through, at this point the mutex will be held by the
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187 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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189 xErrorOccurred = pdTRUE;
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192 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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194 /* We should now be able to take the mutex as many times as
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197 The first time through the mutex will be immediately available, on
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198 subsequent times through the mutex will be held by the polling task
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199 at this point and this Take will cause the polling task to inherit
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200 the priority of this task. In this case the block time must be
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201 long enough to ensure the polling task will execute again before the
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202 block time expires. If the block time does expire then the error
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203 flag will be set here. */
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204 if( xSemaphoreTakeRecursive( xMutex, recmuTWO_TICK_DELAY ) != pdPASS )
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206 xErrorOccurred = pdTRUE;
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209 /* Ensure the other task attempting to access the mutex (and the
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210 other demo tasks) are able to execute to ensure they either block
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211 (where a block time is specified) or return an error (where no
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212 block time is specified) as the mutex is held by this task. */
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213 vTaskDelay( recmuSHORT_DELAY );
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216 /* For each time we took the mutex, give it back. */
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217 for( ux = 0; ux < recmuMAX_COUNT; ux++ )
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219 /* Ensure the other task attempting to access the mutex (and the
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220 other demo tasks) are able to execute. */
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221 vTaskDelay( recmuSHORT_DELAY );
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223 /* We should now be able to give the mutex as many times as we
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224 took it. When the mutex is available again the Blocking task
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225 should be unblocked but not run because it has a lower priority
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226 than this task. The polling task should also not run at this point
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227 as it too has a lower priority than this task. */
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228 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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230 xErrorOccurred = pdTRUE;
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234 /* Having given it back the same number of times as it was taken, we
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235 should no longer be the mutex owner, so the next give sh ould fail. */
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236 if( xSemaphoreGiveRecursive( xMutex ) == pdPASS )
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238 xErrorOccurred = pdTRUE;
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241 /* Keep count of the number of cycles this task has performed so a
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242 stall can be detected. */
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243 uxControllingCycles++;
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245 /* Suspend ourselves to the blocking task can execute. */
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246 xControllingIsSuspended = pdTRUE;
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247 vTaskSuspend( NULL );
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248 xControllingIsSuspended = pdFALSE;
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251 /*-----------------------------------------------------------*/
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253 static void prvRecursiveMutexBlockingTask( void *pvParameters )
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255 /* Just to remove compiler warning. */
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256 ( void ) pvParameters;
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260 /* This task will run while the controlling task is blocked, and the
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261 controlling task will block only once it has the mutex - therefore
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262 this call should block until the controlling task has given up the
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263 mutex, and not actually execute past this call until the controlling
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264 task is suspended. */
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265 if( xSemaphoreTakeRecursive( xMutex, portMAX_DELAY ) == pdPASS )
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267 if( xControllingIsSuspended != pdTRUE )
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269 /* Did not expect to execute until the controlling task was
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271 xErrorOccurred = pdTRUE;
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275 /* Give the mutex back before suspending ourselves to allow
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276 the polling task to obtain the mutex. */
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277 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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279 xErrorOccurred = pdTRUE;
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282 xBlockingIsSuspended = pdTRUE;
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283 vTaskSuspend( NULL );
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284 xBlockingIsSuspended = pdFALSE;
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289 /* We should not leave the xSemaphoreTakeRecursive() function
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290 until the mutex was obtained. */
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291 xErrorOccurred = pdTRUE;
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294 /* The controlling and blocking tasks should be in lock step. */
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295 if( uxControllingCycles != ( uxBlockingCycles + 1 ) )
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297 xErrorOccurred = pdTRUE;
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300 /* Keep count of the number of cycles this task has performed so a
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301 stall can be detected. */
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302 uxBlockingCycles++;
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305 /*-----------------------------------------------------------*/
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307 static void prvRecursiveMutexPollingTask( void *pvParameters )
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309 /* Just to remove compiler warning. */
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310 ( void ) pvParameters;
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314 /* Keep attempting to obtain the mutex. We should only obtain it when
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315 the blocking task has suspended itself, which in turn should only
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316 happen when the controlling task is also suspended. */
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317 if( xSemaphoreTakeRecursive( xMutex, recmuNO_DELAY ) == pdPASS )
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319 /* Is the blocking task suspended? */
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320 if( ( xBlockingIsSuspended != pdTRUE ) || ( xControllingIsSuspended != pdTRUE ) )
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322 xErrorOccurred = pdTRUE;
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326 /* Keep count of the number of cycles this task has performed
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327 so a stall can be detected. */
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330 /* We can resume the other tasks here even though they have a
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331 higher priority than the polling task. When they execute they
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332 will attempt to obtain the mutex but fail because the polling
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333 task is still the mutex holder. The polling task (this task)
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334 will then inherit the higher priority. The Blocking task will
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335 block indefinitely when it attempts to obtain the mutex, the
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336 Controlling task will only block for a fixed period and an
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337 error will be latched if the polling task has not returned the
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338 mutex by the time this fixed period has expired. */
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339 vTaskResume( xBlockingTaskHandle );
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340 vTaskResume( xControllingTaskHandle );
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342 /* The other two tasks should now have executed and no longer
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344 if( ( xBlockingIsSuspended == pdTRUE ) || ( xControllingIsSuspended == pdTRUE ) )
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346 xErrorOccurred = pdTRUE;
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349 /* Release the mutex, disinheriting the higher priority again. */
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350 if( xSemaphoreGiveRecursive( xMutex ) != pdPASS )
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352 xErrorOccurred = pdTRUE;
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357 #if configUSE_PREEMPTION == 0
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364 /*-----------------------------------------------------------*/
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366 /* This is called to check that all the created tasks are still running. */
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367 portBASE_TYPE xAreRecursiveMutexTasksStillRunning( void )
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369 portBASE_TYPE xReturn;
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370 static unsigned portBASE_TYPE uxLastControllingCycles = 0, uxLastBlockingCycles = 0, uxLastPollingCycles = 0;
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372 /* Is the controlling task still cycling? */
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373 if( uxLastControllingCycles == uxControllingCycles )
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375 xErrorOccurred = pdTRUE;
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379 uxLastControllingCycles = uxControllingCycles;
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382 /* Is the blocking task still cycling? */
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383 if( uxLastBlockingCycles == uxBlockingCycles )
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385 xErrorOccurred = pdTRUE;
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389 uxLastBlockingCycles = uxBlockingCycles;
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392 /* Is the polling task still cycling? */
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393 if( uxLastPollingCycles == uxPollingCycles )
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395 xErrorOccurred = pdTRUE;
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399 uxLastPollingCycles = uxPollingCycles;
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402 if( xErrorOccurred == pdTRUE )
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