2 FreeRTOS V7.1.1 - Copyright (C) 2012 Real Time Engineers Ltd.
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5 ***************************************************************************
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7 * FreeRTOS tutorial books are available in pdf and paperback. *
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8 * Complete, revised, and edited pdf reference manuals are also *
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11 * Purchasing FreeRTOS documentation will not only help you, by *
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12 * ensuring you get running as quickly as possible and with an *
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13 * in-depth knowledge of how to use FreeRTOS, it will also help *
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14 * the FreeRTOS project to continue with its mission of providing *
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15 * professional grade, cross platform, de facto standard solutions *
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16 * for microcontrollers - completely free of charge! *
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18 * >>> See http://www.FreeRTOS.org/Documentation for details. <<< *
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20 * Thank you for using FreeRTOS, and thank you for your support! *
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22 ***************************************************************************
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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 modification to the GPL is included to allow you to
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31 distribute a combined work that includes FreeRTOS without being obliged to
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32 provide the source code for proprietary components outside of the FreeRTOS
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33 kernel. FreeRTOS is distributed in the hope that it will be useful, but
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34 WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
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35 or 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 ***************************************************************************
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46 * Having a problem? Start by reading the FAQ "My application does *
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47 * not run, what could be wrong? *
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49 * http://www.FreeRTOS.org/FAQHelp.html *
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51 ***************************************************************************
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54 http://www.FreeRTOS.org - Documentation, training, latest information,
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55 license and contact details.
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57 http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
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58 including FreeRTOS+Trace - an indispensable productivity tool.
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60 Real Time Engineers ltd license FreeRTOS to High Integrity Systems, who sell
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61 the code with commercial support, indemnification, and middleware, under
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62 the OpenRTOS brand: http://www.OpenRTOS.com. High Integrity Systems also
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63 provide a safety engineered and independently SIL3 certified version under
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64 the SafeRTOS brand: http://www.SafeRTOS.com.
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68 * Creates two sets of two tasks. The tasks within a set share a variable, access
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69 * to which is guarded by a semaphore.
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71 * Each task starts by attempting to obtain the semaphore. On obtaining a
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72 * semaphore a task checks to ensure that the guarded variable has an expected
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73 * value. It then clears the variable to zero before counting it back up to the
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74 * expected value in increments of 1. After each increment the variable is checked
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75 * to ensure it contains the value to which it was just set. When the starting
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76 * value is again reached the task releases the semaphore giving the other task in
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77 * the set a chance to do exactly the same thing. The starting value is high
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78 * enough to ensure that a tick is likely to occur during the incrementing loop.
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80 * An error is flagged if at any time during the process a shared variable is
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81 * found to have a value other than that expected. Such an occurrence would
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82 * suggest an error in the mutual exclusion mechanism by which access to the
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83 * variable is restricted.
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85 * The first set of two tasks poll their semaphore. The second set use blocking
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88 * \page SemTestC semtest.c
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89 * \ingroup DemoFiles
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94 Changes from V1.2.0:
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96 + The tasks that operate at the idle priority now use a lower expected
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97 count than those running at a higher priority. This prevents the low
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98 priority tasks from signaling an error because they have not been
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99 scheduled enough time for each of them to count the shared variable to
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102 Changes from V2.0.0
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104 + Delay periods are now specified using variables and constants of
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105 portTickType rather than unsigned long.
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107 Changes from V2.1.1
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109 + The stack size now uses configMINIMAL_STACK_SIZE.
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110 + String constants made file scope to decrease stack depth on 8051 port.
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113 #include <stdlib.h>
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115 /* Scheduler include files. */
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116 #include "FreeRTOS.h"
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118 #include "semphr.h"
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120 /* Demo app include files. */
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121 #include "semtest.h"
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124 /* The value to which the shared variables are counted. */
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125 #define semtstBLOCKING_EXPECTED_VALUE ( ( unsigned long ) 0xfff )
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126 #define semtstNON_BLOCKING_EXPECTED_VALUE ( ( unsigned long ) 0xff )
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128 #define semtstSTACK_SIZE configMINIMAL_STACK_SIZE
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130 #define semtstNUM_TASKS ( 4 )
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132 #define semtstDELAY_FACTOR ( ( portTickType ) 10 )
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134 /* The task function as described at the top of the file. */
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135 static void prvSemaphoreTest( void *pvParameters );
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137 /* Structure used to pass parameters to each task. */
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138 typedef struct SEMAPHORE_PARAMETERS
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140 xSemaphoreHandle xSemaphore;
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141 volatile unsigned long *pulSharedVariable;
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142 portTickType xBlockTime;
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143 } xSemaphoreParameters;
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145 /* Variables used to check that all the tasks are still running without errors. */
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146 static volatile short sCheckVariables[ semtstNUM_TASKS ] = { 0 };
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147 static volatile short sNextCheckVariable = 0;
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149 /* Strings to print if USE_STDIO is defined. */
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150 const char * const pcPollingSemaphoreTaskError = "Guarded shared variable in unexpected state.\r\n";
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151 const char * const pcSemaphoreTaskStart = "Guarded shared variable task started.\r\n";
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153 /*-----------------------------------------------------------*/
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155 void vStartSemaphoreTasks( unsigned portBASE_TYPE uxPriority )
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157 xSemaphoreParameters *pxFirstSemaphoreParameters, *pxSecondSemaphoreParameters;
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158 const portTickType xBlockTime = ( portTickType ) 100;
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160 /* Create the structure used to pass parameters to the first two tasks. */
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161 pxFirstSemaphoreParameters = ( xSemaphoreParameters * ) pvPortMalloc( sizeof( xSemaphoreParameters ) );
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163 if( pxFirstSemaphoreParameters != NULL )
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165 /* Create the semaphore used by the first two tasks. */
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166 vSemaphoreCreateBinary( pxFirstSemaphoreParameters->xSemaphore );
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168 if( pxFirstSemaphoreParameters->xSemaphore != NULL )
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170 /* Create the variable which is to be shared by the first two tasks. */
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171 pxFirstSemaphoreParameters->pulSharedVariable = ( unsigned long * ) pvPortMalloc( sizeof( unsigned long ) );
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173 /* Initialise the share variable to the value the tasks expect. */
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174 *( pxFirstSemaphoreParameters->pulSharedVariable ) = semtstNON_BLOCKING_EXPECTED_VALUE;
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176 /* The first two tasks do not block on semaphore calls. */
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177 pxFirstSemaphoreParameters->xBlockTime = ( portTickType ) 0;
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179 /* Spawn the first two tasks. As they poll they operate at the idle priority. */
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180 xTaskCreate( prvSemaphoreTest, "PolSEM1", semtstSTACK_SIZE, ( void * ) pxFirstSemaphoreParameters, tskIDLE_PRIORITY, ( xTaskHandle * ) NULL );
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181 xTaskCreate( prvSemaphoreTest, "PolSEM2", semtstSTACK_SIZE, ( void * ) pxFirstSemaphoreParameters, tskIDLE_PRIORITY, ( xTaskHandle * ) NULL );
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185 /* Do exactly the same to create the second set of tasks, only this time
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186 provide a block time for the semaphore calls. */
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187 pxSecondSemaphoreParameters = ( xSemaphoreParameters * ) pvPortMalloc( sizeof( xSemaphoreParameters ) );
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188 if( pxSecondSemaphoreParameters != NULL )
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190 vSemaphoreCreateBinary( pxSecondSemaphoreParameters->xSemaphore );
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192 if( pxSecondSemaphoreParameters->xSemaphore != NULL )
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194 pxSecondSemaphoreParameters->pulSharedVariable = ( unsigned long * ) pvPortMalloc( sizeof( unsigned long ) );
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195 *( pxSecondSemaphoreParameters->pulSharedVariable ) = semtstBLOCKING_EXPECTED_VALUE;
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196 pxSecondSemaphoreParameters->xBlockTime = xBlockTime / portTICK_RATE_MS;
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198 xTaskCreate( prvSemaphoreTest, "BlkSEM1", semtstSTACK_SIZE, ( void * ) pxSecondSemaphoreParameters, uxPriority, ( xTaskHandle * ) NULL );
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199 xTaskCreate( prvSemaphoreTest, "BlkSEM2", semtstSTACK_SIZE, ( void * ) pxSecondSemaphoreParameters, uxPriority, ( xTaskHandle * ) NULL );
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203 /*-----------------------------------------------------------*/
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205 static void prvSemaphoreTest( void *pvParameters )
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207 xSemaphoreParameters *pxParameters;
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208 volatile unsigned long *pulSharedVariable, ulExpectedValue;
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209 unsigned long ulCounter;
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210 short sError = pdFALSE, sCheckVariableToUse;
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212 /* See which check variable to use. sNextCheckVariable is not semaphore
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214 portENTER_CRITICAL();
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215 sCheckVariableToUse = sNextCheckVariable;
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216 sNextCheckVariable++;
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217 portEXIT_CRITICAL();
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219 /* Queue a message for printing to say the task has started. */
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220 vPrintDisplayMessage( &pcSemaphoreTaskStart );
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222 /* A structure is passed in as the parameter. This contains the shared
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223 variable being guarded. */
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224 pxParameters = ( xSemaphoreParameters * ) pvParameters;
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225 pulSharedVariable = pxParameters->pulSharedVariable;
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227 /* If we are blocking we use a much higher count to ensure loads of context
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228 switches occur during the count. */
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229 if( pxParameters->xBlockTime > ( portTickType ) 0 )
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231 ulExpectedValue = semtstBLOCKING_EXPECTED_VALUE;
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235 ulExpectedValue = semtstNON_BLOCKING_EXPECTED_VALUE;
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240 /* Try to obtain the semaphore. */
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241 if( xSemaphoreTake( pxParameters->xSemaphore, pxParameters->xBlockTime ) == pdPASS )
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243 /* We have the semaphore and so expect any other tasks using the
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244 shared variable to have left it in the state we expect to find
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246 if( *pulSharedVariable != ulExpectedValue )
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248 vPrintDisplayMessage( &pcPollingSemaphoreTaskError );
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252 /* Clear the variable, then count it back up to the expected value
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253 before releasing the semaphore. Would expect a context switch or
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254 two during this time. */
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255 for( ulCounter = ( unsigned long ) 0; ulCounter <= ulExpectedValue; ulCounter++ )
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257 *pulSharedVariable = ulCounter;
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258 if( *pulSharedVariable != ulCounter )
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260 if( sError == pdFALSE )
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262 vPrintDisplayMessage( &pcPollingSemaphoreTaskError );
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268 /* Release the semaphore, and if no errors have occurred increment the check
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270 if( xSemaphoreGive( pxParameters->xSemaphore ) == pdFALSE )
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272 vPrintDisplayMessage( &pcPollingSemaphoreTaskError );
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276 if( sError == pdFALSE )
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278 if( sCheckVariableToUse < semtstNUM_TASKS )
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280 ( sCheckVariables[ sCheckVariableToUse ] )++;
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284 /* If we have a block time then we are running at a priority higher
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285 than the idle priority. This task takes a long time to complete
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286 a cycle (deliberately so to test the guarding) so will be starving
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287 out lower priority tasks. Block for some time to allow give lower
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288 priority tasks some processor time. */
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289 vTaskDelay( pxParameters->xBlockTime * semtstDELAY_FACTOR );
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293 if( pxParameters->xBlockTime == ( portTickType ) 0 )
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295 /* We have not got the semaphore yet, so no point using the
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296 processor. We are not blocking when attempting to obtain the
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303 /*-----------------------------------------------------------*/
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305 /* This is called to check that all the created tasks are still running. */
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306 portBASE_TYPE xAreSemaphoreTasksStillRunning( void )
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308 static short sLastCheckVariables[ semtstNUM_TASKS ] = { 0 };
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309 portBASE_TYPE xTask, xReturn = pdTRUE;
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311 for( xTask = 0; xTask < semtstNUM_TASKS; xTask++ )
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313 if( sLastCheckVariables[ xTask ] == sCheckVariables[ xTask ] )
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318 sLastCheckVariables[ xTask ] = sCheckVariables[ xTask ];
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