2 FreeRTOS.org V4.6.1 - Copyright (C) 2003-2007 Richard Barry.
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6 FreeRTOS.org is free software; you can redistribute it and/or modify
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7 it under the terms of the GNU General Public License as published by
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8 the Free Software Foundation; either version 2 of the License, or
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11 FreeRTOS.org is distributed in the hope that it will be useful,
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13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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14 GNU General Public License for more details.
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18 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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26 ***************************************************************************
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27 See http://www.FreeRTOS.org for documentation, latest information, license
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28 and contact details. Please ensure to read the configuration and relevant
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29 port sections of the online documentation.
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31 Also see http://www.SafeRTOS.com a version that has been certified for use
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32 in safety critical systems, plus commercial licensing, development and
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34 ***************************************************************************
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38 * Creates two sets of two tasks. The tasks within a set share a variable, access
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39 * to which is guarded by a semaphore.
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41 * Each task starts by attempting to obtain the semaphore. On obtaining a
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42 * semaphore a task checks to ensure that the guarded variable has an expected
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43 * value. It then clears the variable to zero before counting it back up to the
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44 * expected value in increments of 1. After each increment the variable is checked
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45 * to ensure it contains the value to which it was just set. When the starting
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46 * value is again reached the task releases the semaphore giving the other task in
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47 * the set a chance to do exactly the same thing. The starting value is high
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48 * enough to ensure that a tick is likely to occur during the incrementing loop.
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50 * An error is flagged if at any time during the process a shared variable is
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51 * found to have a value other than that expected. Such an occurrence would
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52 * suggest an error in the mutual exclusion mechanism by which access to the
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53 * variable is restricted.
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55 * The first set of two tasks poll their semaphore. The second set use blocking
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58 * \page SemTestC semtest.c
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59 * \ingroup DemoFiles
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64 Changes from V1.2.0:
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66 + The tasks that operate at the idle priority now use a lower expected
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67 count than those running at a higher priority. This prevents the low
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68 priority tasks from signaling an error because they have not been
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69 scheduled enough time for each of them to count the shared variable to
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74 + Delay periods are now specified using variables and constants of
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75 portTickType rather than unsigned portLONG.
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79 + The stack size now uses configMINIMAL_STACK_SIZE.
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80 + String constants made file scope to decrease stack depth on 8051 port.
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85 /* Scheduler include files. */
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86 #include "FreeRTOS.h"
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90 /* Demo app include files. */
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91 #include "semtest.h"
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94 /* The value to which the shared variables are counted. */
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95 #define semtstBLOCKING_EXPECTED_VALUE ( ( unsigned portLONG ) 0xfff )
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96 #define semtstNON_BLOCKING_EXPECTED_VALUE ( ( unsigned portLONG ) 0xff )
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98 #define semtstSTACK_SIZE configMINIMAL_STACK_SIZE
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100 #define semtstNUM_TASKS ( 4 )
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102 #define semtstDELAY_FACTOR ( ( portTickType ) 10 )
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104 /* The task function as described at the top of the file. */
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105 static void prvSemaphoreTest( void *pvParameters );
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107 /* Structure used to pass parameters to each task. */
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108 typedef struct SEMAPHORE_PARAMETERS
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110 xSemaphoreHandle xSemaphore;
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111 volatile unsigned portLONG *pulSharedVariable;
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112 portTickType xBlockTime;
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113 } xSemaphoreParameters;
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115 /* Variables used to check that all the tasks are still running without errors. */
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116 static volatile portSHORT sCheckVariables[ semtstNUM_TASKS ] = { 0 };
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117 static volatile portSHORT sNextCheckVariable = 0;
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119 /* Strings to print if USE_STDIO is defined. */
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120 const portCHAR * const pcPollingSemaphoreTaskError = "Guarded shared variable in unexpected state.\r\n";
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121 const portCHAR * const pcSemaphoreTaskStart = "Guarded shared variable task started.\r\n";
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123 /*-----------------------------------------------------------*/
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125 void vStartSemaphoreTasks( unsigned portBASE_TYPE uxPriority )
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127 xSemaphoreParameters *pxFirstSemaphoreParameters, *pxSecondSemaphoreParameters;
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128 const portTickType xBlockTime = ( portTickType ) 100;
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130 /* Create the structure used to pass parameters to the first two tasks. */
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131 pxFirstSemaphoreParameters = ( xSemaphoreParameters * ) pvPortMalloc( sizeof( xSemaphoreParameters ) );
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133 if( pxFirstSemaphoreParameters != NULL )
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135 /* Create the semaphore used by the first two tasks. */
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136 vSemaphoreCreateBinary( pxFirstSemaphoreParameters->xSemaphore );
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138 if( pxFirstSemaphoreParameters->xSemaphore != NULL )
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140 /* Create the variable which is to be shared by the first two tasks. */
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141 pxFirstSemaphoreParameters->pulSharedVariable = ( unsigned portLONG * ) pvPortMalloc( sizeof( unsigned portLONG ) );
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143 /* Initialise the share variable to the value the tasks expect. */
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144 *( pxFirstSemaphoreParameters->pulSharedVariable ) = semtstNON_BLOCKING_EXPECTED_VALUE;
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146 /* The first two tasks do not block on semaphore calls. */
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147 pxFirstSemaphoreParameters->xBlockTime = ( portTickType ) 0;
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149 /* Spawn the first two tasks. As they poll they operate at the idle priority. */
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150 xTaskCreate( prvSemaphoreTest, "PolSEM1", semtstSTACK_SIZE, ( void * ) pxFirstSemaphoreParameters, tskIDLE_PRIORITY, ( xTaskHandle * ) NULL );
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151 xTaskCreate( prvSemaphoreTest, "PolSEM2", semtstSTACK_SIZE, ( void * ) pxFirstSemaphoreParameters, tskIDLE_PRIORITY, ( xTaskHandle * ) NULL );
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155 /* Do exactly the same to create the second set of tasks, only this time
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156 provide a block time for the semaphore calls. */
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157 pxSecondSemaphoreParameters = ( xSemaphoreParameters * ) pvPortMalloc( sizeof( xSemaphoreParameters ) );
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158 if( pxSecondSemaphoreParameters != NULL )
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160 vSemaphoreCreateBinary( pxSecondSemaphoreParameters->xSemaphore );
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162 if( pxSecondSemaphoreParameters->xSemaphore != NULL )
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164 pxSecondSemaphoreParameters->pulSharedVariable = ( unsigned portLONG * ) pvPortMalloc( sizeof( unsigned portLONG ) );
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165 *( pxSecondSemaphoreParameters->pulSharedVariable ) = semtstBLOCKING_EXPECTED_VALUE;
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166 pxSecondSemaphoreParameters->xBlockTime = xBlockTime / portTICK_RATE_MS;
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168 xTaskCreate( prvSemaphoreTest, "BlkSEM1", semtstSTACK_SIZE, ( void * ) pxSecondSemaphoreParameters, uxPriority, ( xTaskHandle * ) NULL );
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169 xTaskCreate( prvSemaphoreTest, "BlkSEM2", semtstSTACK_SIZE, ( void * ) pxSecondSemaphoreParameters, uxPriority, ( xTaskHandle * ) NULL );
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173 /*-----------------------------------------------------------*/
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175 static void prvSemaphoreTest( void *pvParameters )
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177 xSemaphoreParameters *pxParameters;
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178 volatile unsigned portLONG *pulSharedVariable, ulExpectedValue;
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179 unsigned portLONG ulCounter;
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180 portSHORT sError = pdFALSE, sCheckVariableToUse;
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182 /* See which check variable to use. sNextCheckVariable is not semaphore
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184 portENTER_CRITICAL();
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185 sCheckVariableToUse = sNextCheckVariable;
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186 sNextCheckVariable++;
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187 portEXIT_CRITICAL();
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189 /* Queue a message for printing to say the task has started. */
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190 vPrintDisplayMessage( &pcSemaphoreTaskStart );
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192 /* A structure is passed in as the parameter. This contains the shared
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193 variable being guarded. */
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194 pxParameters = ( xSemaphoreParameters * ) pvParameters;
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195 pulSharedVariable = pxParameters->pulSharedVariable;
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197 /* If we are blocking we use a much higher count to ensure loads of context
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198 switches occur during the count. */
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199 if( pxParameters->xBlockTime > ( portTickType ) 0 )
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201 ulExpectedValue = semtstBLOCKING_EXPECTED_VALUE;
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205 ulExpectedValue = semtstNON_BLOCKING_EXPECTED_VALUE;
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210 /* Try to obtain the semaphore. */
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211 if( xSemaphoreTake( pxParameters->xSemaphore, pxParameters->xBlockTime ) == pdPASS )
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213 /* We have the semaphore and so expect any other tasks using the
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214 shared variable to have left it in the state we expect to find
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216 if( *pulSharedVariable != ulExpectedValue )
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218 vPrintDisplayMessage( &pcPollingSemaphoreTaskError );
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222 /* Clear the variable, then count it back up to the expected value
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223 before releasing the semaphore. Would expect a context switch or
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224 two during this time. */
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225 for( ulCounter = ( unsigned portLONG ) 0; ulCounter <= ulExpectedValue; ulCounter++ )
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227 *pulSharedVariable = ulCounter;
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228 if( *pulSharedVariable != ulCounter )
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230 if( sError == pdFALSE )
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232 vPrintDisplayMessage( &pcPollingSemaphoreTaskError );
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238 /* Release the semaphore, and if no errors have occurred increment the check
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240 if( xSemaphoreGive( pxParameters->xSemaphore ) == pdFALSE )
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242 vPrintDisplayMessage( &pcPollingSemaphoreTaskError );
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246 if( sError == pdFALSE )
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248 if( sCheckVariableToUse < semtstNUM_TASKS )
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250 ( sCheckVariables[ sCheckVariableToUse ] )++;
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254 /* If we have a block time then we are running at a priority higher
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255 than the idle priority. This task takes a long time to complete
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256 a cycle (deliberately so to test the guarding) so will be starving
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257 out lower priority tasks. Block for some time to allow give lower
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258 priority tasks some processor time. */
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259 vTaskDelay( pxParameters->xBlockTime * semtstDELAY_FACTOR );
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263 if( pxParameters->xBlockTime == ( portTickType ) 0 )
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265 /* We have not got the semaphore yet, so no point using the
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266 processor. We are not blocking when attempting to obtain the
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273 /*-----------------------------------------------------------*/
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275 /* This is called to check that all the created tasks are still running. */
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276 portBASE_TYPE xAreSemaphoreTasksStillRunning( void )
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278 static portSHORT sLastCheckVariables[ semtstNUM_TASKS ] = { 0 };
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279 portBASE_TYPE xTask, xReturn = pdTRUE;
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281 for( xTask = 0; xTask < semtstNUM_TASKS; xTask++ )
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283 if( sLastCheckVariables[ xTask ] == sCheckVariables[ xTask ] )
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288 sLastCheckVariables[ xTask ] = sCheckVariables[ xTask ];
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