2 FreeRTOS V6.1.1 - Copyright (C) 2011 Real Time Engineers Ltd.
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4 ***************************************************************************
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8 * + New to FreeRTOS, *
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9 * + Wanting to learn FreeRTOS or multitasking in general quickly *
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10 * + Looking for basic training, *
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11 * + Wanting to improve your FreeRTOS skills and productivity *
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13 * then take a look at the FreeRTOS books - available as PDF or paperback *
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15 * "Using the FreeRTOS Real Time Kernel - a Practical Guide" *
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16 * http://www.FreeRTOS.org/Documentation *
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18 * A pdf reference manual is also available. Both are usually delivered *
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19 * to your inbox within 20 minutes to two hours when purchased between 8am *
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20 * and 8pm GMT (although please allow up to 24 hours in case of *
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21 * exceptional circumstances). Thank you for your support! *
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23 ***************************************************************************
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25 This file is part of the FreeRTOS distribution.
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27 FreeRTOS is free software; you can redistribute it and/or modify it under
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28 the terms of the GNU General Public License (version 2) as published by the
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29 Free Software Foundation AND MODIFIED BY the FreeRTOS exception.
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30 ***NOTE*** The exception to the GPL is included to allow you to distribute
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31 a combined work that includes FreeRTOS without being obliged to provide the
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32 source code for proprietary components outside of the FreeRTOS kernel.
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33 FreeRTOS is distributed in the hope that it will be useful, but WITHOUT
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34 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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35 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
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36 more details. You should have received a copy of the GNU General Public
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37 License and the FreeRTOS license exception along with FreeRTOS; if not it
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38 can be viewed here: http://www.freertos.org/a00114.html and also obtained
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39 by writing to Richard Barry, contact details for whom are available on the
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44 http://www.FreeRTOS.org - Documentation, latest information, license and
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47 http://www.SafeRTOS.com - A version that is certified for use in safety
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50 http://www.OpenRTOS.com - Commercial support, development, porting,
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51 licensing and training services.
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54 /* Defining MPU_WRAPPERS_INCLUDED_FROM_API_FILE prevents task.h from redefining
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55 all the API functions to use the MPU wrappers. That should only be done when
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56 task.h is included from an application file. */
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57 #define MPU_WRAPPERS_INCLUDED_FROM_API_FILE
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59 #include "FreeRTOS.h"
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64 #undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE
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66 /* Misc definitions. */
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67 #define tmrNO_DELAY ( portTickType ) 0U
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69 /* The definition of the timers themselves. */
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70 typedef struct tmrTimerControl
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72 const signed char *pcTimerName; /*<< Text name. This is not used by the kernel, it is included simply to make debugging easier. */
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73 xListItem xTimerListItem; /*<< Standard linked list item as used by all kernel features for event management. */
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74 portTickType xTimerPeriodInTicks;/*<< How quickly and often the timer expires. */
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75 unsigned portBASE_TYPE uxAutoReload; /*<< Set to pdTRUE if the timer should be automatically restarted once expired. Set to pdFALSE if the timer is, in effect, a one shot timer. */
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76 void *pvTimerID; /*<< An ID to identify the timer. This allows the timer to be identified when the same callback is used for multiple timers. */
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77 tmrTIMER_CALLBACK pxCallbackFunction; /*<< The function that will be called when the timer expires. */
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80 /* The definition of messages that can be sent and received on the timer
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82 typedef struct tmrTimerQueueMessage
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84 portBASE_TYPE xMessageID; /*<< The command being sent to the timer service task. */
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85 portTickType xMessageValue; /*<< An optional value used by a subset of commands, for example, when changing the period of a timer. */
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86 xTIMER * pxTimer; /*<< The timer to which the command will be applied. */
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90 /* The list in which active timers are stored. Timers are referenced in expire
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91 time order, with the nearest expiry time at the front of the list. Only the
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92 timer service task is allowed to access xActiveTimerList. */
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93 PRIVILEGED_DATA static xList xActiveTimerList1;
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94 PRIVILEGED_DATA static xList xActiveTimerList2;
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95 PRIVILEGED_DATA static xList *pxCurrentTimerList;
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96 PRIVILEGED_DATA static xList *pxOverflowTimerList;
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98 /* A queue that is used to send commands to the timer service task. */
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99 PRIVILEGED_DATA static xQueueHandle xTimerQueue = NULL;
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101 /*-----------------------------------------------------------*/
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104 * Initialise the infrastructure used by the timer service task if it has not
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105 * been initialised already.
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107 static void prvCheckForValidListAndQueue( void ) PRIVILEGED_FUNCTION;
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110 * The timer service task (daemon). Timer functionality is controlled by this
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111 * task. Other tasks communicate with the timer service task using the
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112 * xTimerQueue queue.
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114 static void prvTimerTask( void *pvParameters ) PRIVILEGED_FUNCTION;
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117 * Called by the timer service task to interpret and process a command it
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118 * received on the timer queue.
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120 static void prvProcessReceivedCommands( void ) PRIVILEGED_FUNCTION;
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123 * Insert the timer into either xActiveTimerList1, or xActiveTimerList2,
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124 * depending on if the expire time causes a timer counter overflow.
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126 static portBASE_TYPE prvInsertTimerInActiveList( xTIMER *pxTimer, portTickType xNextExpiryTime, portTickType xTimeNow, portTickType xCommandTime ) PRIVILEGED_FUNCTION;
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129 * An active timer has reached its expire time. Reload the timer if it is an
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130 * auto reload timer, then call its callback.
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132 static void prvProcessExpiredTimer( portTickType xNextExpireTime, portTickType xTimeNow ) PRIVILEGED_FUNCTION;
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135 * The tick count has overflowed. Switch the timer lists after ensuring the
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136 * current timer list does not still reference some timers.
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138 static void prvSwitchTimerLists( portTickType xTimeNow, portTickType xLastTime ) PRIVILEGED_FUNCTION;
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141 * Obtain the current tick count, setting *pxTimerListsWereSwitched to pdTRUE
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142 * if a tick count overflow occurred since prvSampleTimeNow() was last called.
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144 static portTickType prvSampleTimeNow( portBASE_TYPE *pxTimerListsWereSwitched ) PRIVILEGED_FUNCTION;
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147 * If the timer list contains any active timers then return the expire time of
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148 * the timer that will expire first and set *pxListWasEmpty to false. If the
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149 * timer list does not contain any timers then return 0 and set *pxListWasEmpty
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152 static portTickType prvLookForExpiredTimer( portBASE_TYPE *pxListWasEmpty ) PRIVILEGED_FUNCTION;
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155 * If a timer has expired, process it. Otherwise, block the timer service task
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156 * until either a timer does expire or a command is received.
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158 static void prvProcessTimerOrBlockTask( portTickType xNextExpireTime, portBASE_TYPE xListWasEmpty ) PRIVILEGED_FUNCTION;
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160 /*-----------------------------------------------------------*/
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162 portBASE_TYPE xTimerCreateTimerTask( void )
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164 portBASE_TYPE xReturn = pdFAIL;
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166 /* This function is called when the scheduler is started if
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167 configUSE_TIMERS is set to 1. Check that the infrastructure used by the
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168 timer service task has been created/initialised. If timers have already
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169 been created then the initialisation will already have been performed. */
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170 prvCheckForValidListAndQueue();
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172 if( xTimerQueue != NULL )
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174 xReturn = xTaskCreate( prvTimerTask, ( const signed char * ) "Tmr Svc", configTIMER_TASK_STACK_DEPTH, NULL, configTIMER_TASK_PRIORITY, NULL);
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179 /*-----------------------------------------------------------*/
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181 xTimerHandle xTimerCreate( const signed char *pcTimerName, portTickType xTimerPeriodInTicks, unsigned portBASE_TYPE uxAutoReload, void *pvTimerID, tmrTIMER_CALLBACK pxCallbackFunction )
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183 xTIMER *pxNewTimer;
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185 /* Allocate the timer structure. */
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186 if( xTimerPeriodInTicks == ( portTickType ) 0U )
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189 configASSERT( ( xTimerPeriodInTicks > 0 ) );
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193 pxNewTimer = ( xTIMER * ) pvPortMalloc( sizeof( xTIMER ) );
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194 if( pxNewTimer != NULL )
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196 /* Ensure the infrastructure used by the timer service task has been
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197 created/initialised. */
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198 prvCheckForValidListAndQueue();
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200 configASSERT( ( xTimerPeriodInTicks > 0 ) );
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202 /* Initialise the timer structure members using the function parameters. */
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203 pxNewTimer->pcTimerName = pcTimerName;
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204 pxNewTimer->xTimerPeriodInTicks = xTimerPeriodInTicks;
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205 pxNewTimer->uxAutoReload = uxAutoReload;
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206 pxNewTimer->pvTimerID = pvTimerID;
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207 pxNewTimer->pxCallbackFunction = pxCallbackFunction;
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208 vListInitialiseItem( &( pxNewTimer->xTimerListItem ) );
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212 return ( xTimerHandle ) pxNewTimer;
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214 /*-----------------------------------------------------------*/
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216 portBASE_TYPE xTimerGenericCommand( xTimerHandle xTimer, portBASE_TYPE xCommandID, portTickType xOptionalValue, portBASE_TYPE *pxHigherPriorityTaskWoken, portTickType xBlockTime )
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218 portBASE_TYPE xReturn = pdFAIL;
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219 xTIMER_MESSAGE xMessage;
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221 /* Send a message to the timer service task to perform a particular action
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222 on a particular timer definition. */
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223 if( xTimerQueue != NULL )
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225 /* Send a command to the timer service task to start the xTimer timer. */
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226 xMessage.xMessageID = xCommandID;
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227 xMessage.xMessageValue = xOptionalValue;
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228 xMessage.pxTimer = ( xTIMER * ) xTimer;
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230 if( pxHigherPriorityTaskWoken == NULL )
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232 if( xTaskGetSchedulerState() == taskSCHEDULER_RUNNING )
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234 xReturn = xQueueSendToBack( xTimerQueue, &xMessage, xBlockTime );
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238 xReturn = xQueueSendToBack( xTimerQueue, &xMessage, tmrNO_DELAY );
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243 xReturn = xQueueSendToBackFromISR( xTimerQueue, &xMessage, pxHigherPriorityTaskWoken );
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249 /*-----------------------------------------------------------*/
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251 static void prvProcessExpiredTimer( portTickType xNextExpireTime, portTickType xTimeNow )
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255 /* Remove the timer from the list of active timers. A check has already
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256 been performed to ensure the list is not empty. */
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257 pxTimer = ( xTIMER * ) listGET_OWNER_OF_HEAD_ENTRY( pxCurrentTimerList );
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258 vListRemove( &( pxTimer->xTimerListItem ) );
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260 /* If the timer is an auto reload timer then calculate the next
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261 expiry time and re-insert the timer in the list of active timers. */
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262 if( pxTimer->uxAutoReload == pdTRUE )
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264 /* This is the only time a timer is inserted into a list using
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265 a time relative to anything other than the current time. It
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266 will therefore be inserted into the correct list relative to
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267 the time this task thinks it is now, even if a command to
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268 switch lists due to a tick count overflow is already waiting in
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269 the timer queue. */
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270 if( prvInsertTimerInActiveList( pxTimer, ( xNextExpireTime + pxTimer->xTimerPeriodInTicks ), xTimeNow, xNextExpireTime ) == pdTRUE )
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272 /* The timer expired before it was added to the active timer
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273 list. Reload it now. The callback will get executed before
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274 this function exits. */
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275 if( pxTimer->uxAutoReload == pdTRUE )
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277 xTimerGenericCommand( pxTimer, tmrCOMMAND_START, xNextExpireTime, NULL, tmrNO_DELAY ); /* Should it be xNextExpireTime or ( xNextExpireTime + pxTimer->xTimerPeriodInTicks )? I think the former. */
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282 /* Call the timer callback. */
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283 pxTimer->pxCallbackFunction( ( xTimerHandle ) pxTimer );
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285 /*-----------------------------------------------------------*/
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287 static void prvTimerTask( void *pvParameters )
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289 portTickType xNextExpireTime;
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290 portBASE_TYPE xListWasEmpty;
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292 /* Just to avoid compiler warnings. */
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293 ( void ) pvParameters;
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297 /* Query the timers list to see if it contains any timers, and if so,
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298 obtain the time at which the next timer will expire. */
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299 xNextExpireTime = prvLookForExpiredTimer( &xListWasEmpty );
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301 /* If a timer has expired, process it. Otherwise, block this task
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302 until either a timer does expire, or a command is received. */
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303 prvProcessTimerOrBlockTask( xNextExpireTime, xListWasEmpty );
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305 /* Empty the command queue. */
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306 prvProcessReceivedCommands();
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309 /*-----------------------------------------------------------*/
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311 static void prvProcessTimerOrBlockTask( portTickType xNextExpireTime, portBASE_TYPE xListWasEmpty )
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313 portTickType xTimeNow;
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314 portBASE_TYPE xTimerListsWereSwitched;
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318 /* Obtain the time now to make an assessment as to whether the timer
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319 has expired or not. If obtaining the time causes the lists to switch
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320 then don't process this timer as any timers that remained in the list
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321 when the lists were switched will have been processed within the
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322 prvSampelTimeNow() function. */
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323 xTimeNow = prvSampleTimeNow( &xTimerListsWereSwitched );
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324 if( xTimerListsWereSwitched == pdFALSE )
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326 /* The tick count has not overflowed, has the timer expired? */
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327 if( ( xListWasEmpty == pdFALSE ) && ( xNextExpireTime <= xTimeNow ) )
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329 prvProcessExpiredTimer( xNextExpireTime, xTimeNow );
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333 /* The tick count has not overflowed, and the next expire
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334 time has not been reached yet. This task should therefore
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335 block to wait for the next expire time or a command to be
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336 received - whichever comes first. The following line cannot
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337 be reached unless xNextExpireTime > xTimeNow, except in the
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338 case when the current timer list is empty. */
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339 vQueueWaitForMessageRestricted( xTimerQueue, ( xNextExpireTime - xTimeNow ) );
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343 if( xTaskResumeAll() == pdFALSE )
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345 /* Yield to wait for either a command to arrive, or the block time
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346 to expire. If a command arrived between the critical section being
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347 exited and this yield then the yield will not cause the task
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349 portYIELD_WITHIN_API();
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352 /*-----------------------------------------------------------*/
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354 static portTickType prvLookForExpiredTimer( portBASE_TYPE *pxListWasEmpty )
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356 portTickType xNextExpireTime;
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358 /* Timers are listed in expiry time order, with the head of the list
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359 referencing the task that will expire first. Obtain the time at which
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360 the timer with the nearest expiry time will expire. If there are no
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361 active timers then just set the next expire time to 0. That will cause
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362 this task to unblock when the tick count overflows, at which point the
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363 timer lists will be switched and the next expiry time can be
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365 *pxListWasEmpty = listLIST_IS_EMPTY( pxCurrentTimerList );
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366 if( *pxListWasEmpty == pdFALSE )
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368 xNextExpireTime = listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxCurrentTimerList );
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372 /* Ensure the task unblocks when the tick count rolls over. */
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373 xNextExpireTime = ( portTickType ) 0U;
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376 return xNextExpireTime;
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378 /*-----------------------------------------------------------*/
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380 static portTickType prvSampleTimeNow( portBASE_TYPE *pxTimerListsWereSwitched )
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382 portTickType xTimeNow;
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383 static portTickType xLastTime = ( portTickType ) 0U;
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385 xTimeNow = xTaskGetTickCount();
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387 if( xTimeNow < xLastTime )
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389 prvSwitchTimerLists( xTimeNow, xLastTime );
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390 *pxTimerListsWereSwitched = pdTRUE;
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394 *pxTimerListsWereSwitched = pdFALSE;
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397 xLastTime = xTimeNow;
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401 /*-----------------------------------------------------------*/
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403 static portBASE_TYPE prvInsertTimerInActiveList( xTIMER *pxTimer, portTickType xNextExpiryTime, portTickType xTimeNow, portTickType xCommandTime )
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405 portBASE_TYPE xProcessTimerNow = pdFALSE;
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407 listSET_LIST_ITEM_VALUE( &( pxTimer->xTimerListItem ), xNextExpiryTime );
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408 listSET_LIST_ITEM_OWNER( &( pxTimer->xTimerListItem ), pxTimer );
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410 if( xNextExpiryTime <= xTimeNow )
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412 /* Has the expiry time elapsed between the command to start/reset a
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413 timer was issued, and the time the command was processed? */
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414 if( ( ( portTickType ) ( xTimeNow - xCommandTime ) ) >= pxTimer->xTimerPeriodInTicks )
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416 /* The time between a command being issued and the command being
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417 processed actually exceeds the timers period. */
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418 xProcessTimerNow = pdTRUE;
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422 vListInsert( pxOverflowTimerList, &( pxTimer->xTimerListItem ) );
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427 if( ( xTimeNow < xCommandTime ) && ( xNextExpiryTime >= xCommandTime ) )
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429 /* If, since the command was issued, the tick count has overflowed
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430 but the expiry time has not, then the timer must have already passed
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431 its expiry time and should be processed immediately. */
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432 xProcessTimerNow = pdTRUE;
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436 vListInsert( pxCurrentTimerList, &( pxTimer->xTimerListItem ) );
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440 return xProcessTimerNow;
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442 /*-----------------------------------------------------------*/
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444 static void prvProcessReceivedCommands( void )
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446 xTIMER_MESSAGE xMessage;
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448 portBASE_TYPE xTimerListsWereSwitched;
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449 portTickType xTimeNow;
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451 /* In this case the xTimerListsWereSwitched parameter is not used, but it
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452 must be present in the function call. */
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453 xTimeNow = prvSampleTimeNow( &xTimerListsWereSwitched );
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455 while( xQueueReceive( xTimerQueue, &xMessage, tmrNO_DELAY ) != pdFAIL )
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457 pxTimer = xMessage.pxTimer;
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459 /* Is the timer already in a list of active timers? When the command
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460 is trmCOMMAND_PROCESS_TIMER_OVERFLOW, the timer will be NULL as the
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461 command is to the task rather than to an individual timer. */
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462 if( pxTimer != NULL )
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464 if( listIS_CONTAINED_WITHIN( NULL, &( pxTimer->xTimerListItem ) ) == pdFALSE )
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466 /* The timer is in a list, remove it. */
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467 vListRemove( &( pxTimer->xTimerListItem ) );
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471 switch( xMessage.xMessageID )
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473 case tmrCOMMAND_START :
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474 /* Start or restart a timer. */
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475 if( prvInsertTimerInActiveList( pxTimer, xMessage.xMessageValue + pxTimer->xTimerPeriodInTicks, xTimeNow, xMessage.xMessageValue ) == pdTRUE )
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477 /* The timer expired before it was added to the active timer
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478 list. Process it now. */
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479 pxTimer->pxCallbackFunction( ( xTimerHandle ) pxTimer );
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481 if( pxTimer->uxAutoReload == pdTRUE )
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483 xTimerGenericCommand( pxTimer, tmrCOMMAND_START, xMessage.xMessageValue + pxTimer->xTimerPeriodInTicks, NULL, tmrNO_DELAY );
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488 case tmrCOMMAND_STOP :
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489 /* The timer has already been removed from the active list.
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490 There is nothing to do here. */
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493 case tmrCOMMAND_CHANGE_PERIOD :
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494 pxTimer->xTimerPeriodInTicks = xMessage.xMessageValue;
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495 configASSERT( ( pxTimer->xTimerPeriodInTicks > 0 ) );
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496 prvInsertTimerInActiveList( pxTimer, ( xTimeNow + pxTimer->xTimerPeriodInTicks ), xTimeNow, xTimeNow );
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499 case tmrCOMMAND_DELETE :
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500 /* The timer has already been removed from the active list,
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501 just free up the memory. */
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502 vPortFree( pxTimer );
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506 /* Don't expect to get here. */
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511 /*-----------------------------------------------------------*/
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513 static void prvSwitchTimerLists( portTickType xTimeNow, portTickType xLastTime )
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515 portTickType xNextExpireTime;
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518 /* Remove compiler warnings if configASSERT() is not defined. */
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519 ( void ) xLastTime;
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521 /* The tick count has overflowed. The timer lists must be switched.
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522 If there are any timers still referenced from the current timer list
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523 then they must have expired and should be processed before the lists
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525 while( listLIST_IS_EMPTY( pxCurrentTimerList ) == pdFALSE )
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527 xNextExpireTime = listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxCurrentTimerList );
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528 configASSERT( ( xNextExpireTime >= xLastTime ) );
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529 prvProcessExpiredTimer( xNextExpireTime, xTimeNow );
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532 pxTemp = pxCurrentTimerList;
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533 pxCurrentTimerList = pxOverflowTimerList;
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534 pxOverflowTimerList = pxTemp;
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536 /*-----------------------------------------------------------*/
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538 static void prvCheckForValidListAndQueue( void )
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540 /* Check that the list from which active timers are referenced, and the
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541 queue used to communicate with the timer service, have been
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543 taskENTER_CRITICAL();
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545 if( xTimerQueue == NULL )
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547 vListInitialise( &xActiveTimerList1 );
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548 vListInitialise( &xActiveTimerList2 );
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549 pxCurrentTimerList = &xActiveTimerList1;
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550 pxOverflowTimerList = &xActiveTimerList2;
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551 xTimerQueue = xQueueCreate( configTIMER_QUEUE_LENGTH, sizeof( xTIMER_MESSAGE ) );
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554 taskEXIT_CRITICAL();
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556 /*-----------------------------------------------------------*/
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558 portBASE_TYPE xTimerIsTimerActive( xTimerHandle xTimer )
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560 portBASE_TYPE xTimerIsInActiveList;
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561 xTIMER *pxTimer = ( xTIMER * ) xTimer;
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563 /* Is the timer in the list of active timers? */
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564 taskENTER_CRITICAL();
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566 /* Checking to see if it is in the NULL list in effect checks to see if
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567 it is referenced from either the current or the overflow timer lists in
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568 one go, but the logic has to be reversed, hence the '!'. */
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569 xTimerIsInActiveList = !( listIS_CONTAINED_WITHIN( NULL, &( pxTimer->xTimerListItem ) ) );
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571 taskEXIT_CRITICAL();
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573 return xTimerIsInActiveList;
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575 /*-----------------------------------------------------------*/
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577 void *pvTimerGetTimerID( xTimerHandle xTimer )
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579 xTIMER *pxTimer = ( xTIMER * ) xTimer;
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581 return pxTimer->pvTimerID;
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583 /*-----------------------------------------------------------*/
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