Diff: Source/timers.c

Revision:

0:8e57f3e9cc89

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Source/timers.c	Fri Jan 24 14:56:04 2014 +0000
@@ -0,0 +1,707 @@
+/*
+    FreeRTOS V7.6.0 - Copyright (C) 2013 Real Time Engineers Ltd. 
+    All rights reserved
+
+    VISIT http://www.FreeRTOS.org TO ENSURE YOU ARE USING THE LATEST VERSION.
+
+    ***************************************************************************
+     *                                                                       *
+     *    FreeRTOS provides completely free yet professionally developed,    *
+     *    robust, strictly quality controlled, supported, and cross          *
+     *    platform software that has become a de facto standard.             *
+     *                                                                       *
+     *    Help yourself get started quickly and support the FreeRTOS         *
+     *    project by purchasing a FreeRTOS tutorial book, reference          *
+     *    manual, or both from: http://www.FreeRTOS.org/Documentation        *
+     *                                                                       *
+     *    Thank you!                                                         *
+     *                                                                       *
+    ***************************************************************************
+
+    This file is part of the FreeRTOS distribution.
+
+    FreeRTOS is free software; you can redistribute it and/or modify it under
+    the terms of the GNU General Public License (version 2) as published by the
+    Free Software Foundation >>!AND MODIFIED BY!<< the FreeRTOS exception.
+
+    >>! NOTE: The modification to the GPL is included to allow you to distribute
+    >>! a combined work that includes FreeRTOS without being obliged to provide
+    >>! the source code for proprietary components outside of the FreeRTOS
+    >>! kernel.
+
+    FreeRTOS is distributed in the hope that it will be useful, but WITHOUT ANY
+    WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+    FOR A PARTICULAR PURPOSE.  Full license text is available from the following
+    link: http://www.freertos.org/a00114.html
+
+    1 tab == 4 spaces!
+
+    ***************************************************************************
+     *                                                                       *
+     *    Having a problem?  Start by reading the FAQ "My application does   *
+     *    not run, what could be wrong?"                                     *
+     *                                                                       *
+     *    http://www.FreeRTOS.org/FAQHelp.html                               *
+     *                                                                       *
+    ***************************************************************************
+
+    http://www.FreeRTOS.org - Documentation, books, training, latest versions,
+    license and Real Time Engineers Ltd. contact details.
+
+    http://www.FreeRTOS.org/plus - A selection of FreeRTOS ecosystem products,
+    including FreeRTOS+Trace - an indispensable productivity tool, a DOS
+    compatible FAT file system, and our tiny thread aware UDP/IP stack.
+
+    http://www.OpenRTOS.com - Real Time Engineers ltd license FreeRTOS to High
+    Integrity Systems to sell under the OpenRTOS brand.  Low cost OpenRTOS
+    licenses offer ticketed support, indemnification and middleware.
+
+    http://www.SafeRTOS.com - High Integrity Systems also provide a safety
+    engineered and independently SIL3 certified version for use in safety and
+    mission critical applications that require provable dependability.
+
+    1 tab == 4 spaces!
+*/
+
+/* Standard includes. */
+#include <stdlib.h>
+
+/* Defining MPU_WRAPPERS_INCLUDED_FROM_API_FILE prevents task.h from redefining
+all the API functions to use the MPU wrappers.  That should only be done when
+task.h is included from an application file. */
+#define MPU_WRAPPERS_INCLUDED_FROM_API_FILE
+
+#include "FreeRTOS.h"
+#include "task.h"
+#include "queue.h"
+#include "timers.h"
+
+/* Lint e961 and e750 are suppressed as a MISRA exception justified because the
+MPU ports require MPU_WRAPPERS_INCLUDED_FROM_API_FILE to be defined for the
+header files above, but not in this file, in order to generate the correct
+privileged Vs unprivileged linkage and placement. */
+#undef MPU_WRAPPERS_INCLUDED_FROM_API_FILE /*lint !e961 !e750. */
+
+
+/* This entire source file will be skipped if the application is not configured
+to include software timer functionality.  This #if is closed at the very bottom
+of this file.  If you want to include software timer functionality then ensure
+configUSE_TIMERS is set to 1 in FreeRTOSConfig.h. */
+#if ( configUSE_TIMERS == 1 )
+
+/* Misc definitions. */
+#define tmrNO_DELAY		( portTickType ) 0U
+
+/* The definition of the timers themselves. */
+typedef struct tmrTimerControl
+{
+	const signed char		*pcTimerName;		/*<< Text name.  This is not used by the kernel, it is included simply to make debugging easier. */
+	xListItem				xTimerListItem;		/*<< Standard linked list item as used by all kernel features for event management. */
+	portTickType			xTimerPeriodInTicks;/*<< How quickly and often the timer expires. */
+	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. */
+	void 					*pvTimerID;			/*<< An ID to identify the timer.  This allows the timer to be identified when the same callback is used for multiple timers. */
+	tmrTIMER_CALLBACK		pxCallbackFunction;	/*<< The function that will be called when the timer expires. */
+} xTIMER;
+
+/* The definition of messages that can be sent and received on the timer
+queue. */
+typedef struct tmrTimerQueueMessage
+{
+	portBASE_TYPE			xMessageID;			/*<< The command being sent to the timer service task. */
+	portTickType			xMessageValue;		/*<< An optional value used by a subset of commands, for example, when changing the period of a timer. */
+	xTIMER *				pxTimer;			/*<< The timer to which the command will be applied. */
+} xTIMER_MESSAGE;
+
+/*lint -e956 A manual analysis and inspection has been used to determine which
+static variables must be declared volatile. */
+
+/* The list in which active timers are stored.  Timers are referenced in expire
+time order, with the nearest expiry time at the front of the list.  Only the
+timer service task is allowed to access xActiveTimerList. */
+PRIVILEGED_DATA static xList xActiveTimerList1;
+PRIVILEGED_DATA static xList xActiveTimerList2;
+PRIVILEGED_DATA static xList *pxCurrentTimerList;
+PRIVILEGED_DATA static xList *pxOverflowTimerList;
+
+/* A queue that is used to send commands to the timer service task. */
+PRIVILEGED_DATA static xQueueHandle xTimerQueue = NULL;
+
+#if ( INCLUDE_xTimerGetTimerDaemonTaskHandle == 1 )
+
+	PRIVILEGED_DATA static xTaskHandle xTimerTaskHandle = NULL;
+
+#endif
+
+/*lint +e956 */
+
+/*-----------------------------------------------------------*/
+
+/*
+ * Initialise the infrastructure used by the timer service task if it has not
+ * been initialised already.
+ */
+static void prvCheckForValidListAndQueue( void ) PRIVILEGED_FUNCTION;
+
+/*
+ * The timer service task (daemon).  Timer functionality is controlled by this
+ * task.  Other tasks communicate with the timer service task using the
+ * xTimerQueue queue.
+ */
+static void prvTimerTask( void *pvParameters ) PRIVILEGED_FUNCTION;
+
+/*
+ * Called by the timer service task to interpret and process a command it
+ * received on the timer queue.
+ */
+static void	prvProcessReceivedCommands( void ) PRIVILEGED_FUNCTION;
+
+/*
+ * Insert the timer into either xActiveTimerList1, or xActiveTimerList2,
+ * depending on if the expire time causes a timer counter overflow.
+ */
+static portBASE_TYPE prvInsertTimerInActiveList( xTIMER *pxTimer, portTickType xNextExpiryTime, portTickType xTimeNow, portTickType xCommandTime ) PRIVILEGED_FUNCTION;
+
+/*
+ * An active timer has reached its expire time.  Reload the timer if it is an
+ * auto reload timer, then call its callback.
+ */
+static void prvProcessExpiredTimer( portTickType xNextExpireTime, portTickType xTimeNow ) PRIVILEGED_FUNCTION;
+
+/*
+ * The tick count has overflowed.  Switch the timer lists after ensuring the
+ * current timer list does not still reference some timers.
+ */
+static void prvSwitchTimerLists( portTickType xLastTime ) PRIVILEGED_FUNCTION;
+
+/*
+ * Obtain the current tick count, setting *pxTimerListsWereSwitched to pdTRUE
+ * if a tick count overflow occurred since prvSampleTimeNow() was last called.
+ */
+static portTickType prvSampleTimeNow( portBASE_TYPE *pxTimerListsWereSwitched ) PRIVILEGED_FUNCTION;
+
+/*
+ * If the timer list contains any active timers then return the expire time of
+ * the timer that will expire first and set *pxListWasEmpty to false.  If the
+ * timer list does not contain any timers then return 0 and set *pxListWasEmpty
+ * to pdTRUE.
+ */
+static portTickType prvGetNextExpireTime( portBASE_TYPE *pxListWasEmpty ) PRIVILEGED_FUNCTION;
+
+/*
+ * If a timer has expired, process it.  Otherwise, block the timer service task
+ * until either a timer does expire or a command is received.
+ */
+static void prvProcessTimerOrBlockTask( portTickType xNextExpireTime, portBASE_TYPE xListWasEmpty ) PRIVILEGED_FUNCTION;
+
+/*-----------------------------------------------------------*/
+
+portBASE_TYPE xTimerCreateTimerTask( void )
+{
+portBASE_TYPE xReturn = pdFAIL;
+
+	/* This function is called when the scheduler is started if
+	configUSE_TIMERS is set to 1.  Check that the infrastructure used by the
+	timer service task has been created/initialised.  If timers have already
+	been created then the initialisation will already have been performed. */
+	prvCheckForValidListAndQueue();
+
+	if( xTimerQueue != NULL )
+	{
+		#if ( INCLUDE_xTimerGetTimerDaemonTaskHandle == 1 )
+		{
+			/* Create the timer task, storing its handle in xTimerTaskHandle so
+			it can be returned by the xTimerGetTimerDaemonTaskHandle() function. */
+			xReturn = xTaskCreate( prvTimerTask, ( const signed char * ) "Tmr Svc", ( unsigned short ) configTIMER_TASK_STACK_DEPTH, NULL, ( ( unsigned portBASE_TYPE ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT, &xTimerTaskHandle );
+		}
+		#else
+		{
+			/* Create the timer task without storing its handle. */
+			xReturn = xTaskCreate( prvTimerTask, ( const signed char * ) "Tmr Svc", ( unsigned short ) configTIMER_TASK_STACK_DEPTH, NULL, ( ( unsigned portBASE_TYPE ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT, NULL);
+		}
+		#endif
+	}
+
+	configASSERT( xReturn );
+	return xReturn;
+}
+/*-----------------------------------------------------------*/
+
+xTimerHandle xTimerCreate( const signed char * const pcTimerName, portTickType xTimerPeriodInTicks, unsigned portBASE_TYPE uxAutoReload, void *pvTimerID, tmrTIMER_CALLBACK pxCallbackFunction )
+{
+xTIMER *pxNewTimer;
+
+	/* Allocate the timer structure. */
+	if( xTimerPeriodInTicks == ( portTickType ) 0U )
+	{
+		pxNewTimer = NULL;
+	}
+	else
+	{
+		pxNewTimer = ( xTIMER * ) pvPortMalloc( sizeof( xTIMER ) );
+		if( pxNewTimer != NULL )
+		{
+			/* Ensure the infrastructure used by the timer service task has been
+			created/initialised. */
+			prvCheckForValidListAndQueue();
+
+			/* Initialise the timer structure members using the function parameters. */
+			pxNewTimer->pcTimerName = pcTimerName;
+			pxNewTimer->xTimerPeriodInTicks = xTimerPeriodInTicks;
+			pxNewTimer->uxAutoReload = uxAutoReload;
+			pxNewTimer->pvTimerID = pvTimerID;
+			pxNewTimer->pxCallbackFunction = pxCallbackFunction;
+			vListInitialiseItem( &( pxNewTimer->xTimerListItem ) );
+
+			traceTIMER_CREATE( pxNewTimer );
+		}
+		else
+		{
+			traceTIMER_CREATE_FAILED();
+		}
+	}
+
+	/* 0 is not a valid value for xTimerPeriodInTicks. */
+	configASSERT( ( xTimerPeriodInTicks > 0 ) );
+
+	return ( xTimerHandle ) pxNewTimer;
+}
+/*-----------------------------------------------------------*/
+
+portBASE_TYPE xTimerGenericCommand( xTimerHandle xTimer, portBASE_TYPE xCommandID, portTickType xOptionalValue, signed portBASE_TYPE *pxHigherPriorityTaskWoken, portTickType xBlockTime )
+{
+portBASE_TYPE xReturn = pdFAIL;
+xTIMER_MESSAGE xMessage;
+
+	/* Send a message to the timer service task to perform a particular action
+	on a particular timer definition. */
+	if( xTimerQueue != NULL )
+	{
+		/* Send a command to the timer service task to start the xTimer timer. */
+		xMessage.xMessageID = xCommandID;
+		xMessage.xMessageValue = xOptionalValue;
+		xMessage.pxTimer = ( xTIMER * ) xTimer;
+
+		if( pxHigherPriorityTaskWoken == NULL )
+		{
+			if( xTaskGetSchedulerState() == taskSCHEDULER_RUNNING )
+			{
+				xReturn = xQueueSendToBack( xTimerQueue, &xMessage, xBlockTime );
+			}
+			else
+			{
+				xReturn = xQueueSendToBack( xTimerQueue, &xMessage, tmrNO_DELAY );
+			}
+		}
+		else
+		{
+			xReturn = xQueueSendToBackFromISR( xTimerQueue, &xMessage, pxHigherPriorityTaskWoken );
+		}
+
+		traceTIMER_COMMAND_SEND( xTimer, xCommandID, xOptionalValue, xReturn );
+	}
+
+	return xReturn;
+}
+/*-----------------------------------------------------------*/
+
+#if ( INCLUDE_xTimerGetTimerDaemonTaskHandle == 1 )
+
+	xTaskHandle xTimerGetTimerDaemonTaskHandle( void )
+	{
+		/* If xTimerGetTimerDaemonTaskHandle() is called before the scheduler has been
+		started, then xTimerTaskHandle will be NULL. */
+		configASSERT( ( xTimerTaskHandle != NULL ) );
+		return xTimerTaskHandle;
+	}
+
+#endif
+/*-----------------------------------------------------------*/
+
+static void prvProcessExpiredTimer( portTickType xNextExpireTime, portTickType xTimeNow )
+{
+xTIMER *pxTimer;
+portBASE_TYPE xResult;
+
+	/* Remove the timer from the list of active timers.  A check has already
+	been performed to ensure the list is not empty. */
+	pxTimer = ( xTIMER * ) listGET_OWNER_OF_HEAD_ENTRY( pxCurrentTimerList );
+	( void ) uxListRemove( &( pxTimer->xTimerListItem ) );
+	traceTIMER_EXPIRED( pxTimer );
+
+	/* If the timer is an auto reload timer then calculate the next
+	expiry time and re-insert the timer in the list of active timers. */
+	if( pxTimer->uxAutoReload == ( unsigned portBASE_TYPE ) pdTRUE )
+	{
+		/* This is the only time a timer is inserted into a list using
+		a time relative to anything other than the current time.  It
+		will therefore be inserted into the correct list relative to
+		the time this task thinks it is now, even if a command to
+		switch lists due to a tick count overflow is already waiting in
+		the timer queue. */
+		if( prvInsertTimerInActiveList( pxTimer, ( xNextExpireTime + pxTimer->xTimerPeriodInTicks ), xTimeNow, xNextExpireTime ) == pdTRUE )
+		{
+			/* The timer expired before it was added to the active timer
+			list.  Reload it now.  */
+			xResult = xTimerGenericCommand( pxTimer, tmrCOMMAND_START, xNextExpireTime, NULL, tmrNO_DELAY );
+			configASSERT( xResult );
+			( void ) xResult;
+		}
+	}
+
+	/* Call the timer callback. */
+	pxTimer->pxCallbackFunction( ( xTimerHandle ) pxTimer );
+}
+/*-----------------------------------------------------------*/
+
+static void prvTimerTask( void *pvParameters )
+{
+portTickType xNextExpireTime;
+portBASE_TYPE xListWasEmpty;
+
+	/* Just to avoid compiler warnings. */
+	( void ) pvParameters;
+
+	for( ;; )
+	{
+		/* Query the timers list to see if it contains any timers, and if so,
+		obtain the time at which the next timer will expire. */
+		xNextExpireTime = prvGetNextExpireTime( &xListWasEmpty );
+
+		/* If a timer has expired, process it.  Otherwise, block this task
+		until either a timer does expire, or a command is received. */
+		prvProcessTimerOrBlockTask( xNextExpireTime, xListWasEmpty );
+
+		/* Empty the command queue. */
+		prvProcessReceivedCommands();
+	}
+}
+/*-----------------------------------------------------------*/
+
+static void prvProcessTimerOrBlockTask( portTickType xNextExpireTime, portBASE_TYPE xListWasEmpty )
+{
+portTickType xTimeNow;
+portBASE_TYPE xTimerListsWereSwitched;
+
+	vTaskSuspendAll();
+	{
+		/* Obtain the time now to make an assessment as to whether the timer
+		has expired or not.  If obtaining the time causes the lists to switch
+		then don't process this timer as any timers that remained in the list
+		when the lists were switched will have been processed within the
+		prvSampelTimeNow() function. */
+		xTimeNow = prvSampleTimeNow( &xTimerListsWereSwitched );
+		if( xTimerListsWereSwitched == pdFALSE )
+		{
+			/* The tick count has not overflowed, has the timer expired? */
+			if( ( xListWasEmpty == pdFALSE ) && ( xNextExpireTime <= xTimeNow ) )
+			{
+				( void ) xTaskResumeAll();
+				prvProcessExpiredTimer( xNextExpireTime, xTimeNow );
+			}
+			else
+			{
+				/* The tick count has not overflowed, and the next expire
+				time has not been reached yet.  This task should therefore
+				block to wait for the next expire time or a command to be
+				received - whichever comes first.  The following line cannot
+				be reached unless xNextExpireTime > xTimeNow, except in the
+				case when the current timer list is empty. */
+				vQueueWaitForMessageRestricted( xTimerQueue, ( xNextExpireTime - xTimeNow ) );
+
+				if( xTaskResumeAll() == pdFALSE )
+				{
+					/* Yield to wait for either a command to arrive, or the block time
+					to expire.  If a command arrived between the critical section being
+					exited and this yield then the yield will not cause the task
+					to block. */
+					portYIELD_WITHIN_API();
+				}
+			}
+		}
+		else
+		{
+			( void ) xTaskResumeAll();
+		}
+	}
+}
+/*-----------------------------------------------------------*/
+
+static portTickType prvGetNextExpireTime( portBASE_TYPE *pxListWasEmpty )
+{
+portTickType xNextExpireTime;
+
+	/* Timers are listed in expiry time order, with the head of the list
+	referencing the task that will expire first.  Obtain the time at which
+	the timer with the nearest expiry time will expire.  If there are no
+	active timers then just set the next expire time to 0.  That will cause
+	this task to unblock when the tick count overflows, at which point the
+	timer lists will be switched and the next expiry time can be
+	re-assessed.  */
+	*pxListWasEmpty = listLIST_IS_EMPTY( pxCurrentTimerList );
+	if( *pxListWasEmpty == pdFALSE )
+	{
+		xNextExpireTime = listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxCurrentTimerList );
+	}
+	else
+	{
+		/* Ensure the task unblocks when the tick count rolls over. */
+		xNextExpireTime = ( portTickType ) 0U;
+	}
+
+	return xNextExpireTime;
+}
+/*-----------------------------------------------------------*/
+
+static portTickType prvSampleTimeNow( portBASE_TYPE *pxTimerListsWereSwitched )
+{
+portTickType xTimeNow;
+PRIVILEGED_DATA static portTickType xLastTime = ( portTickType ) 0U; /*lint !e956 Variable is only accessible to one task. */
+
+	xTimeNow = xTaskGetTickCount();
+
+	if( xTimeNow < xLastTime )
+	{
+		prvSwitchTimerLists( xLastTime );
+		*pxTimerListsWereSwitched = pdTRUE;
+	}
+	else
+	{
+		*pxTimerListsWereSwitched = pdFALSE;
+	}
+
+	xLastTime = xTimeNow;
+
+	return xTimeNow;
+}
+/*-----------------------------------------------------------*/
+
+static portBASE_TYPE prvInsertTimerInActiveList( xTIMER *pxTimer, portTickType xNextExpiryTime, portTickType xTimeNow, portTickType xCommandTime )
+{
+portBASE_TYPE xProcessTimerNow = pdFALSE;
+
+	listSET_LIST_ITEM_VALUE( &( pxTimer->xTimerListItem ), xNextExpiryTime );
+	listSET_LIST_ITEM_OWNER( &( pxTimer->xTimerListItem ), pxTimer );
+
+	if( xNextExpiryTime <= xTimeNow )
+	{
+		/* Has the expiry time elapsed between the command to start/reset a
+		timer was issued, and the time the command was processed? */
+		if( ( xTimeNow - xCommandTime ) >= pxTimer->xTimerPeriodInTicks )
+		{
+			/* The time between a command being issued and the command being
+			processed actually exceeds the timers period.  */
+			xProcessTimerNow = pdTRUE;
+		}
+		else
+		{
+			vListInsert( pxOverflowTimerList, &( pxTimer->xTimerListItem ) );
+		}
+	}
+	else
+	{
+		if( ( xTimeNow < xCommandTime ) && ( xNextExpiryTime >= xCommandTime ) )
+		{
+			/* If, since the command was issued, the tick count has overflowed
+			but the expiry time has not, then the timer must have already passed
+			its expiry time and should be processed immediately. */
+			xProcessTimerNow = pdTRUE;
+		}
+		else
+		{
+			vListInsert( pxCurrentTimerList, &( pxTimer->xTimerListItem ) );
+		}
+	}
+
+	return xProcessTimerNow;
+}
+/*-----------------------------------------------------------*/
+
+static void	prvProcessReceivedCommands( void )
+{
+xTIMER_MESSAGE xMessage;
+xTIMER *pxTimer;
+portBASE_TYPE xTimerListsWereSwitched, xResult;
+portTickType xTimeNow;
+
+	while( xQueueReceive( xTimerQueue, &xMessage, tmrNO_DELAY ) != pdFAIL ) /*lint !e603 xMessage does not have to be initialised as it is passed out, not in, and it is not used unless xQueueReceive() returns pdTRUE. */
+	{
+		pxTimer = xMessage.pxTimer;
+
+		if( listIS_CONTAINED_WITHIN( NULL, &( pxTimer->xTimerListItem ) ) == pdFALSE )
+		{
+			/* The timer is in a list, remove it. */
+			( void ) uxListRemove( &( pxTimer->xTimerListItem ) );
+		}
+
+		traceTIMER_COMMAND_RECEIVED( pxTimer, xMessage.xMessageID, xMessage.xMessageValue );
+
+		/* In this case the xTimerListsWereSwitched parameter is not used, but 
+		it must be present in the function call.  prvSampleTimeNow() must be 
+		called after the message is received from xTimerQueue so there is no 
+		possibility of a higher priority task adding a message to the message
+		queue with a time that is ahead of the timer daemon task (because it
+		pre-empted the timer daemon task after the xTimeNow value was set). */
+		xTimeNow = prvSampleTimeNow( &xTimerListsWereSwitched );
+
+		switch( xMessage.xMessageID )
+		{
+			case tmrCOMMAND_START :
+				/* Start or restart a timer. */
+				if( prvInsertTimerInActiveList( pxTimer,  xMessage.xMessageValue + pxTimer->xTimerPeriodInTicks, xTimeNow, xMessage.xMessageValue ) == pdTRUE )
+				{
+					/* The timer expired before it was added to the active timer
+					list.  Process it now. */
+					pxTimer->pxCallbackFunction( ( xTimerHandle ) pxTimer );
+
+					if( pxTimer->uxAutoReload == ( unsigned portBASE_TYPE ) pdTRUE )
+					{
+						xResult = xTimerGenericCommand( pxTimer, tmrCOMMAND_START, xMessage.xMessageValue + pxTimer->xTimerPeriodInTicks, NULL, tmrNO_DELAY );
+						configASSERT( xResult );
+						( void ) xResult;
+					}
+				}
+				break;
+
+			case tmrCOMMAND_STOP :
+				/* The timer has already been removed from the active list.
+				There is nothing to do here. */
+				break;
+
+			case tmrCOMMAND_CHANGE_PERIOD :
+				pxTimer->xTimerPeriodInTicks = xMessage.xMessageValue;
+				configASSERT( ( pxTimer->xTimerPeriodInTicks > 0 ) );
+
+				/* The new period does not really have a reference, and can be
+				longer or shorter than the old one.  The command time is 
+				therefore set to the current time, and as the period cannot be
+				zero the next expiry time can only be in the future, meaning
+				(unlike for the xTimerStart() case above) there is no fail case
+				that needs to be handled here. */
+				( void ) prvInsertTimerInActiveList( pxTimer, ( xTimeNow + pxTimer->xTimerPeriodInTicks ), xTimeNow, xTimeNow );
+				break;
+
+			case tmrCOMMAND_DELETE :
+				/* The timer has already been removed from the active list,
+				just free up the memory. */
+				vPortFree( pxTimer );
+				break;
+
+			default	:
+				/* Don't expect to get here. */
+				break;
+		}
+	}
+}
+/*-----------------------------------------------------------*/
+
+static void prvSwitchTimerLists( portTickType xLastTime )
+{
+portTickType xNextExpireTime, xReloadTime;
+xList *pxTemp;
+xTIMER *pxTimer;
+portBASE_TYPE xResult;
+
+	/* Remove compiler warnings if configASSERT() is not defined. */
+	( void ) xLastTime;
+
+	/* The tick count has overflowed.  The timer lists must be switched.
+	If there are any timers still referenced from the current timer list
+	then they must have expired and should be processed before the lists
+	are switched. */
+	while( listLIST_IS_EMPTY( pxCurrentTimerList ) == pdFALSE )
+	{
+		xNextExpireTime = listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxCurrentTimerList );
+
+		/* Remove the timer from the list. */
+		pxTimer = ( xTIMER * ) listGET_OWNER_OF_HEAD_ENTRY( pxCurrentTimerList );
+		( void ) uxListRemove( &( pxTimer->xTimerListItem ) );
+
+		/* Execute its callback, then send a command to restart the timer if
+		it is an auto-reload timer.  It cannot be restarted here as the lists
+		have not yet been switched. */
+		pxTimer->pxCallbackFunction( ( xTimerHandle ) pxTimer );
+
+		if( pxTimer->uxAutoReload == ( unsigned portBASE_TYPE ) pdTRUE )
+		{
+			/* Calculate the reload value, and if the reload value results in
+			the timer going into the same timer list then it has already expired
+			and the timer should be re-inserted into the current list so it is
+			processed again within this loop.  Otherwise a command should be sent
+			to restart the timer to ensure it is only inserted into a list after
+			the lists have been swapped. */
+			xReloadTime = ( xNextExpireTime + pxTimer->xTimerPeriodInTicks );
+			if( xReloadTime > xNextExpireTime )
+			{
+				listSET_LIST_ITEM_VALUE( &( pxTimer->xTimerListItem ), xReloadTime );
+				listSET_LIST_ITEM_OWNER( &( pxTimer->xTimerListItem ), pxTimer );
+				vListInsert( pxCurrentTimerList, &( pxTimer->xTimerListItem ) );
+			}
+			else
+			{
+				xResult = xTimerGenericCommand( pxTimer, tmrCOMMAND_START, xNextExpireTime, NULL, tmrNO_DELAY );
+				configASSERT( xResult );
+				( void ) xResult;
+			}
+		}
+	}
+
+	pxTemp = pxCurrentTimerList;
+	pxCurrentTimerList = pxOverflowTimerList;
+	pxOverflowTimerList = pxTemp;
+}
+/*-----------------------------------------------------------*/
+
+static void prvCheckForValidListAndQueue( void )
+{
+	/* Check that the list from which active timers are referenced, and the
+	queue used to communicate with the timer service, have been
+	initialised. */
+	taskENTER_CRITICAL();
+	{
+		if( xTimerQueue == NULL )
+		{
+			vListInitialise( &xActiveTimerList1 );
+			vListInitialise( &xActiveTimerList2 );
+			pxCurrentTimerList = &xActiveTimerList1;
+			pxOverflowTimerList = &xActiveTimerList2;
+			xTimerQueue = xQueueCreate( ( unsigned portBASE_TYPE ) configTIMER_QUEUE_LENGTH, sizeof( xTIMER_MESSAGE ) );
+		}
+	}
+	taskEXIT_CRITICAL();
+}
+/*-----------------------------------------------------------*/
+
+portBASE_TYPE xTimerIsTimerActive( xTimerHandle xTimer )
+{
+portBASE_TYPE xTimerIsInActiveList;
+xTIMER *pxTimer = ( xTIMER * ) xTimer;
+
+	/* Is the timer in the list of active timers? */
+	taskENTER_CRITICAL();
+	{
+		/* Checking to see if it is in the NULL list in effect checks to see if
+		it is referenced from either the current or the overflow timer lists in
+		one go, but the logic has to be reversed, hence the '!'. */
+		xTimerIsInActiveList = !( listIS_CONTAINED_WITHIN( NULL, &( pxTimer->xTimerListItem ) ) );
+	}
+	taskEXIT_CRITICAL();
+
+	return xTimerIsInActiveList;
+}
+/*-----------------------------------------------------------*/
+
+void *pvTimerGetTimerID( xTimerHandle xTimer )
+{
+xTIMER *pxTimer = ( xTIMER * ) xTimer;
+
+	return pxTimer->pvTimerID;
+}
+/*-----------------------------------------------------------*/
+
+/* This entire source file will be skipped if the application is not configured
+to include software timer functionality.  If you want to include software timer
+functionality then ensure configUSE_TIMERS is set to 1 in FreeRTOSConfig.h. */
+#endif /* configUSE_TIMERS == 1 */
+
+
+