好记性不如铅笔头

ARM, FreeRTOS, 操作系统

FreeRTOS代码阅读笔记:Timers.c

最近忙成狗了,简单的笔记下吧。

Timer是freertos内部实现的一个软件定时器,通过一个守护task来进行管理。代码比较简单,而且freertos的注释非常详细,这里简单的笔记了一小部分代码。

Timers.c:

/* 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"

#if ( INCLUDE_xTimerPendFunctionCall == 1 ) && ( configUSE_TIMERS == 0 )
	#error configUSE_TIMERS must be set to 1 to make the xTimerPendFunctionCall() function available.
#endif

/* 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		( TickType_t ) 0U

/* The definition of the timers themselves. */
typedef struct tmrTimerControl
{
	const char				*pcTimerName;		/*<< Text name.  This is not used by the kernel, it is included simply to make debugging easier. */ /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
	ListItem_t				xTimerListItem;		/*<< Standard linked list item as used by all kernel features for event management. */
	TickType_t				xTimerPeriodInTicks;/*<< How quickly and often the timer expires. */
	UBaseType_t				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. */
	TimerCallbackFunction_t	pxCallbackFunction;	/*<< The function that will be called when the timer expires. */
	#if( configUSE_TRACE_FACILITY == 1 )
		UBaseType_t			uxTimerNumber;		/*<< An ID assigned by trace tools such as FreeRTOS+Trace */
	#endif
} xTIMER;

/* The old xTIMER name is maintained above then typedefed to the new Timer_t
name below to enable the use of older kernel aware debuggers. */
typedef xTIMER Timer_t;

/* The definition of messages that can be sent and received on the timer queue.
Two types of message can be queued - messages that manipulate a software timer,
and messages that request the execution of a non-timer related callback.  The
two message types are defined in two separate structures, xTimerParametersType
and xCallbackParametersType respectively. */
typedef struct tmrTimerParameters
{
	TickType_t			xMessageValue;		/*<< An optional value used by a subset of commands, for example, when changing the period of a timer. */
	Timer_t *			pxTimer;			/*<< The timer to which the command will be applied. */
} TimerParameter_t;


typedef struct tmrCallbackParameters
{
	PendedFunction_t	pxCallbackFunction;	/* << The callback function to execute. */
	void *pvParameter1;						/* << The value that will be used as the callback functions first parameter. */
	uint32_t ulParameter2;					/* << The value that will be used as the callback functions second parameter. */
} CallbackParameters_t;

/* The structure that contains the two message types, along with an identifier
that is used to determine which message type is valid. */
typedef struct tmrTimerQueueMessage
{
	BaseType_t			xMessageID;			/*<< The command being sent to the timer service task. */
	union
	{
		TimerParameter_t xTimerParameters;

		/* Don't include xCallbackParameters if it is not going to be used as
		it makes the structure (and therefore the timer queue) larger. */
		#if ( INCLUDE_xTimerPendFunctionCall == 1 )
			CallbackParameters_t xCallbackParameters;
		#endif /* INCLUDE_xTimerPendFunctionCall */
	} u;
} DaemonTaskMessage_t;

/*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 these lists. */
PRIVILEGED_DATA static List_t xActiveTimerList1;
PRIVILEGED_DATA static List_t xActiveTimerList2;
PRIVILEGED_DATA static List_t *pxCurrentTimerList;
PRIVILEGED_DATA static List_t *pxOverflowTimerList;

/* A queue that is used to send commands to the timer service task. */
PRIVILEGED_DATA static QueueHandle_t xTimerQueue = NULL;

#if ( INCLUDE_xTimerGetTimerDaemonTaskHandle == 1 )

	PRIVILEGED_DATA static TaskHandle_t 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 BaseType_t prvInsertTimerInActiveList( Timer_t * const pxTimer, const TickType_t xNextExpiryTime, const TickType_t xTimeNow, const TickType_t 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( const TickType_t xNextExpireTime, const TickType_t 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( void ) PRIVILEGED_FUNCTION;

/*
 * Obtain the current tick count, setting *pxTimerListsWereSwitched to pdTRUE
 * if a tick count overflow occurred since prvSampleTimeNow() was last called.
 */
static TickType_t prvSampleTimeNow( BaseType_t * const 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 TickType_t prvGetNextExpireTime( BaseType_t * const 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( const TickType_t xNextExpireTime, const BaseType_t xListWasEmpty ) PRIVILEGED_FUNCTION;

/*-----------------------------------------------------------*/


/*
创建一个task,内部的实现函数就是软件定时器内部的管理函数。
调用出代码 :
void vTaskStartScheduler( void )
{
BaseType_t xReturn;
。。。。。。
	#if ( configUSE_TIMERS == 1 )
	{
		if( xReturn == pdPASS )
		{
			xReturn = xTimerCreateTimerTask();
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}
	#endif
}

*/
BaseType_t xTimerCreateTimerTask( void )
{
BaseType_t 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, "Tmr Svc", ( uint16_t ) configTIMER_TASK_STACK_DEPTH, NULL, ( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT, &xTimerTaskHandle );
		}
		#else
		{
			/* Create the timer task without storing its handle. */
			xReturn = xTaskCreate( prvTimerTask, "Tmr Svc", ( uint16_t ) configTIMER_TASK_STACK_DEPTH, NULL, ( ( UBaseType_t ) configTIMER_TASK_PRIORITY ) | portPRIVILEGE_BIT, NULL);
		}
		#endif
	}
	else
	{
		mtCOVERAGE_TEST_MARKER();
	}

	configASSERT( xReturn );
	return xReturn;
}
/*-----------------------------------------------------------*/

 /* 注册一个软件定时器,返回注册的定时器的句柄
注意这里的pvTimerID是一个void*,因此可以传送一个结构体指针神马的,方便回调函数获取。
 */
TimerHandle_t xTimerCreate( const char * const pcTimerName, const TickType_t xTimerPeriodInTicks, const UBaseType_t uxAutoReload, void * const pvTimerID, TimerCallbackFunction_t pxCallbackFunction ) /*lint !e971 Unqualified char types are allowed for strings and single characters only. */
{
Timer_t *pxNewTimer;

	/* Allocate the timer structure. */
	if( xTimerPeriodInTicks == ( TickType_t ) 0U )
	{
		pxNewTimer = NULL;
	}
	else
	{	/* 为这个软件定时器申请一块内存 */
		pxNewTimer = ( Timer_t * ) pvPortMalloc( sizeof( Timer_t ) );
		if( pxNewTimer != NULL )
		{
			/* Ensure the infrastructure used by the timer service task has been
			created/initialised. */
			prvCheckForValidListAndQueue();

			/* 初始化软件定时器结构体 */
			/* 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 ) );

	/* 注意这里返回的handler其实就是申请的内存指针,也就是Timer_t *  */
	return ( TimerHandle_t ) pxNewTimer;
}
/*-----------------------------------------------------------*/
/*
内部工具函数,用来统一管理对软件定时器的命令。
这里采用的是命令队列的操作,命令会被封装后放入命令队列。
但是这里并不会对命令进行处理,命令的处理是守护 task的工作。
这样做的好处是简化处理:软件定时器是由守护task进行模拟的,
假如有一个软件定时器要被修改状态(启动,停止),函数调用后
不会立即生效,只有守护task被调度后才会生效。
*/
BaseType_t xTimerGenericCommand( TimerHandle_t xTimer, const BaseType_t xCommandID, const TickType_t xOptionalValue, BaseType_t * const pxHigherPriorityTaskWoken, const TickType_t xTicksToWait )
{
BaseType_t xReturn = pdFAIL;
DaemonTaskMessage_t 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.u.xTimerParameters.xMessageValue = xOptionalValue;
		xMessage.u.xTimerParameters.pxTimer = ( Timer_t * ) xTimer;

		if( xCommandID < tmrFIRST_FROM_ISR_COMMAND )
		{
			if( xTaskGetSchedulerState() == taskSCHEDULER_RUNNING )
			{
				xReturn = xQueueSendToBack( xTimerQueue, &xMessage, xTicksToWait );
			}
			else
			{
				xReturn = xQueueSendToBack( xTimerQueue, &xMessage, tmrNO_DELAY );
			}
		}
		else
		{
			xReturn = xQueueSendToBackFromISR( xTimerQueue, &xMessage, pxHigherPriorityTaskWoken );
		}

		traceTIMER_COMMAND_SEND( xTimer, xCommandID, xOptionalValue, xReturn );
	}
	else
	{
		mtCOVERAGE_TEST_MARKER();
	}

	return xReturn;
}
/*-----------------------------------------------------------*/

 /*
返回软件定时器后面的守护task。
因为定时器是软件模拟的,因此必定后面有一个task在不停的轮询
注册的软件定时器。
*/
#if ( INCLUDE_xTimerGetTimerDaemonTaskHandle == 1 )

	TaskHandle_t xTimerGetTimerDaemonTaskHandle( void )
	{
		/* If xTimerGetTimerDaemonTaskHandle() is called before the scheduler has been
		started, then xTimerTaskHandle will be NULL. */
		configASSERT( ( xTimerTaskHandle != NULL ) );
		return xTimerTaskHandle;
	}

#endif
/*-----------------------------------------------------------*/

const char * pcTimerGetTimerName( TimerHandle_t xTimer )
{
Timer_t *pxTimer = ( Timer_t * ) xTimer;

	return pxTimer->pcTimerName;
}
/*-----------------------------------------------------------*/

static void prvProcessExpiredTimer( const TickType_t xNextExpireTime, const TickType_t xTimeNow )
{
BaseType_t xResult;
Timer_t * const pxTimer = ( Timer_t * ) listGET_OWNER_OF_HEAD_ENTRY( pxCurrentTimerList );

	/* Remove the timer from the list of active timers.  A check has already
	been performed to ensure the list is not empty. */
	( 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 == ( UBaseType_t ) pdTRUE )
	{
		/* The 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. */
		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_DONT_TRACE, xNextExpireTime, NULL, tmrNO_DELAY );
			configASSERT( xResult );
			( void ) xResult;
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}
	else
	{
		mtCOVERAGE_TEST_MARKER();
	}

	/* Call the timer callback. */
	pxTimer->pxCallbackFunction( ( TimerHandle_t ) pxTimer );
}
/*-----------------------------------------------------------*/



/*软件定时器守护task的实现函数。*/
static void prvTimerTask( void *pvParameters )
{
TickType_t xNextExpireTime;
BaseType_t xListWasEmpty;

	/* Just to avoid compiler warnings. */
	( void ) pvParameters;

/*
守护函数很简单,获取下一个软件定时器,
如果这个软件定时器到期了,就执行它,否则就阻塞自己,
直到这个软件定时器到期。

*/

	for( ;; )
	{
	/* 获取下一个要到期的软件定时器的时间 */
		/* 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( const TickType_t xNextExpireTime, const BaseType_t xListWasEmpty )
{
TickType_t xTimeNow;
BaseType_t 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
		prvSampleTimeNow() function. */
		xTimeNow = prvSampleTimeNow( &xTimerListsWereSwitched );
		if( xTimerListsWereSwitched == pdFALSE )
		{
			/* tick没有溢出而且定时器链表中还有定时器而且当前时间已经到了
				定时器的预定时间 ,那么就响应该定时器
			*/
			/* The tick count has not overflowed, has the timer expired? */
			if( ( xListWasEmpty == pdFALSE ) && ( xNextExpireTime <= xTimeNow ) )
			{
				( void ) xTaskResumeAll();
				prvProcessExpiredTimer( xNextExpireTime, xTimeNow );
			}
			else
			{
			/* 如果定时器的时间没有到,那么就阻塞当前的task */
			
				/* 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. */
			/* 当前task在QUEUE	上进行阻塞,阻塞时间 ( xNextExpireTime - xTimeNow ) 后会被
			唤醒或者queue被修改也会被唤醒。	
			*/
				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
				{
					mtCOVERAGE_TEST_MARKER();
				}
			}
		}
		else
		{
			( void ) xTaskResumeAll();
		}
	}
}
/*-----------------------------------------------------------*/

static TickType_t prvGetNextExpireTime( BaseType_t * const pxListWasEmpty )
{
TickType_t 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.  */
	/* 定时器是根据下一次到期时间插入到链表中的,因此
	    链表的第一个定时器就是第一个要到期的。
	*/


	/* 先记录下定时器链表是否为空 */
	*pxListWasEmpty = listLIST_IS_EMPTY( pxCurrentTimerList );
	if( *pxListWasEmpty == pdFALSE )
	{
		/* 获取第一个要到期的定时器的时间 */
		xNextExpireTime = listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxCurrentTimerList );
	}
	else
	{
		/* Ensure the task unblocks when the tick count rolls over. */
		xNextExpireTime = ( TickType_t ) 0U;
	}

	return xNextExpireTime;
}
/*-----------------------------------------------------------*/


static TickType_t prvSampleTimeNow( BaseType_t * const pxTimerListsWereSwitched )
{
TickType_t xTimeNow;
PRIVILEGED_DATA static TickType_t xLastTime = ( TickType_t ) 0U; /*lint !e956 Variable is only accessible to one task. */

	/* 获取当前的tick计数  */
	xTimeNow = xTaskGetTickCount();

	/* 如果当前的tick计数反而小于上次记录的值,那么说明tick
		溢出了,那么据需要切换队列。
	*/
	if( xTimeNow < xLastTime )
	{
		prvSwitchTimerLists();
		*pxTimerListsWereSwitched = pdTRUE;
	}
	else
	{
		*pxTimerListsWereSwitched = pdFALSE;
	}

	/* 将当前的tick记录下来 */
	xLastTime = xTimeNow;

	return xTimeNow;
}
/*-----------------------------------------------------------*/

static BaseType_t prvInsertTimerInActiveList( Timer_t * const pxTimer, const TickType_t xNextExpiryTime, const TickType_t xTimeNow, const TickType_t xCommandTime )
{
BaseType_t 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;
}
/*-----------------------------------------------------------*/

/*
从命令队列中取出命令并进行处理。
*/
static void	prvProcessReceivedCommands( void )
{
DaemonTaskMessage_t xMessage;
Timer_t *pxTimer;
BaseType_t xTimerListsWereSwitched, xResult;
TickType_t 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. */
	{
		#if ( INCLUDE_xTimerPendFunctionCall == 1 )
		{
			/* Negative commands are pended function calls rather than timer
			commands. */
			if( xMessage.xMessageID < ( BaseType_t ) 0 )
			{
				const CallbackParameters_t * const pxCallback = &( xMessage.u.xCallbackParameters );

				/* The timer uses the xCallbackParameters member to request a
				callback be executed.  Check the callback is not NULL. */
				configASSERT( pxCallback );

				/* Call the function. */
				pxCallback->pxCallbackFunction( pxCallback->pvParameter1, pxCallback->ulParameter2 );
			}
			else
			{
				mtCOVERAGE_TEST_MARKER();
			}
		}
		#endif /* INCLUDE_xTimerPendFunctionCall */

		/* Commands that are positive are timer commands rather than pended
		function calls. */
		if( xMessage.xMessageID >= ( BaseType_t ) 0 )
		{
			/* The messages uses the xTimerParameters member to work on a
			software timer. */
			pxTimer = xMessage.u.xTimerParameters.pxTimer;

			if( listIS_CONTAINED_WITHIN( NULL, &( pxTimer->xTimerListItem ) ) == pdFALSE )
			{
				/* The timer is in a list, remove it. */
				( void ) uxListRemove( &( pxTimer->xTimerListItem ) );
			}
			else
			{
				mtCOVERAGE_TEST_MARKER();
			}

			traceTIMER_COMMAND_RECEIVED( pxTimer, xMessage.xMessageID, xMessage.u.xTimerParameters.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 :
			    case tmrCOMMAND_START_FROM_ISR :
			    case tmrCOMMAND_RESET :
			    case tmrCOMMAND_RESET_FROM_ISR :
				case tmrCOMMAND_START_DONT_TRACE :
					/* Start or restart a timer. */
					if( prvInsertTimerInActiveList( pxTimer,  xMessage.u.xTimerParameters.xMessageValue + pxTimer->xTimerPeriodInTicks, xTimeNow, xMessage.u.xTimerParameters.xMessageValue ) == pdTRUE )
					{
						/* The timer expired before it was added to the active
						timer list.  Process it now. */
						pxTimer->pxCallbackFunction( ( TimerHandle_t ) pxTimer );
						traceTIMER_EXPIRED( pxTimer );

						if( pxTimer->uxAutoReload == ( UBaseType_t ) pdTRUE )
						{
							xResult = xTimerGenericCommand( pxTimer, tmrCOMMAND_START_DONT_TRACE, xMessage.u.xTimerParameters.xMessageValue + pxTimer->xTimerPeriodInTicks, NULL, tmrNO_DELAY );
							configASSERT( xResult );
							( void ) xResult;
						}
						else
						{
							mtCOVERAGE_TEST_MARKER();
						}
					}
					else
					{
						mtCOVERAGE_TEST_MARKER();
					}
					break;

				case tmrCOMMAND_STOP :
				case tmrCOMMAND_STOP_FROM_ISR :
					/* The timer has already been removed from the active list.
					There is nothing to do here. */
					break;

				case tmrCOMMAND_CHANGE_PERIOD :
				case tmrCOMMAND_CHANGE_PERIOD_FROM_ISR :
					pxTimer->xTimerPeriodInTicks = xMessage.u.xTimerParameters.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;
			}
		}
	}
}
/*-----------------------------------------------------------*/


/* 切换定时器链表  */
static void prvSwitchTimerLists( void )
{
TickType_t xNextExpireTime, xReloadTime;
List_t *pxTemp;
Timer_t *pxTimer;
BaseType_t xResult;

	/* 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. */
	/* 
	由于外部的tick已经溢出了,因此这里需要切换定时器链表。
	pxCurrentTimerList在正常的情况下是不能有内容的,而这里就是处理
	pxCurrentTimerList里剩余的定时器,这里的做法是尽快的让这些定时器
	响应。如果有的定时器是自动重载的,而且在tick溢出前可以被
	执行多次,那么就多次响应它,即使响应间隔非常短。
	*/
	

	/*	如果当前的链表中还有没到期的定时器,删除它,并且
	执行它的回调函数(个人认为这里有点问题,或者定时器
	的最大定时时间是有限制的。)。
	出现这种情况的一个可能的原因就是TASK调度被延误了,导致
	很多软件定时器晚于预定期的时间。
	*/
	
	while( listLIST_IS_EMPTY( pxCurrentTimerList ) == pdFALSE )
	{
		xNextExpireTime = listGET_ITEM_VALUE_OF_HEAD_ENTRY( pxCurrentTimerList );

		/* Remove the timer from the list. */
		pxTimer = ( Timer_t * ) listGET_OWNER_OF_HEAD_ENTRY( pxCurrentTimerList );
		( void ) uxListRemove( &( pxTimer->xTimerListItem ) );
		traceTIMER_EXPIRED( pxTimer );

		/* 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( ( TimerHandle_t ) pxTimer );

		if( pxTimer->uxAutoReload == ( UBaseType_t ) 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. */
			/*
			如果一个软件定时器是自动重载的,而且下次到期的时间
			仍然没有溢出,就再次把它放到链表中,这样就会导致该定时器
			在很短的时间内被再次响应。
			*/			
			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_DONT_TRACE, xNextExpireTime, NULL, tmrNO_DELAY );
				configASSERT( xResult );
				( void ) xResult;
			}
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}

	pxTemp = pxCurrentTimerList;
	pxCurrentTimerList = pxOverflowTimerList;
	pxOverflowTimerList = pxTemp;
}
/*-----------------------------------------------------------*/

/*
教研下管理软件定时器的QUEUE是否已经初始化了
*/
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();
	{/* 如果queue没有初始化,就初始化这个QUEUE */
		if( xTimerQueue == NULL )
		{
			vListInitialise( &xActiveTimerList1 );
			vListInitialise( &xActiveTimerList2 );
			pxCurrentTimerList = &xActiveTimerList1;
			pxOverflowTimerList = &xActiveTimerList2;
			xTimerQueue = xQueueCreate( ( UBaseType_t ) configTIMER_QUEUE_LENGTH, sizeof( DaemonTaskMessage_t ) );
			configASSERT( xTimerQueue );

			#if ( configQUEUE_REGISTRY_SIZE > 0 )
			{
				if( xTimerQueue != NULL )
				{
					vQueueAddToRegistry( xTimerQueue, "TmrQ" );
				}
				else
				{
					mtCOVERAGE_TEST_MARKER();
				}
			}
			#endif /* configQUEUE_REGISTRY_SIZE */
		}
		else
		{
			mtCOVERAGE_TEST_MARKER();
		}
	}
	taskEXIT_CRITICAL();
}
/*-----------------------------------------------------------*/
/*
判断一个定时器是否处于活跃状态。
*/
BaseType_t xTimerIsTimerActive( TimerHandle_t xTimer )
{
BaseType_t xTimerIsInActiveList;
Timer_t *pxTimer = ( Timer_t * ) xTimer;
	/* 这里的判断方式很简单,看下这个软件定时器是否被添加到定时器链表中 就可以了*/


	/* 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 = ( BaseType_t ) !( listIS_CONTAINED_WITHIN( NULL, &( pxTimer->xTimerListItem ) ) );
	}
	taskEXIT_CRITICAL();

	return xTimerIsInActiveList;
} /*lint !e818 Can't be pointer to const due to the typedef. */
/*-----------------------------------------------------------*/

 /*  返回软件定时器的pvTimerID */
void *pvTimerGetTimerID( const TimerHandle_t xTimer )
{
Timer_t * const pxTimer = ( Timer_t * ) xTimer;
void *pvReturn;

	configASSERT( xTimer );

	taskENTER_CRITICAL();
	{
		pvReturn = pxTimer->pvTimerID;
	}
	taskEXIT_CRITICAL();

	return pvReturn;
}
/*-----------------------------------------------------------*/

  /*  更新软件定时器的pvTimerID */
void vTimerSetTimerID( const TimerHandle_t xTimer, void *pvNewID )
{
Timer_t * const pxTimer = ( Timer_t * ) xTimer;

	configASSERT( xTimer );

	taskENTER_CRITICAL();
	{
		pxTimer->pvTimerID = pvNewID;
	}
	taskEXIT_CRITICAL();
}
/*-----------------------------------------------------------*/

#if( INCLUDE_xTimerPendFunctionCall == 1 )

	BaseType_t xTimerPendFunctionCallFromISR( PendedFunction_t xFunctionToPend, void *pvParameter1, uint32_t ulParameter2, BaseType_t *pxHigherPriorityTaskWoken )
	{
	DaemonTaskMessage_t xMessage;
	BaseType_t xReturn;

		/* Complete the message with the function parameters and post it to the
		daemon task. */
		xMessage.xMessageID = tmrCOMMAND_EXECUTE_CALLBACK_FROM_ISR;
		xMessage.u.xCallbackParameters.pxCallbackFunction = xFunctionToPend;
		xMessage.u.xCallbackParameters.pvParameter1 = pvParameter1;
		xMessage.u.xCallbackParameters.ulParameter2 = ulParameter2;

		xReturn = xQueueSendFromISR( xTimerQueue, &xMessage, pxHigherPriorityTaskWoken );

		tracePEND_FUNC_CALL_FROM_ISR( xFunctionToPend, pvParameter1, ulParameter2, xReturn );

		return xReturn;
	}

#endif /* INCLUDE_xTimerPendFunctionCall */
/*-----------------------------------------------------------*/

#if( INCLUDE_xTimerPendFunctionCall == 1 )

	BaseType_t xTimerPendFunctionCall( PendedFunction_t xFunctionToPend, void *pvParameter1, uint32_t ulParameter2, TickType_t xTicksToWait )
	{
	DaemonTaskMessage_t xMessage;
	BaseType_t xReturn;

		/* This function can only be called after a timer has been created or
		after the scheduler has been started because, until then, the timer
		queue does not exist. */
		configASSERT( xTimerQueue );

		/* Complete the message with the function parameters and post it to the
		daemon task. */
		xMessage.xMessageID = tmrCOMMAND_EXECUTE_CALLBACK;
		xMessage.u.xCallbackParameters.pxCallbackFunction = xFunctionToPend;
		xMessage.u.xCallbackParameters.pvParameter1 = pvParameter1;
		xMessage.u.xCallbackParameters.ulParameter2 = ulParameter2;

		xReturn = xQueueSendToBack( xTimerQueue, &xMessage, xTicksToWait );

		tracePEND_FUNC_CALL( xFunctionToPend, pvParameter1, ulParameter2, xReturn );

		return xReturn;
	}

#endif /* INCLUDE_xTimerPendFunctionCall */
/*-----------------------------------------------------------*/

/* 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 */
 

 

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