tasks.c

一个开源的Modbus协议栈

		/* A delay time of zero just forces a reschedule. */
		if( xTicksToDelay > ( portTickType ) 0 )
		{
			vTaskSuspendAll();
			{
				/* A task that is removed from the event list while the
				scheduler is suspended will not get placed in the ready
				list or removed from the blocked list until the scheduler
				is resumed.
				
				This task cannot be in an event list as it is the currently
				executing task. */

				/* Calculate the time to wake - this may overflow but this is
				not a problem. */
				xTimeToWake = xTickCount + xTicksToDelay;

				/* We must remove ourselves from the ready list before adding
				ourselves to the blocked list as the same list item is used for
				both lists. */
				vListRemove( ( xListItem * ) &( pxCurrentTCB->xGenericListItem ) );

				/* The list item will be inserted in wake time order. */
				listSET_LIST_ITEM_VALUE( &( pxCurrentTCB->xGenericListItem ), xTimeToWake );

				if( xTimeToWake < xTickCount )
				{
					/* Wake time has overflowed.  Place this item in the
					overflow list. */
					vListInsert( ( xList * ) pxOverflowDelayedTaskList, ( xListItem * ) &( pxCurrentTCB->xGenericListItem ) );
				}
				else
				{
					/* The wake time has not overflowed, so we can use the
					current block list. */
					vListInsert( ( xList * ) pxDelayedTaskList, ( xListItem * ) &( pxCurrentTCB->xGenericListItem ) );
				}
			}
			xAlreadyYielded = xTaskResumeAll();
		}
		
		/* Force a reschedule if xTaskResumeAll has not already done so, we may
		have put ourselves to sleep. */
		if( !xAlreadyYielded )
		{
			taskYIELD();
		}
	}
	
#endif
/*-----------------------------------------------------------*/

#if ( INCLUDE_uxTaskPriorityGet == 1 )

	unsigned portBASE_TYPE uxTaskPriorityGet( xTaskHandle pxTask )
	{
	tskTCB *pxTCB;
	unsigned portBASE_TYPE uxReturn;

		taskENTER_CRITICAL();
		{
			/* If null is passed in here then we are changing the
			priority of the calling function. */
			pxTCB = prvGetTCBFromHandle( pxTask );
			uxReturn = pxTCB->uxPriority;
		}
		taskEXIT_CRITICAL();

		return uxReturn;
	}

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

#if ( INCLUDE_vTaskPrioritySet == 1 )

	void vTaskPrioritySet( xTaskHandle pxTask, unsigned portBASE_TYPE uxNewPriority )
	{
	tskTCB *pxTCB;
	unsigned portBASE_TYPE uxCurrentPriority, xYieldRequired = pdFALSE;

		/* Ensure the new priority is valid. */
		if( uxNewPriority >= configMAX_PRIORITIES )
		{
			uxNewPriority = configMAX_PRIORITIES - 1;
		}

		taskENTER_CRITICAL();
		{
			/* If null is passed in here then we are changing the
			priority of the calling function. */
			pxTCB = prvGetTCBFromHandle( pxTask );
			uxCurrentPriority = pxTCB->uxPriority;

			if( uxCurrentPriority != uxNewPriority )
			{
				/* The priority change may have readied a task of higher
				priority than the calling task. */
				if( uxNewPriority > pxCurrentTCB->uxPriority ) 
				{
					if( pxTask != NULL )
					{
						/* The priority of another task is being raised.  If we
						were raising the priority of the currently running task
						there would be no need to switch as it must have already
						been the highest priority task. */
						xYieldRequired = pdTRUE;
					}
				}
				else if( pxTask == NULL )
				{
					/* Setting our own priority down means there may now be another
					task of higher priority that is ready to execute. */
					xYieldRequired = pdTRUE;
				}
			
				pxTCB->uxPriority = uxNewPriority;
				listSET_LIST_ITEM_VALUE( &( pxTCB->xEventListItem ), configMAX_PRIORITIES - ( portTickType ) uxNewPriority );

				/* If the task is in the blocked or suspended list we need do
				nothing more than change it's priority variable. However, if
				the task is in a ready list it needs to be removed and placed
				in the queue appropriate to its new priority. */
				if( listIS_CONTAINED_WITHIN( &( pxReadyTasksLists[ uxCurrentPriority ] ), &( pxTCB->xGenericListItem ) ) )
				{
					/* The task is currently in its ready list - remove before adding
					it to it's new ready list.  As we are in a critical section we
					can do this even if the scheduler is suspended. */
					vListRemove( &( pxTCB->xGenericListItem ) );
					prvAddTaskToReadyQueue( pxTCB );
				}			
				
				if( xYieldRequired == pdTRUE )
				{
					taskYIELD();
				}				
			}
		}
		taskEXIT_CRITICAL();
	}

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

#if ( INCLUDE_vTaskSuspend == 1 )

	void vTaskSuspend( xTaskHandle pxTaskToSuspend )
	{
	tskTCB *pxTCB;

		taskENTER_CRITICAL();
		{
			/* Ensure a yield is performed if the current task is being 
			suspended. */
			if( pxTaskToSuspend == pxCurrentTCB )
			{
				pxTaskToSuspend = NULL;
			}

			/* If null is passed in here then we are suspending ourselves. */
			pxTCB = prvGetTCBFromHandle( pxTaskToSuspend );

			/* Remove task from the ready/delayed list and place in the	suspended list. */
			vListRemove( &( pxTCB->xGenericListItem ) );

			/* Is the task waiting on an event also? */												
			if( pxTCB->xEventListItem.pvContainer )
			{
				vListRemove( &( pxTCB->xEventListItem ) );
			}

			vListInsertEnd( ( xList * ) &xSuspendedTaskList, &( pxTCB->xGenericListItem ) );
		}
		taskEXIT_CRITICAL();

		/* We may have just suspended the current task. */
		if( ( void * ) pxTaskToSuspend == NULL )
		{
			taskYIELD();
		}
	}

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

#if ( INCLUDE_vTaskSuspend == 1 )

	static portBASE_TYPE prvIsTaskSuspended( const tskTCB * const pxTCB )
	{
	portBASE_TYPE xReturn = pdFALSE;

		/* Is the task we are attempting to resume actually in the
		suspended list? */
		if( listIS_CONTAINED_WITHIN( &xSuspendedTaskList, &( pxTCB->xGenericListItem ) ) != pdFALSE )
		{
			/* Has the task already been resumed from within an ISR? */
			if( listIS_CONTAINED_WITHIN( &xPendingReadyList, &( pxTCB->xEventListItem ) ) != pdTRUE )
			{			
				/* Is it in the suspended list because it is in the
				Suspended state?  It is possible to be in the suspended
				list because it is blocked on a task with no timeout
				specified. */
				if( listIS_CONTAINED_WITHIN( NULL, &( pxTCB->xEventListItem ) ) == pdTRUE )
				{
					xReturn = pdTRUE;
				}
			}
		}

		return xReturn;
	}

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

#if ( INCLUDE_vTaskSuspend == 1 )

	void vTaskResume( xTaskHandle pxTaskToResume )
	{
	tskTCB *pxTCB;

		/* Remove the task from whichever list it is currently in, and place
		it in the ready list. */
		pxTCB = ( tskTCB * ) pxTaskToResume;

		/* The parameter cannot be NULL as it is impossible to resume the
		currently executing task. */
		if( pxTCB != NULL )
		{
			taskENTER_CRITICAL();
			{
				if( prvIsTaskSuspended( pxTCB ) == pdTRUE )
				{
					/* As we are in a critical section we can access the ready
					lists even if the scheduler is suspended. */
					vListRemove(  &( pxTCB->xGenericListItem ) );
					prvAddTaskToReadyQueue( pxTCB );

					/* We may have just resumed a higher priority task. */
					if( pxTCB->uxPriority >= pxCurrentTCB->uxPriority )
					{
						/* This yield may not cause the task just resumed to run, but
						will leave the lists in the correct state for the next yield. */
						taskYIELD();
					}
				}
			}
			taskEXIT_CRITICAL();
		}
	}

#endif

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

#if ( ( INCLUDE_xTaskResumeFromISR == 1 ) && ( INCLUDE_vTaskSuspend == 1 ) )

	portBASE_TYPE xTaskResumeFromISR( xTaskHandle pxTaskToResume )
	{
	portBASE_TYPE xYieldRequired = pdFALSE;
	tskTCB *pxTCB;

		pxTCB = ( tskTCB * ) pxTaskToResume;

		if( prvIsTaskSuspended( pxTCB ) == pdTRUE )
		{
			if( uxSchedulerSuspended == ( unsigned portBASE_TYPE ) pdFALSE )
			{
				xYieldRequired = ( pxTCB->uxPriority >= pxCurrentTCB->uxPriority );
				vListRemove(  &( pxTCB->xGenericListItem ) );	
				prvAddTaskToReadyQueue( pxTCB );
			}
			else
			{
				/* We cannot access the delayed or ready lists, so will hold this
				task pending until the scheduler is resumed, at which point a
				yield will be preformed if necessary. */
				vListInsertEnd( ( xList * ) &( xPendingReadyList ), &( pxTCB->xEventListItem ) );
			}
		}

		return xYieldRequired;
	}

#endif




/*-----------------------------------------------------------
 * PUBLIC SCHEDULER CONTROL documented in task.h
 *----------------------------------------------------------*/


void vTaskStartScheduler( void )
{
portBASE_TYPE xReturn;

	/* Add the idle task at the lowest priority. */
	xReturn = xTaskCreate( prvIdleTask, ( signed portCHAR * ) "IDLE", tskIDLE_STACK_SIZE, ( void * ) NULL, tskIDLE_PRIORITY, ( xTaskHandle * ) NULL );

	if( xReturn == pdPASS )
	{
		/* Interrupts are turned off here, to ensure a tick does not occur
		before or during the call to xPortStartScheduler().  The stacks of
		the created tasks contain a status word with interrupts switched on
		so interrupts will automatically get re-enabled when the first task
		starts to run.
		
		STEPPING THROUGH HERE USING A DEBUGGER CAN CAUSE BIG PROBLEMS IF THE
		DEBUGGER ALLOWS INTERRUPTS TO BE PROCESSED. */
		portDISABLE_INTERRUPTS();

		xSchedulerRunning = pdTRUE;
		xTickCount = ( portTickType ) 0;

		/* Setting up the timer tick is hardware specific and thus in the
		portable interface. */
		if( xPortStartScheduler() )
		{
			/* Should not reach here as if the scheduler is running the
			function will not return. */
		}
		else
		{
			/* Should only reach here if a task calls xTaskEndScheduler(). */
		}
	}
}
/*-----------------------------------------------------------*/

void vTaskEndScheduler( void )
{
	/* Stop the scheduler interrupts and call the portable scheduler end
	routine so the original ISRs can be restored if necessary.  The port
	layer must ensure interrupts enable	bit is left in the correct state. */
	portDISABLE_INTERRUPTS();
	xSchedulerRunning = pdFALSE;
	vPortEndScheduler();
}
/*----------------------------------------------------------*/

void vTaskSuspendAll( void )
{
	portENTER_CRITICAL();
		++uxSchedulerSuspended;
	portEXIT_CRITICAL();
}
/*----------------------------------------------------------*/

signed portBASE_TYPE xTaskResumeAll( void )
{
register tskTCB *pxTCB;
signed portBASE_TYPE xAlreadyYielded = pdFALSE;

	/* It is possible that an ISR caused a task to be removed from an event
	list while the scheduler was suspended.  If this was the case then the
	removed task will have been added to the xPendingReadyList.  Once the
	scheduler has been resumed it is safe to move all the pending ready
	tasks from this list into their appropriate ready list. */
	portENTER_CRITICAL();
	{
		--uxSchedulerSuspended;

		if( uxSchedulerSuspended == ( unsigned portBASE_TYPE ) pdFALSE )
		{			
			if( uxCurrentNumberOfTasks > ( unsigned portBASE_TYPE ) 0 )
			{
				portBASE_TYPE xYieldRequired = pdFALSE;
				
				/* Move any readied tasks from the pending list into the
				appropriate ready list. */
				while( ( pxTCB = ( tskTCB * ) listGET_OWNER_OF_HEAD_ENTRY(  ( ( xList * ) &xPendingReadyList ) ) ) != NULL )
				{
					vListRemove( &( pxTCB->xEventListItem ) );
					vListRemove( &( pxTCB->xGenericListItem ) );
					prvAddTaskToReadyQueue( pxTCB );
					
					/* If we have moved a task that has a priority higher than
					the current task then we should yield. */
					if( pxTCB->uxPriority >= pxCurrentTCB->uxPriority )
					{
						xYieldRequired = pdTRUE;
					}
				}

				/* If any ticks occurred while the scheduler was suspended then