queue.c

FreeRTOS source code as bundled with the book "Using FreeRTOS Real-Time Kernel - A Practical Approac

					}
					else
					{
						traceQUEUE_PEEK( pxQueue );

						/* We are not removing the data, so reset our read
						pointer. */
						pxQueue->pcReadFrom = pcOriginalReadPosition;

						/* The data is being left in the queue, so see if there are
						any other tasks waiting for the data. */
						if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) )
						{
							/* Tasks that are removed from the event list will get added to
							the pending ready list as the scheduler is still suspended. */
							if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
							{
								/* The task waiting has a higher priority that this task. */
								taskYIELD();
							}
						}

					}

					xReturn = pdPASS;
				}
				else
				{
					xReturn = errQUEUE_EMPTY;
				}
			}
			taskEXIT_CRITICAL();

			if( xReturn == errQUEUE_EMPTY )
			{
				if( xTicksToWait > ( portTickType ) 0 )
				{
					if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
					{
						xReturn = queueERRONEOUS_UNBLOCK;
					}
					else
					{
						traceQUEUE_RECEIVE_FAILED( pxQueue );
					}
				}
				else
				{
					traceQUEUE_RECEIVE_FAILED( pxQueue );
				}
			}
		} while( xReturn == queueERRONEOUS_UNBLOCK );

		return xReturn;
	}


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

signed portBASE_TYPE xQueueGenericSendFromISR( xQueueHandle pxQueue, const void * const pvItemToQueue, signed portBASE_TYPE *pxHigherPriorityTaskWoken, portBASE_TYPE xCopyPosition )
{
signed portBASE_TYPE xReturn;
unsigned portBASE_TYPE uxSavedInterruptStatus;

	/* Similar to xQueueGenericSend, except we don't block if there is no room
	in the queue.  Also we don't directly wake a task that was blocked on a
	queue read, instead we return a flag to say whether a context switch is
	required or not (i.e. has a task with a higher priority than us been woken
	by this	post). */
	uxSavedInterruptStatus = portSET_INTERRUPT_MASK_FROM_ISR();
	{
		if( pxQueue->uxMessagesWaiting < pxQueue->uxLength )
		{
			traceQUEUE_SEND_FROM_ISR( pxQueue );

			prvCopyDataToQueue( pxQueue, pvItemToQueue, xCopyPosition );

			/* If the queue is locked we do not alter the event list.  This will
			be done when the queue is unlocked later. */
			if( pxQueue->xTxLock == queueUNLOCKED )
			{
				if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) )
				{
					if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
					{
						/* The task waiting has a higher priority so record that a
						context	switch is required. */
						*pxHigherPriorityTaskWoken = pdTRUE;
					}
				}
			}
			else
			{
				/* Increment the lock count so the task that unlocks the queue
				knows that data was posted while it was locked. */
				++( pxQueue->xTxLock );
			}

			xReturn = pdPASS;
		}
		else
		{
			traceQUEUE_SEND_FROM_ISR_FAILED( pxQueue );
			xReturn = errQUEUE_FULL;
		}
	}
	portCLEAR_INTERRUPT_MASK_FROM_ISR( uxSavedInterruptStatus );

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

signed portBASE_TYPE xQueueGenericReceive( xQueueHandle pxQueue, void * const pvBuffer, portTickType xTicksToWait, portBASE_TYPE xJustPeeking )
{
signed portBASE_TYPE xReturn = pdTRUE;
xTimeOutType xTimeOut;
signed portCHAR *pcOriginalReadPosition;

	do
	{
		/* If there are no messages in the queue we may have to block. */
		if( xTicksToWait > ( portTickType ) 0 )
		{
			vTaskSuspendAll();
			prvLockQueue( pxQueue );

			if( xReturn == pdTRUE )
			{
				/* This is the first time through - we need to capture the
				time while the scheduler is locked to ensure we attempt to
				block at least once. */
				vTaskSetTimeOutState( &xTimeOut );
			}

			if( prvIsQueueEmpty( pxQueue ) )
			{
	    		/* Need to call xTaskCheckForTimeout again as time could
	    		have passed since it was last called if this is not the
	    		first time around this loop. */
				if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
				{
					traceBLOCKING_ON_QUEUE_RECEIVE( pxQueue );

					#if ( configUSE_MUTEXES == 1 )
					{
						if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
						{
							portENTER_CRITICAL();
								vTaskPriorityInherit( ( void * ) pxQueue->pxMutexHolder );
							portEXIT_CRITICAL();
						}
					}
					#endif

					vTaskPlaceOnEventList( &( pxQueue->xTasksWaitingToReceive ), xTicksToWait );
					prvUnlockQueue( pxQueue );
					if( !xTaskResumeAll() )
					{
						taskYIELD();
					}
				}
				else
				{
					prvUnlockQueue( pxQueue );
					( void ) xTaskResumeAll();
				}
			}
			else
			{
				prvUnlockQueue( pxQueue );
				( void ) xTaskResumeAll();
			}
		}

/* The two tasks are blocked on the queue, the low priority task is polling/running. */

/* An interrupt occurs here - which unblocks the HP tasks, but they do not run. */
		taskENTER_CRITICAL();
		{
/* Because the interrupt occurred the LP task manages to grab the data as the other two tasks are not yet running. */
			if( pxQueue->uxMessagesWaiting > ( unsigned portBASE_TYPE ) 0 )
			{
				/* Remember our read position in case we are just peeking. */
				pcOriginalReadPosition = pxQueue->pcReadFrom;

				prvCopyDataFromQueue( pxQueue, pvBuffer );

				if( xJustPeeking == pdFALSE )
				{
					traceQUEUE_RECEIVE( pxQueue );

					/* We are actually removing data. */
					--( pxQueue->uxMessagesWaiting );

					#if ( configUSE_MUTEXES == 1 )
					{
						if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
						{
							/* Record the information required to implement
							priority inheritance should it become necessary. */
							pxQueue->pxMutexHolder = xTaskGetCurrentTaskHandle();
						}
					}
					#endif

					if( listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) == pdFALSE )
					{
						if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) == pdTRUE )
						{
							taskYIELD();
						}
					}
				}
				else
				{
					traceQUEUE_PEEK( pxQueue );

					/* We are not removing the data, so reset our read
					pointer. */
					pxQueue->pcReadFrom = pcOriginalReadPosition;

					/* The data is being left in the queue, so see if there are
					any other tasks waiting for the data. */
					if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToReceive ) ) )
					{
						/* Tasks that are removed from the event list will get added to
						the pending ready list as the scheduler is still suspended. */
						if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToReceive ) ) != pdFALSE )
						{
							/* The task waiting has a higher priority than this task. */
							taskYIELD();
						}
					}

				}

				xReturn = pdPASS;
			}
			else
			{
				xReturn = errQUEUE_EMPTY;
			}
		}
		taskEXIT_CRITICAL();

		if( xReturn == errQUEUE_EMPTY )
		{
			if( xTicksToWait > ( portTickType ) 0 )
			{
				if( xTaskCheckForTimeOut( &xTimeOut, &xTicksToWait ) == pdFALSE )
				{
					xReturn = queueERRONEOUS_UNBLOCK;
				}
				else
				{
					traceQUEUE_RECEIVE_FAILED( pxQueue );
				}
			}
			else
			{
				traceQUEUE_RECEIVE_FAILED( pxQueue );
			}
		}

	} while( xReturn == queueERRONEOUS_UNBLOCK );

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

signed portBASE_TYPE xQueueReceiveFromISR( xQueueHandle pxQueue, void * const pvBuffer, signed portBASE_TYPE *pxTaskWoken )
{
signed portBASE_TYPE xReturn;
unsigned portBASE_TYPE uxSavedInterruptStatus;

	uxSavedInterruptStatus = portSET_INTERRUPT_MASK_FROM_ISR();
	{
		/* We cannot block from an ISR, so check there is data available. */
		if( pxQueue->uxMessagesWaiting > ( unsigned portBASE_TYPE ) 0 )
		{
			traceQUEUE_RECEIVE_FROM_ISR( pxQueue );

			prvCopyDataFromQueue( pxQueue, pvBuffer );
			--( pxQueue->uxMessagesWaiting );

			/* If the queue is locked we will not modify the event list.  Instead
			we update the lock count so the task that unlocks the queue will know
			that an ISR has removed data while the queue was locked. */
			if( pxQueue->xRxLock == queueUNLOCKED )
			{
				if( !listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) )
				{
					if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) != pdFALSE )
					{
						/* The task waiting has a higher priority than us so
						force a context switch. */
						*pxTaskWoken = pdTRUE;
					}
				}
			}
			else
			{
				/* Increment the lock count so the task that unlocks the queue
				knows that data was removed while it was locked. */
				++( pxQueue->xRxLock );
			}

			xReturn = pdPASS;
		}
		else
		{
			xReturn = pdFAIL;
			traceQUEUE_RECEIVE_FROM_ISR_FAILED( pxQueue );
		}
	}
	portCLEAR_INTERRUPT_MASK_FROM_ISR( uxSavedInterruptStatus );

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

unsigned portBASE_TYPE uxQueueMessagesWaiting( const xQueueHandle pxQueue )
{
unsigned portBASE_TYPE uxReturn;

	taskENTER_CRITICAL();
		uxReturn = pxQueue->uxMessagesWaiting;
	taskEXIT_CRITICAL();

	return uxReturn;
}
/*-----------------------------------------------------------*/

unsigned portBASE_TYPE uxQueueMessagesWaitingFromISR( const xQueueHandle pxQueue )
{
unsigned portBASE_TYPE uxReturn;

	uxReturn = pxQueue->uxMessagesWaiting;

	return uxReturn;
}
/*-----------------------------------------------------------*/

void vQueueDelete( xQueueHandle pxQueue )
{
	traceQUEUE_DELETE( pxQueue );
	vQueueUnregisterQueue( pxQueue );
	vPortFree( pxQueue->pcHead );
	vPortFree( pxQueue );
}
/*-----------------------------------------------------------*/

static void prvCopyDataToQueue( xQUEUE *pxQueue, const void *pvItemToQueue, portBASE_TYPE xPosition )
{
	if( pxQueue->uxItemSize == ( unsigned portBASE_TYPE ) 0 )
	{
		#if ( configUSE_MUTEXES == 1 )
		{
			if( pxQueue->uxQueueType == queueQUEUE_IS_MUTEX )
			{
				/* The mutex is no longer being held. */
				vTaskPriorityDisinherit( ( void * ) pxQueue->pxMutexHolder );
                pxQueue->pxMutexHolder = NULL;
			}
		}
		#endif
	}
	else if( xPosition == queueSEND_TO_BACK )
	{
		memcpy( ( void * ) pxQueue->pcWriteTo, pvItemToQueue, ( unsigned ) pxQueue->uxItemSize );
		pxQueue->pcWriteTo += pxQueue->uxItemSize;
		if( pxQueue->pcWriteTo >= pxQueue->pcTail )
		{
			pxQueue->pcWriteTo = pxQueue->pcHead;
		}
	}
	else
	{
		memcpy( ( void * ) pxQueue->pcReadFrom, pvItemToQueue, ( unsigned ) pxQueue->uxItemSize );
		pxQueue->pcReadFrom -= pxQueue->uxItemSize;
		if( pxQueue->pcReadFrom < pxQueue->pcHead )
		{
			pxQueue->pcReadFrom = ( pxQueue->pcTail - pxQueue->uxItemSize );
		}