Queue Receiving from ISR

Group that contains macros & functions for receiving queue data from an Interrupt Service Routine. More...

Collaboration diagram for Queue Receiving from ISR:

Functions
BaseType_t	xQueuePeekFromISR (QueueHandle_t xQueue, void *const pvBuffer) PRIVILEGED_FUNCTION

Detailed Description

Group that contains macros & functions for receiving queue data from an Interrupt Service Routine.

queue. h

BaseType_t xQueueReceiveFromISR(
                                      QueueHandle_t    xQueue,
                                      void *pvBuffer,
                                      BaseType_t *pxTaskWoken
                                  );
  

Receive an item from a queue. It is safe to use this function from within an interrupt service routine.

Parameters

xQueue	The handle to the queue from which the item is to be received.
pvBuffer	Pointer to the buffer into which the received item will be copied.
pxTaskWoken	A task may be blocked waiting for space to become available on the queue. If xQueueReceiveFromISR causes such a task to unblock *pxTaskWoken will get set to pdTRUE, otherwise *pxTaskWoken will remain unchanged.

Returns

pdTRUE if an item was successfully received from the queue, otherwise pdFALSE.

Example usage:

QueueHandle_t xQueue;

// Function to create a queue and post some values.
void vAFunction( void *pvParameters )
{
char cValueToPost;
const TickType_t xTicksToWait = ( TickType_t )0xff;

   // Create a queue capable of containing 10 characters.
   xQueue = xQueueCreate( 10, sizeof( char ) );
   if( xQueue == 0 )
   {
       // Failed to create the queue.
   }

   // ...

   // Post some characters that will be used within an ISR.  If the queue
   // is full then this task will block for xTicksToWait ticks.
   cValueToPost = 'a';
   xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );
   cValueToPost = 'b';
   xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );

   // ... keep posting characters ... this task may block when the queue
   // becomes full.

   cValueToPost = 'c';
   xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );
}

// ISR that outputs all the characters received on the queue.
void vISR_Routine( void )
{
BaseType_t xTaskWokenByReceive = pdFALSE;
char cRxedChar;

   while( xQueueReceiveFromISR( xQueue, ( void * ) &cRxedChar, &xTaskWokenByReceive) )
   {
       // A character was received.  Output the character now.
       vOutputCharacter( cRxedChar );

       // If removing the character from the queue woke the task that was
       // posting onto the queue cTaskWokenByReceive will have been set to
       // pdTRUE.  No matter how many times this loop iterates only one
       // task will be woken.
   }

   if( cTaskWokenByPost != ( char ) pdFALSE;
   {
       taskYIELD ();
   }
}

Function Documentation

xQueuePeekFromISR()

BaseType_t xQueuePeekFromISR	(	QueueHandle_t	xQueue,
		void *const	pvBuffer
	)

#include <queue.h>

BaseType_t xQueuePeekFromISR(
                                   QueueHandle_t xQueue,
                                   void *pvBuffer,
                               );

A version of xQueuePeek() that can be called from an interrupt service routine (ISR).

Receive an item from a queue without removing the item from the queue. The item is received by copy so a buffer of adequate size must be provided. The number of bytes copied into the buffer was defined when the queue was created.

Successfully received items remain on the queue so will be returned again by the next call, or a call to xQueueReceive().

Parameters

xQueue	The handle to the queue from which the item is to be received.
pvBuffer	Pointer to the buffer into which the received item will be copied.

Returns

pdTRUE if an item was successfully received from the queue, otherwise pdFALSE.