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xQueueReceiveFromISR
[Queue Management]

queue. h

 portBASE_TYPE xQueueReceiveFromISR( 
                                       xQueueHandle pxQueue, 
                                       void *pvBuffer, 
                                       portBASE_TYPE *pxTaskWoken 
                                   ); 
 

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

Parameters:

pxQueue	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:

 xQueueHandle xQueue;

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

    // Create a queue capable of containing 10 characters.
    xQueue = xQueueCreate( 10, sizeof( portCHAR ) );
    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 xBlockTime ticks.
    cValueToPost = 'a';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xBlockTime );
    cValueToPost = 'b';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xBlockTime );

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

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

 // ISR that outputs all the characters received on the queue. 
 void vISR_Routine( void )
 {
 portBASE_TYPE xTaskWokenByReceive = pdFALSE;
 portCHAR 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 xTaskWokenByReceive will have been set to
        // pdTRUE.  No matter how many times this loop iterates only one
        // task will be woken.
    }

    if( xTaskWokenByPost != pdFALSE )
    {
        // We should switch context so the ISR returns to a different task.
        // NOTE:  How this is done depends on the port you are using.  Check
        // the documentation and examples for your port.
        taskYIELD ();
    }
 }
 

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