Queues

xQueueCreate

queue. h

 xQueueHandle xQueueCreate(
         unsigned portBASE_TYPE uxQueueLength,
         unsigned portBASE_TYPE uxItemSize
        );

Creates a new queue instance. This allocates the storage required by the new queue and returns a handle for the queue.

Parameters:

uxQueueLength	The maximum number of items that the queue can contain.
uxItemSize	The number of bytes each item in the queue will require. Items are queued by copy, not by reference, so this is the number of bytes that will be copied for each posted item. Each item on the queue must be the same size.

Returns:

If the queue is successfully create then a handle to the newly created queue is returned. If the queue cannot be created then 0 is returned.

Example usage:

 struct AMessage
 {
 char ucMessageID;
 char ucData[ 20 ];
 };

 void vATask( void *pvParameters )
 {
 xQueueHandle xQueue1, xQueue2;

 // Create a queue capable of containing 10 unsigned long values.
 xQueue1 = xQueueCreate( 10, sizeof( unsigned long ) );
 if( xQueue1 == 0 )
 {
  // Queue was not created and must not be used.
 }

 // Create a queue capable of containing 10 pointers to AMessage structures.
 // These should be passed by pointer as they contain a lot of data.
 xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );
 if( xQueue2 == 0 )
 {
  // Queue was not created and must not be used.
 }

 // ... Rest of task code.
 }

xQueueSendToFront

queue. h

 portBASE_TYPE xQueueSendToFront(
           xQueueHandle xQueue,
           const void * pvItemToQueue,
           portTickType xTicksToWait
          );

This is a macro that calls xQueueGenericSend().

Post an item to the front of a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR.

Parameters:

xQueue	The handle to the queue on which the item is to be posted.
pvItemToQueue	A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area.
xTicksToWait	The maximum amount of time the task should block waiting for space to become available on the queue, should it already be full. The call will return immediately if this is set to 0 and the queue is full. The time is defined in tick periods so the constant portTICK_RATE_MS should be used to convert to real time if this is required.

Returns:

pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL.

Example usage:

 struct AMessage
 {
 char ucMessageID;
 char ucData[ 20 ];
 } xMessage;

 unsigned long ulVar = 10UL;

 void vATask( void *pvParameters )
 {
 xQueueHandle xQueue1, xQueue2;
 struct AMessage *pxMessage;

 // Create a queue capable of containing 10 unsigned long values.
 xQueue1 = xQueueCreate( 10, sizeof( unsigned long ) );

 // Create a queue capable of containing 10 pointers to AMessage structures.
 // These should be passed by pointer as they contain a lot of data.
 xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );

 // ...

 if( xQueue1 != 0 )
 {
  // Send an unsigned long.  Wait for 10 ticks for space to become
  // available if necessary.
  if( xQueueSendToFront( xQueue1, ( void * ) &ulVar, ( portTickType ) 10 ) != pdPASS )
  {
   // Failed to post the message, even after 10 ticks.
  }
 }

 if( xQueue2 != 0 )
 {
  // Send a pointer to a struct AMessage object.  Don't block if the
  // queue is already full.
  pxMessage = & xMessage;
  xQueueSendToFront( xQueue2, ( void * ) &pxMessage, ( portTickType ) 0 );
 }

 // ... Rest of task code.
 }

xQueueSendToBack

queue. h

 portBASE_TYPE xQueueSendToBack(
           xQueueHandle xQueue,
           const void * pvItemToQueue,
           portTickType xTicksToWait
          );

This is a macro that calls xQueueGenericSend().

Post an item to the back of a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR.

Parameters:

xQueue	The handle to the queue on which the item is to be posted.
pvItemToQueue	A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area.
xTicksToWait	The maximum amount of time the task should block waiting for space to become available on the queue, should it already be full. The call will return immediately if this is set to 0 and the queue is full. The time is defined in tick periods so the constant portTICK_RATE_MS should be used to convert to real time if this is required.

Returns:

pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL.

Example usage:

 struct AMessage
 {
 char ucMessageID;
 char ucData[ 20 ];
 } xMessage;

 unsigned long ulVar = 10UL;

 void vATask( void *pvParameters )
 {
 xQueueHandle xQueue1, xQueue2;
 struct AMessage *pxMessage;

 // Create a queue capable of containing 10 unsigned long values.
 xQueue1 = xQueueCreate( 10, sizeof( unsigned long ) );

 // Create a queue capable of containing 10 pointers to AMessage structures.
 // These should be passed by pointer as they contain a lot of data.
 xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );

 // ...

 if( xQueue1 != 0 )
 {
  // Send an unsigned long.  Wait for 10 ticks for space to become
  // available if necessary.
  if( xQueueSendToBack( xQueue1, ( void * ) &ulVar, ( portTickType ) 10 ) != pdPASS )
  {
   // Failed to post the message, even after 10 ticks.
  }
 }

 if( xQueue2 != 0 )
 {
  // Send a pointer to a struct AMessage object.  Don't block if the
  // queue is already full.
  pxMessage = & xMessage;
  xQueueSendToBack( xQueue2, ( void * ) &pxMessage, ( portTickType ) 0 );
 }

 // ... Rest of task code.
 }

xQueueSend

queue. h

 portBASE_TYPE xQueueSend(
         xQueueHandle xQueue,
         const void * pvItemToQueue,
         portTickType xTicksToWait
       );

This is a macro that calls xQueueGenericSend(). It is included for backward compatibility with versions of FreeRTOS.org that did not include the xQueueSendToFront() and xQueueSendToBack() macros. It is equivalent to xQueueSendToBack().

Post an item on a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR.

Parameters:

xQueue	The handle to the queue on which the item is to be posted.
pvItemToQueue	A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area.
xTicksToWait	The maximum amount of time the task should block waiting for space to become available on the queue, should it already be full. The call will return immediately if this is set to 0 and the queue is full. The time is defined in tick periods so the constant portTICK_RATE_MS should be used to convert to real time if this is required.

Returns:

pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL.

Example usage:

 struct AMessage
 {
 char ucMessageID;
 char ucData[ 20 ];
 } xMessage;

 unsigned long ulVar = 10UL;

 void vATask( void *pvParameters )
 {
 xQueueHandle xQueue1, xQueue2;
 struct AMessage *pxMessage;

 // Create a queue capable of containing 10 unsigned long values.
 xQueue1 = xQueueCreate( 10, sizeof( unsigned long ) );

 // Create a queue capable of containing 10 pointers to AMessage structures.
 // These should be passed by pointer as they contain a lot of data.
 xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );

 // ...

 if( xQueue1 != 0 )
 {
  // Send an unsigned long.  Wait for 10 ticks for space to become
  // available if necessary.
  if( xQueueSend( xQueue1, ( void * ) &ulVar, ( portTickType ) 10 ) != pdPASS )
  {
   // Failed to post the message, even after 10 ticks.
  }
 }

 if( xQueue2 != 0 )
 {
  // Send a pointer to a struct AMessage object.  Don't block if the
  // queue is already full.
  pxMessage = & xMessage;
  xQueueSend( xQueue2, ( void * ) &pxMessage, ( portTickType ) 0 );
 }

 // ... Rest of task code.
 }

xQueueGenericSend

queue. h

 portBASE_TYPE xQueueGenericSend(
         xQueueHandle xQueue,
         const void * pvItemToQueue,
         portTickType xTicksToWait
         portBASE_TYPE xCopyPosition
        );

It is preferred that the macros xQueueSend(), xQueueSendToFront() and xQueueSendToBack() are used in place of calling this function directly.

Post an item on a queue. The item is queued by copy, not by reference. This function must not be called from an interrupt service routine. See xQueueSendFromISR () for an alternative which may be used in an ISR.

Parameters:

xQueue	The handle to the queue on which the item is to be posted.
pvItemToQueue	A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area.
xTicksToWait	The maximum amount of time the task should block waiting for space to become available on the queue, should it already be full. The call will return immediately if this is set to 0 and the queue is full. The time is defined in tick periods so the constant portTICK_RATE_MS should be used to convert to real time if this is required.
xCopyPosition	Can take the value queueSEND_TO_BACK to place the item at the back of the queue, or queueSEND_TO_FRONT to place the item at the front of the queue (for high priority messages).

Returns:

pdTRUE if the item was successfully posted, otherwise errQUEUE_FULL.

Example usage:

 struct AMessage
 {
 char ucMessageID;
 char ucData[ 20 ];
 } xMessage;

 unsigned long ulVar = 10UL;

 void vATask( void *pvParameters )
 {
 xQueueHandle xQueue1, xQueue2;
 struct AMessage *pxMessage;

 // Create a queue capable of containing 10 unsigned long values.
 xQueue1 = xQueueCreate( 10, sizeof( unsigned long ) );

 // Create a queue capable of containing 10 pointers to AMessage structures.
 // These should be passed by pointer as they contain a lot of data.
 xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );

 // ...

 if( xQueue1 != 0 )
 {
  // Send an unsigned long.  Wait for 10 ticks for space to become
  // available if necessary.
  if( xQueueGenericSend( xQueue1, ( void * ) &ulVar, ( portTickType ) 10, queueSEND_TO_BACK ) != pdPASS )
  {
   // Failed to post the message, even after 10 ticks.
  }
 }

 if( xQueue2 != 0 )
 {
  // Send a pointer to a struct AMessage object.  Don't block if the
  // queue is already full.
  pxMessage = & xMessage;
  xQueueGenericSend( xQueue2, ( void * ) &pxMessage, ( portTickType ) 0, queueSEND_TO_BACK );
 }

 // ... Rest of task code.
 }

xQueuePeek

queue. h

 portBASE_TYPE xQueuePeek(
        xQueueHandle xQueue,
        void *pvBuffer,
        portTickType xTicksToWait
       ); 

This is a macro that calls the xQueueGenericReceive() function.

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().

This macro must not be used in 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.
xTicksToWait	The maximum amount of time the task should block waiting for an item to receive should the queue be empty at the time of the call. The time is defined in tick periods so the constant portTICK_RATE_MS should be used to convert to real time if this is required. xQueuePeek() will return immediately if xTicksToWait is 0 and the queue is empty.

Returns:

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

Example usage:

 struct AMessage
 {
 char ucMessageID;
 char ucData[ 20 ];
 } xMessage;

 xQueueHandle xQueue;

 // Task to create a queue and post a value.
 void vATask( void *pvParameters )
 {
 struct AMessage *pxMessage;

 // Create a queue capable of containing 10 pointers to AMessage structures.
 // These should be passed by pointer as they contain a lot of data.
 xQueue = xQueueCreate( 10, sizeof( struct AMessage * ) );
 if( xQueue == 0 )
 {
  // Failed to create the queue.
 }

 // ...

 // Send a pointer to a struct AMessage object.  Don't block if the
 // queue is already full.
 pxMessage = & xMessage;
 xQueueSend( xQueue, ( void * ) &pxMessage, ( portTickType ) 0 );

 // ... Rest of task code.
 }

 // Task to peek the data from the queue.
 void vADifferentTask( void *pvParameters )
 {
 struct AMessage *pxRxedMessage;

 if( xQueue != 0 )
 {
  // Peek a message on the created queue.  Block for 10 ticks if a
  // message is not immediately available.
  if( xQueuePeek( xQueue, &( pxRxedMessage ), ( portTickType ) 10 ) )
  {
   // pcRxedMessage now points to the struct AMessage variable posted
   // by vATask, but the item still remains on the queue.
  }
 }

 // ... Rest of task code.
 }

xQueueReceive

queue. h

 portBASE_TYPE xQueueReceive(
         xQueueHandle xQueue,
         void *pvBuffer,
         portTickType xTicksToWait
       ); 

This is a macro that calls the xQueueGenericReceive() function.

Receive an item from a 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 are removed from the queue.

This function must not be used in an interrupt service routine. See xQueueReceiveFromISR for an alternative that can.

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.
xTicksToWait	The maximum amount of time the task should block waiting for an item to receive should the queue be empty at the time of the call. xQueueReceive() will return immediately if xTicksToWait is zero and the queue is empty. The time is defined in tick periods so the constant portTICK_RATE_MS should be used to convert to real time if this is required.

Returns:

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

Example usage:

 struct AMessage
 {
 char ucMessageID;
 char ucData[ 20 ];
 } xMessage;

 xQueueHandle xQueue;

 // Task to create a queue and post a value.
 void vATask( void *pvParameters )
 {
 struct AMessage *pxMessage;

 // Create a queue capable of containing 10 pointers to AMessage structures.
 // These should be passed by pointer as they contain a lot of data.
 xQueue = xQueueCreate( 10, sizeof( struct AMessage * ) );
 if( xQueue == 0 )
 {
  // Failed to create the queue.
 }

 // ...

 // Send a pointer to a struct AMessage object.  Don't block if the
 // queue is already full.
 pxMessage = & xMessage;
 xQueueSend( xQueue, ( void * ) &pxMessage, ( portTickType ) 0 );

 // ... Rest of task code.
 }

 // Task to receive from the queue.
 void vADifferentTask( void *pvParameters )
 {
 struct AMessage *pxRxedMessage;

 if( xQueue != 0 )
 {
  // Receive a message on the created queue.  Block for 10 ticks if a
  // message is not immediately available.
  if( xQueueReceive( xQueue, &( pxRxedMessage ), ( portTickType ) 10 ) )
  {
   // pcRxedMessage now points to the struct AMessage variable posted
   // by vATask.
  }
 }

 // ... Rest of task code.
 }

xQueueGenericReceive

queue. h

 portBASE_TYPE xQueueGenericReceive(
            xQueueHandle xQueue,
            void *pvBuffer,
            portTickType xTicksToWait
            portBASE_TYPE xJustPeek
         ); 

It is preferred that the macro xQueueReceive() be used rather than calling this function directly.

Receive an item from a 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.

This function must not be used in an interrupt service routine. See xQueueReceiveFromISR for an alternative that can.

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.
xTicksToWait	The maximum amount of time the task should block waiting for an item to receive should the queue be empty at the time of the call. The time is defined in tick periods so the constant portTICK_RATE_MS should be used to convert to real time if this is required. xQueueGenericReceive() will return immediately if the queue is empty and xTicksToWait is 0.
xJustPeek	When set to true, the item received from the queue is not actually removed from the queue - meaning a subsequent call to xQueueReceive() will return the same item. When set to false, the item being received from the queue is also removed from the queue.

Returns:

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

Example usage:

 struct AMessage
 {
 char ucMessageID;
 char ucData[ 20 ];
 } xMessage;

 xQueueHandle xQueue;

 // Task to create a queue and post a value.
 void vATask( void *pvParameters )
 {
 struct AMessage *pxMessage;

 // Create a queue capable of containing 10 pointers to AMessage structures.
 // These should be passed by pointer as they contain a lot of data.
 xQueue = xQueueCreate( 10, sizeof( struct AMessage * ) );
 if( xQueue == 0 )
 {
  // Failed to create the queue.
 }

 // ...

 // Send a pointer to a struct AMessage object.  Don't block if the
 // queue is already full.
 pxMessage = & xMessage;
 xQueueSend( xQueue, ( void * ) &pxMessage, ( portTickType ) 0 );

 // ... Rest of task code.
 }

 // Task to receive from the queue.
 void vADifferentTask( void *pvParameters )
 {
 struct AMessage *pxRxedMessage;

 if( xQueue != 0 )
 {
  // Receive a message on the created queue.  Block for 10 ticks if a
  // message is not immediately available.
  if( xQueueGenericReceive( xQueue, &( pxRxedMessage ), ( portTickType ) 10 ) )
  {
   // pcRxedMessage now points to the struct AMessage variable posted
   // by vATask.
  }
 }

 // ... Rest of task code.
 }

uxQueueMessagesWaiting

queue. h

 unsigned portBASE_TYPE uxQueueMessagesWaiting( const xQueueHandle xQueue ); 

Return the number of messages stored in a queue.

Parameters:

xQueue

A handle to the queue being queried.

Returns:

The number of messages available in the queue.

vQueueDelete

queue. h

 void vQueueDelete( xQueueHandle xQueue ); 

Delete a queue - freeing all the memory allocated for storing of items placed on the queue.

Parameters:

xQueue

A handle to the queue to be deleted.

xQueueSendToFrontFromISR

queue. h

 portBASE_TYPE xQueueSendToFrontFromISR(
           xQueueHandle pxQueue,
           const void *pvItemToQueue,
           portBASE_TYPE *pxHigherPriorityTaskWoken
           );

This is a macro that calls xQueueGenericSendFromISR().

Post an item to the front of a queue. It is safe to use this macro from within an interrupt service routine.

Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued.

Parameters:

xQueue	The handle to the queue on which the item is to be posted.
pvItemToQueue	A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area.
pxHigherPriorityTaskWoken	xQueueSendToFrontFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueSendToFromFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited.

Returns:

pdTRUE if the data was successfully sent to the queue, otherwise errQUEUE_FULL.

Example usage for buffered IO (where the ISR can obtain more than one value per call):

 void vBufferISR( void )
 {
 char cIn;
 portBASE_TYPE xHigherPrioritTaskWoken;

 // We have not woken a task at the start of the ISR.
 xHigherPriorityTaskWoken = pdFALSE;

 // Loop until the buffer is empty.
 do
 {
  // Obtain a byte from the buffer.
  cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );

  // Post the byte.
  xQueueSendToFrontFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );

 } while( portINPUT_BYTE( BUFFER_COUNT ) );

 // Now the buffer is empty we can switch context if necessary.
 if( xHigherPriorityTaskWoken )
 {
  taskYIELD ();
 }
 }

xQueueSendToBackFromISR

queue. h

 portBASE_TYPE xQueueSendToBackFromISR(
           xQueueHandle pxQueue,
           const void *pvItemToQueue,
           portBASE_TYPE *pxHigherPriorityTaskWoken
           );

This is a macro that calls xQueueGenericSendFromISR().

Post an item to the back of a queue. It is safe to use this macro from within an interrupt service routine.

Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued.

Parameters:

xQueue	The handle to the queue on which the item is to be posted.
pvItemToQueue	A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area.
pxHigherPriorityTaskWoken	xQueueSendToBackFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueSendToBackFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited.

Returns:

pdTRUE if the data was successfully sent to the queue, otherwise errQUEUE_FULL.

Example usage for buffered IO (where the ISR can obtain more than one value per call):

 void vBufferISR( void )
 {
 char cIn;
 portBASE_TYPE xHigherPriorityTaskWoken;

 // We have not woken a task at the start of the ISR.
 xHigherPriorityTaskWoken = pdFALSE;

 // Loop until the buffer is empty.
 do
 {
  // Obtain a byte from the buffer.
  cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );

  // Post the byte.
  xQueueSendToBackFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );

 } while( portINPUT_BYTE( BUFFER_COUNT ) );

 // Now the buffer is empty we can switch context if necessary.
 if( xHigherPriorityTaskWoken )
 {
  taskYIELD ();
 }
 }

xQueueSendFromISR

queue. h

 portBASE_TYPE xQueueSendFromISR(
          xQueueHandle pxQueue,
          const void *pvItemToQueue,
          portBASE_TYPE *pxHigherPriorityTaskWoken
        );

This is a macro that calls xQueueGenericSendFromISR(). It is included for backward compatibility with versions of FreeRTOS.org that did not include the xQueueSendToBackFromISR() and xQueueSendToFrontFromISR() macros.

Post an item to the back of a queue. It is safe to use this function from within an interrupt service routine.

Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued.

Parameters:

xQueue	The handle to the queue on which the item is to be posted.
pvItemToQueue	A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area.
pxHigherPriorityTaskWoken	xQueueSendFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueSendFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited.

Returns:

pdTRUE if the data was successfully sent to the queue, otherwise errQUEUE_FULL.

Example usage for buffered IO (where the ISR can obtain more than one value per call):

 void vBufferISR( void )
 {
 char cIn;
 portBASE_TYPE xHigherPriorityTaskWoken;

 // We have not woken a task at the start of the ISR.
 xHigherPriorityTaskWoken = pdFALSE;

 // Loop until the buffer is empty.
 do
 {
  // Obtain a byte from the buffer.
  cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );

  // Post the byte.
  xQueueSendFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWoken );

 } while( portINPUT_BYTE( BUFFER_COUNT ) );

 // Now the buffer is empty we can switch context if necessary.
 if( xHigherPriorityTaskWoken )
 {
  // Actual macro used here is port specific.
  taskYIELD_FROM_ISR ();
 }
 }

xQueueGenericSendFromISR

queue. h

 portBASE_TYPE xQueueGenericSendFromISR(
             xQueueHandle pxQueue,
             const void *pvItemToQueue,
             portBASE_TYPE *pxHigherPriorityTaskWoken,
             portBASE_TYPE xCopyPosition
            );

It is preferred that the macros xQueueSendFromISR(), xQueueSendToFrontFromISR() and xQueueSendToBackFromISR() be used in place of calling this function directly.

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

Items are queued by copy not reference so it is preferable to only queue small items, especially when called from an ISR. In most cases it would be preferable to store a pointer to the item being queued.

Parameters:

xQueue	The handle to the queue on which the item is to be posted.
pvItemToQueue	A pointer to the item that is to be placed on the queue. The size of the items the queue will hold was defined when the queue was created, so this many bytes will be copied from pvItemToQueue into the queue storage area.
pxHigherPriorityTaskWoken	xQueueGenericSendFromISR() will set *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task to unblock, and the unblocked task has a priority higher than the currently running task. If xQueueGenericSendFromISR() sets this value to pdTRUE then a context switch should be requested before the interrupt is exited.
xCopyPosition	Can take the value queueSEND_TO_BACK to place the item at the back of the queue, or queueSEND_TO_FRONT to place the item at the front of the queue (for high priority messages).

Returns:

pdTRUE if the data was successfully sent to the queue, otherwise errQUEUE_FULL.

Example usage for buffered IO (where the ISR can obtain more than one value per call):

 void vBufferISR( void )
 {
 char cIn;
 portBASE_TYPE xHigherPriorityTaskWokenByPost;

 // We have not woken a task at the start of the ISR.
 xHigherPriorityTaskWokenByPost = pdFALSE;

 // Loop until the buffer is empty.
 do
 {
  // Obtain a byte from the buffer.
  cIn = portINPUT_BYTE( RX_REGISTER_ADDRESS );

  // Post each byte.
  xQueueGenericSendFromISR( xRxQueue, &cIn, &xHigherPriorityTaskWokenByPost, queueSEND_TO_BACK );

 } while( portINPUT_BYTE( BUFFER_COUNT ) );

 // Now the buffer is empty we can switch context if necessary.  Note that the
 // name of the yield function required is port specific.
 if( xHigherPriorityTaskWokenByPost )
 {
  taskYIELD_YIELD_FROM_ISR();
 }
 }

xQueueReceiveFromISR

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 )
 {
 char cValueToPost;
 const portTickType xBlockTime = ( portTickType )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 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;
 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 ();
 }
 }