xQueueCreateStatic

Collaboration diagram for xQueueCreateStatic:

queue. h

QueueHandle_t xQueueCreateStatic(
                           UBaseType_t uxQueueLength,
                           UBaseType_t uxItemSize,
                           uint8_t *pucQueueStorage,
                           StaticQueue_t *pxQueueBuffer
                       );

Creates a new queue instance, and returns a handle by which the new queue can be referenced.

Internally, within the FreeRTOS implementation, queues use two blocks of memory. The first block is used to hold the queue's data structures. The second block is used to hold items placed into the queue. If a queue is created using xQueueCreate() then both blocks of memory are automatically dynamically allocated inside the xQueueCreate() function. (see https://www.FreeRTOS.org/a00111.html). If a queue is created using xQueueCreateStatic() then the application writer must provide the memory that will get used by the queue. xQueueCreateStatic() therefore allows a queue to be created without using any dynamic memory allocation.

https://www.FreeRTOS.org/Embedded-RTOS-Queues.html

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.
pucQueueStorage	If uxItemSize is not zero then pucQueueStorage must point to a uint8_t array that is at least large enough to hold the maximum number of items that can be in the queue at any one time - which is ( uxQueueLength * uxItemsSize ) bytes. If uxItemSize is zero then pucQueueStorage can be NULL.
pxQueueBuffer	Must point to a variable of type StaticQueue_t, which will be used to hold the queue's data structure.

Returns

If the queue is created then a handle to the created queue is returned. If pxQueueBuffer is NULL then NULL is returned.

Example usage:

  struct AMessage
  {
   char ucMessageID;
   char ucData[ 20 ];
  };
 
#define QUEUE_LENGTH 10
#define ITEM_SIZE sizeof( uint32_t )
 
  // xQueueBuffer will hold the queue structure.
  StaticQueue_t xQueueBuffer;
 
  // ucQueueStorage will hold the items posted to the queue.  Must be at least
  // [(queue length) * ( queue item size)] bytes long.
  uint8_t ucQueueStorage[ QUEUE_LENGTH * ITEM_SIZE ];
 
  void vATask( void *pvParameters )
  {
   QueueHandle_t xQueue1;
 
   // Create a queue capable of containing 10 uint32_t values.
   xQueue1 = xQueueCreate( QUEUE_LENGTH, // The number of items the queue can hold.
                           ITEM_SIZE     // The size of each item in the queue
                           &( ucQueueStorage[ 0 ] ), // The buffer that will hold the items in the queue.
                           &xQueueBuffer ); // The buffer that will hold the queue structure.
 
   // The queue is guaranteed to be created successfully as no dynamic memory
   // allocation is used.  Therefore xQueue1 is now a handle to a valid queue.
 
   // ... Rest of task code.
  }