queue. h
QueueHandle_t xQueueCreate( UBaseType_t uxQueueLength,
UBaseType_t uxItemSize );
Creates a new queue and returns a
handle by which the queue can be referenced.
configSUPPORT_DYNAMIC_ALLOCATION
must be set to 1 in FreeRTOSConfig.h, or left undefined (in which case it will
default to 1), for this RTOS API function to be available.
Each queue requires RAM that is used to hold the queue state, and to hold the
items that are contained in the queue (the queue storage area).
If a queue is created using xQueueCreate() then the required RAM is automatically
allocated from the FreeRTOS heap.
If a queue is created using xQueueCreateStatic()
then the RAM is provided by the application writer, which results in a greater
number of parameters, but allows the RAM to be statically allocated at compile
time. See the Static Vs
Dynamic allocation page for more information.
-
Parameters:
-
uxQueueLength
|
The maximum number of items the queue can hold at any one
time.
|
uxItemSize
|
The size, in bytes, required to hold each item in the queue.
Items are queued by copy, not by reference, so this is the number of bytes
that will be copied for each queued item. Each item in the queue
must be the same size.
|
-
Returns:
-
If the queue is created successfully then a handle to the created queue
is returned. If the memory required to create the queue could not be
allocated then NULL is returned.
Example usage:
struct AMessage
{
char ucMessageID;
char ucData[ 20 ];
};
void vATask( void *pvParameters )
{
QueueHandle_t xQueue1, xQueue2;
/* Create a queue capable of containing 10 unsigned long values. */
xQueue1 = xQueueCreate( 10, sizeof( unsigned long ) );
if( xQueue1 == NULL )
{
/* Queue was not created and must not be used. */
}
/* Create a queue capable of containing 10 pointers to AMessage
structures. These are to be queued by pointers as they are
relatively large structures. */
xQueue2 = xQueueCreate( 10, sizeof( struct AMessage * ) );
if( xQueue2 == NULL )
{
/* Queue was not created and must not be used. */
}
/* ... Rest of task code. */
}
Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.