Quality RTOS & Embedded Software

 Real time embedded FreeRTOS RSS feed 
Quick Start Supported MCUs PDF Books Trace Tools Ecosystem TCP & FAT Training




xQueueOverwrite
[Queue Management]

queue.h
BaseType_t xQueueOverwrite( QueueHandle_t xQueue, const void * pvItemToQueue );

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

A version of xQueueSendToBack() that will write to the queue even if the queue is full, overwriting data that is already held in the queue.

xQueueOverwrite() is intended for use with queues that have a length of one, meaning the queue is either empty or full.

This function must not be called from an interrupt service routine (ISR). See xQueueOverwriteFromISR() for an alternative which may be used in an ISR.

Parameters:
xQueue   The handle of the queue to which the data is to be sent.
pvItemToQueue   A pointer to the item that is to be placed in the queue. The size of the items the queue will hold was defined when the queue was created, and that many bytes will be copied from pvItemToQueue into the queue storage area.
Returns:
xQueueOverwrite() is a macro that calls xQueueGenericSend(), and therefore has the same return values as xQueueSendToFront(). However, pdPASS is the only value that can be returned because xQueueOverwrite() will write to the queue even when the queue was already full.
Example usage:
 void vFunction( void *pvParameters )
 {
 QueueHandle_t xQueue;
 unsigned long ulVarToSend, ulValReceived;

    /* Create a queue to hold one unsigned long value.  It is strongly
    recommended *not* to use xQueueOverwrite() on queues that can
    contain more than one value, and doing so will trigger an assertion
    if configASSERT() is defined. */
    xQueue = xQueueCreate( 1, sizeof( unsigned long ) );

    /* Write the value 10 to the queue using xQueueOverwrite(). */
    ulVarToSend = 10;
    xQueueOverwrite( xQueue, &ulVarToSend );

    /* Peeking the queue should now return 10, but leave the value 10 in
    the queue.  A block time of zero is used as it is known that the
    queue holds a value. */
    ulValReceived = 0;
    xQueuePeek( xQueue, &ulValReceived, 0 );

    if( ulValReceived != 10 )
    {
        /* Error, unless another task removed the value. */
    }

    /* The queue is still full.  Use xQueueOverwrite() to overwrite the
    value held in the queue with 100. */
    ulVarToSend = 100;
    xQueueOverwrite( xQueue, &ulVarToSend );

    /* This time read from the queue, leaving the queue empty once more.
    A block time of 0 is used again. */
    xQueueReceive( xQueue, &ulValReceived, 0 );

    /* The value read should be the last value written, even though the
    queue was already full when the value was written. */
    if( ulValReceived != 100 )
    {
        /* Error unless another task is using the same queue. */
    }

    /* ... */
}





[ Back to the top ]    [ About FreeRTOS ]    [ Sitemap ]    [ ]




Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.

Latest News

FreeRTOS kernel V10 is available for immediate download. Now MIT licensed.


FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

IAR Partner

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers

STMicro RTOS partner supporting ARM7, ARM Cortex-M3, ARM Cortex-M4 and ARM Cortex-M0

Texas Instruments MCU Developer Network RTOS partner for ARM and MSP430 microcontrollers

OpenRTOS and SafeRTOS