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xQueueReceiveFromISR
[队列管理]

queue. h
BaseType_t xQueueReceiveFromISR ( QueueHandle_t xQueue, void *pvBuffer, BaseType_t *pxHigherPriorityTaskWoken );

从队列中接收项目。从中断服务程序内使用此函数是安全的。

参数:
xQueue 要从中接收项目的队列的句柄。
pvBuffer 指向缓冲区的指针,接收到的项目将被复制到这个缓冲区。
pxHigherPriorityTaskWoken 任务可被阻塞,以等待队列可用空间。如果 xQueueReceiveFromISR 使得此类任务阻塞解除,*pxHigherPriorityTaskWoken 将设置为 pdTRUE,否则 *pxHigherPriorityTaskWoken 将保持不变。

从 FreeRTOSV7.3.0 开始,pxHigherPriorityTaskWoken 是一个可选参数,可设置为 NULL。

返回:
如果从队列成功接收到项目,返回 pdTRUE,否则返回 pdFALSE。
示例用法:
QueueHandle_t xQueue;

/* Function to create a queue and post some values. */
void vAFunction( void *pvParameters )
{
char cValueToPost;
const TickType_t xTicksToWait = ( TickType_t )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 xTicksToWait ticks. */
    cValueToPost = 'a';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );
    cValueToPost = 'b';
    xQueueSend( xQueue, ( void * ) &cValueToPost, xTicksToWait );

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

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

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

    if( xTaskWokenByReceive != 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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