FreeRTOS--XQueueReceiveFromISR

最新推荐文章于 2025-09-24 08:31:32 发布

转载最新推荐文章于 2025-09-24 08:31:32 发布 · 1w 阅读

文章标签：

#character #documentation #任务 #output #function #c

本文介绍FreeRTOS中xQueueReceiveFromISR函数的用法，该函数允许从中断服务程序安全地接收队列项目。文章详细解释了函数参数及返回值，并提供了创建队列、发送字符以及在中断服务程序中接收字符的示例。

XQueueReceiveFromISR-FreeRTOS API

portBASE_TYPE xQueueReceiveFromISR( xQueueHandle pxQueue, void pvBuffer, portBASE_TYPE pxTaskWoken );

从队列接收一个项目。在中断程序中使用此函数是安全的。

参数:

pxQueue	发送项目的队列句柄
pvBuffer	指向缓冲区的指针，将接收的项目被复制进去。
pxTaskWoken	任务将锁住，等待队列中的可用空间。如果xQueueReceiveFromISR 引起一个任务解锁，pxTaskWoken 将设置为pdTRUE，否则pxTaskWoken保留不变

返回:

pdTRUE ：如果项目成功从队列接收。否则为： pdFALSE

例子：

xQueueHandle xQueue;

// Function to create a queue and post some values. 
void vAFunction( void *pvParameters ) 
{ 
    portCHAR cValueToPost; 
    const portTickType xBlockTime = ( portTickType )0xff;

    // Create a queue capable of containing 10 characters. 
    xQueue = xQueueCreate( 10, sizeof( portCHAR ) ); 
    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; 
    portCHAR 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( xTaskWokenByPost != 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 (); 
    } 
}