本帖最后由 会飞的猪_2020 于 2024-3-26 10:08 编辑
看到freertos里面的消息通知方式有，notify，eventgroup，queue，semaphore。不清楚它们的区别是什么啊。
所以昨天开始去读信号量的源代码，发现他这个怎么没有.c文件，里面貌似是用queue实现的，然后就从最开始的queue.c这个源文件看起。
个人的理解如下，可能有错误。
队列的动态创建方法如下：
[C] 纯文本查看 复制代码 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. */
}
我们看xQueueCreate的实现：
[C] 纯文本查看 复制代码 #if( configSUPPORT_DYNAMIC_ALLOCATION == 1 )
QueueHandle_t xQueueGenericCreate( const UBaseType_t uxQueueLength, const UBaseType_t uxItemSize, const uint8_t ucQueueType )
{
Queue_t *pxNewQueue;
size_t xQueueSizeInBytes;
uint8_t *pucQueueStorage;
configASSERT( uxQueueLength > ( UBaseType_t ) 0 );
if( uxItemSize == ( UBaseType_t ) 0 )
{
/* There is not going to be a queue storage area. */
xQueueSizeInBytes = ( size_t ) 0;
}
else
{
/* Allocate enough space to hold the maximum number of items that
can be in the queue at any time. */
xQueueSizeInBytes = ( size_t ) ( uxQueueLength * uxItemSize ); /*lint !e961 MISRA exception as the casts are only redundant for some ports. */
}
pxNewQueue = ( Queue_t * ) pvPortMalloc( sizeof( Queue_t ) + xQueueSizeInBytes );
if( pxNewQueue != NULL )
{
/* Jump past the queue structure to find the location of the queue
storage area. */
pucQueueStorage = ( ( uint8_t * ) pxNewQueue ) + sizeof( Queue_t );
#if( configSUPPORT_STATIC_ALLOCATION == 1 )
{
/* Queues can be created either statically or dynamically, so
note this task was created dynamically in case it is later
deleted. */
pxNewQueue->ucStaticallyAllocated = pdFALSE;
}
#endif /* configSUPPORT_STATIC_ALLOCATION */
prvInitialiseNewQueue( uxQueueLength, uxItemSize, pucQueueStorage, ucQueueType, pxNewQueue );
}
else
{
traceQUEUE_CREATE_FAILED( ucQueueType );
}
return pxNewQueue;
}
#endif /* configSUPPORT_STATIC_ALLOCATION */
结合网络上一张图，这个queue的结构体图示如下：
左边的是XQUEUE，右边的是pucQueueStorage
如果是动态申请的，这两片内存是连在一起的，只是pcHead去指向了pucQueueStorage：
从下面这行代码就可以看出，malloc的时候申请了"queue_t + xQueueSizeInBytes"的大小
[C] 纯文本查看 复制代码 pxNewQueue = ( Queue_t * ) pvPortMalloc( sizeof( Queue_t ) + xQueueSizeInBytes );
然后
[C] 纯文本查看 复制代码 pucQueueStorage = ( ( uint8_t * ) pxNewQueue ) + sizeof( Queue_t );
所以申请的的那个pxNewQueue,前面是XQUEUE，后面是pucQueueStorage
prvInitialiseNewQueue初始化了queue。
[C] 纯文本查看 复制代码 /*-----------------------------------------------------------*/
static void prvInitialiseNewQueue( const UBaseType_t uxQueueLength, const UBaseType_t uxItemSize, uint8_t *pucQueueStorage, const uint8_t ucQueueType, Queue_t *pxNewQueue )
{
/* Remove compiler warnings about unused parameters should
configUSE_TRACE_FACILITY not be set to 1. */
( void ) ucQueueType;
if( uxItemSize == ( UBaseType_t ) 0 )
{
/* No RAM was allocated for the queue storage area, but PC head cannot
be set to NULL because NULL is used as a key to say the queue is used as
a mutex. Therefore just set pcHead to point to the queue as a benign
value that is known to be within the memory map. */
pxNewQueue->pcHead = ( int8_t * ) pxNewQueue;
}
else
{
/* Set the head to the start of the queue storage area. */
pxNewQueue->pcHead = ( int8_t * ) pucQueueStorage;
}
/* Initialise the queue members as described where the queue type is
defined. */
pxNewQueue->uxLength = uxQueueLength;
pxNewQueue->uxItemSize = uxItemSize;
( void ) xQueueGenericReset( pxNewQueue, pdTRUE );
#if ( configUSE_TRACE_FACILITY == 1 )
{
pxNewQueue->ucQueueType = ucQueueType;
}
#endif /* configUSE_TRACE_FACILITY */
#if( configUSE_QUEUE_SETS == 1 )
{
pxNewQueue->pxQueueSetContainer = NULL;
}
#endif /* configUSE_QUEUE_SETS */
traceQUEUE_CREATE( pxNewQueue );
}
/*-----------------------------------------------------------*/
结合上面那张结构体的图片，应该很好理解上面的代码的意思。
xQueueGenericReset 代码如下：
[C] 纯文本查看 复制代码 BaseType_t xQueueGenericReset( QueueHandle_t xQueue, BaseType_t xNewQueue )
{
Queue_t * const pxQueue = ( Queue_t * ) xQueue;
configASSERT( pxQueue );
taskENTER_CRITICAL();
{
pxQueue->pcTail = pxQueue->pcHead + ( pxQueue->uxLength * pxQueue->uxItemSize );
pxQueue->uxMessagesWaiting = ( UBaseType_t ) 0U;
pxQueue->pcWriteTo = pxQueue->pcHead;
pxQueue->u.pcReadFrom = pxQueue->pcHead + ( ( pxQueue->uxLength - ( UBaseType_t ) 1U ) * pxQueue->uxItemSize );
pxQueue->cRxLock = queueUNLOCKED;
pxQueue->cTxLock = queueUNLOCKED;
if( xNewQueue == pdFALSE )
{
/* If there are tasks blocked waiting to read from the queue, then
the tasks will remain blocked as after this function exits the queue
will still be empty. If there are tasks blocked waiting to write to
the queue, then one should be unblocked as after this function exits
it will be possible to write to it. */
if( listLIST_IS_EMPTY( &( pxQueue->xTasksWaitingToSend ) ) == pdFALSE )
{
if( xTaskRemoveFromEventList( &( pxQueue->xTasksWaitingToSend ) ) != pdFALSE )
{
queueYIELD_IF_USING_PREEMPTION();
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
mtCOVERAGE_TEST_MARKER();
}
}
else
{
/* Ensure the event queues start in the correct state. */
vListInitialise( &( pxQueue->xTasksWaitingToSend ) );
vListInitialise( &( pxQueue->xTasksWaitingToReceive ) );
}
}
taskEXIT_CRITICAL();
/* A value is returned for calling semantic consistency with previous
versions. */
return pdPASS;
}
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发表于 2024-3-26 10:02:41
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