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Richard Barry 2013-07-19 09:16:36 +00:00
parent 203ae64600
commit 08057fa77f
1 changed files with 26 additions and 16 deletions
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42
FreeRTOS/Source/include/queue.h
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@ -420,19 +420,20 @@ typedef void * xQueueSetMemberHandle;
* <pre>
portBASE_TYPE xQueueOverwrite(
xQueueHandle xQueue,
const void * pvItemToQueue,
const void * pvItemToQueue
);
* </pre>
*
* Only for use with queues that can hold a single item - so the queue is either
* Only for use with queues that have a length of one - so the queue is either
* empty or full.
*
* Post an item on a queue. If the queue is already full then overwrite the
* value held in the queue. The item is queued by copy, not by reference.
*
* This function must not be called from an interrupt service routine.
* See xQueueOverwriteFromISR () for an alternative which may be used in an ISR.
*
* @param xQueue The handle to the queue on which the item is to be posted.
* @param xQueue The handle of the queue to which the data is being sent.
*
* @param pvItemToQueue A pointer to the item that is to be placed on the
* queue. The size of the items the queue will hold was defined when the
@ -440,9 +441,9 @@ typedef void * xQueueSetMemberHandle;
* into the queue storage area.
*
* @return xQueueOverwrite() is a macro that calls xQueueGenericSend(), and
* therefore has the same return values as xQueueSendToFront(). However, as
* xQueueOverwrite() will write to the queue even when the queue is full pdPASS
* will be returned in all cases (errQUEUE_FULL will never be returned).
* 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 is already full.
*
* Example usage:
<pre>
@ -470,7 +471,7 @@ typedef void * xQueueSetMemberHandle;
if( ulValReceived != 10 )
{
// Error!
// Error unless the item was removed by a different task.
}
// The queue is still full. Use xQueueOverwrite() to overwrite the
@ -1086,7 +1087,7 @@ void vQueueDelete( xQueueHandle xQueue ) PRIVILEGED_FUNCTION;
);
* </pre>
*
* A version of xQueueOverwrite() that can be used from an interrupt service
* A version of xQueueOverwrite() that can be used in an interrupt service
* routine (ISR).
*
* Only for use with queues that can hold a single item - so the queue is either
@ -1105,14 +1106,14 @@ void vQueueDelete( xQueueHandle xQueue ) PRIVILEGED_FUNCTION;
* @param pxHigherPriorityTaskWoken xQueueOverwriteFromISR() will set
* *pxHigherPriorityTaskWoken to pdTRUE if sending to the queue caused a task
* to unblock, and the unblocked task has a priority higher than the currently
* running task. If xQueueSendFromISR() sets this value to pdTRUE then
* running task. If xQueueOverwriteFromISR() sets this value to pdTRUE then
* a context switch should be requested before the interrupt is exited.
*
* @return xQueueOverwriteFromISR() is a macro that calls
* xQueueGenericSendFromISR(), and therefore has the same return values as
* xQueueSendToFrontFromISR(). However, as xQueueOverwriteFromISR() will write
* to the queue even when the queue is full pdPASS will be returned in all cases
* (errQUEUE_FULL will never be returned).
* @return xQueueOverwriteFromISR() is a macro that calls
* xQueueGenericSendFromISR(), and therefore has the same return values as
* xQueueSendToFrontFromISR(). However, pdPASS is the only value that can be
* returned because xQueueOverwriteFromISR() will write to the queue even when
* the queue is already full.
*
* Example usage:
<pre>
@ -1122,7 +1123,7 @@ void vQueueDelete( xQueueHandle xQueue ) PRIVILEGED_FUNCTION;
void vFunction( void *pvParameters )
{
// Create a queue to hold one unsigned long value. It is strongly
// recommended *not* to use xQueueOverwrite() on queues that can
// recommended *not* to use xQueueOverwriteFromISR() 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 ) );
@ -1142,11 +1143,20 @@ unsigned long ulVarToSend, ulValReceived;
// pass because the value held in the queue will be overwritten with the
// new value.
ulVarToSend = 100;
xQueueOverwrite( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken );
xQueueOverwriteFromISR( xQueue, &ulVarToSend, &xHigherPriorityTaskWoken );
// Reading from the queue will now return 100.
// ...
if( xHigherPrioritytaskWoken == pdTRUE )
{
// Writing to the queue caused a task to unblock and the unblocked task
// has a priority higher than or equal to the priority of the currently
// executing task (the task this interrupt interrupted). Perform a context
// switch so this interrupt returns directly to the unblocked task.
portYIELD_FROM_ISR(); // or portEND_SWITCHING_ISR() depending on the port.
}
}
</pre>
* \defgroup xQueueOverwriteFromISR xQueueOverwriteFromISR