Chapter 2. API Reference
(continued from previous page)
BIT_0 | BIT_4 ); // The bits being set.
if( xResult == pdPASS )
{
// The message was posted successfully.
}
}
Return If the request to execute the function was posted successfully then pdPASS is returned, otherwise
pdFALSE is returned. pdFALSE will be returned if the timer service queue was full.
Parameters
• xEventGroup: The event group in which the bits are to be cleared.
• uxBitsToClear: A bitwise value that indicates the bit or bits to clear. For example, to clear bit
3 only, set uxBitsToClear to 0x08. To clear bit 3 and bit 0 set uxBitsToClear to 0x09.
xEventGroupSetBitsFromISR(xEventGroup, uxBitsToSet, pxHigherPriorityTaskWoken)
A version of xEventGroupSetBits() that can be called from an interrupt.
Setting bits in an event group is not a deterministic operation because there are an unknown number of tasks
that may be waiting for the bit or bits being set. FreeRTOS does not allow nondeterministic operations to be
performed in interrupts or from critical sections. Therefore xEventGroupSetBitsFromISR() sends a message
to the timer task to have the set operation performed in the context of the timer task - where a scheduler lock
is used in place of a critical section.
Example usage:
#define BIT_0 ( 1 << 0 )
#define BIT_4 ( 1 << 4 )
// An event group which it is assumed has already been created by a call to
// xEventGroupCreate().
EventGroupHandle_t xEventGroup;
void anInterruptHandler( void )
{
BaseType_t xHigherPriorityTaskWoken, xResult;
// xHigherPriorityTaskWoken must be initialised to pdFALSE.
xHigherPriorityTaskWoken = pdFALSE;
// Set bit 0 and bit 4 in xEventGroup.
xResult = xEventGroupSetBitsFromISR(
xEventGroup, // The event group being updated.
BIT_0 | BIT_4 // The bits being set.
&xHigherPriorityTaskWoken );
// Was the message posted successfully?
if( xResult == pdPASS )
{
// If xHigherPriorityTaskWoken is now set to pdTRUE then a context
// switch should be requested. The macro used is port specific and
// will be either portYIELD_FROM_ISR() or portEND_SWITCHING_ISR() -
// refer to the documentation page for the port being used.
portYIELD_FROM_ISR( xHigherPriorityTaskWoken );
}
}
Return If the request to execute the function was posted successfully then pdPASS is returned, otherwise
pdFALSE is returned. pdFALSE will be returned if the timer service queue was full.
Parameters
• xEventGroup: The event group in which the bits are to be set.
• uxBitsToSet: A bitwise value that indicates the bit or bits to set. For example, to set bit 3 only,
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