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xEventGroupSetBits()
[Event Group API]



event_groups.h

 EventBits_t xEventGroupSetBits( EventGroupHandle_t xEventGroup,
                                 const EventBits_t uxBitsToSet );

Set bits (flags) within an RTOS event group. This function cannot be called from an interrupt. xEventGroupSetBitsFromISR() is a version that can be called from an interrupt.

Setting bits in an event group will automatically unblock tasks that are blocked waiting for the bits.

The RTOS source file FreeRTOS/source/event_groups.c must be included in the build for the xEventGroupSetBits() function to be available.

Parameters:
xEventGroup   The event group in which the bits are to be set. The event group must have previously been created using a call to xEventGroupCreate().
uxBitsToSet   A bitwise value that indicates the bit or bits to set in the event group. For example, set uxBitsToSet to 0x08 to set only bit 3. Set uxBitsToSet to 0x09 to set bit 3 and bit 0.
Returns:
The value of the event group at the time the call to xEventGroupSetBits() returns.

There are two reasons why the returned value might have the bits specified by the uxBitsToSet parameter cleared:

  1. If setting a bit results in a task that was waiting for the bit leaving the blocked state then it is possible the bit will have been cleared automatically (see the xClearBitOnExit parameter of xEventGroupWaitBits()).

  2. Any unblocked (or otherwise Ready state) task that has a priority above that of the task that called xEventGroupSetBits() will execute and may change the event group value before the call to xEventGroupSetBits() returns.
Example usage:
#define BIT_0	( 1 << 0 )
#define BIT_4	( 1 << 4 )

void aFunction( EventGroupHandle_t xEventGroup )
{
EventBits_t uxBits;

  /* Set bit 0 and bit 4 in xEventGroup. */
  uxBits = xEventGroupSetBits(
                              xEventGroup,    /* The event group being updated. */
                              BIT_0 | BIT_4 );/* The bits being set. */

  if( ( uxBits & ( BIT_0 | BIT_4 ) ) == ( BIT_0 | BIT_4 ) )
  {
      /* Both bit 0 and bit 4 remained set when the function returned. */
  }
  else if( ( uxBits & BIT_0 ) != 0 )
  {
      /* Bit 0 remained set when the function returned, but bit 4 was
      cleared.  It might be that bit 4 was cleared automatically as a
      task that was waiting for bit 4 was removed from the Blocked
      state. */
  }
  else if( ( uxBits & BIT_4 ) != 0 )
  {
      /* Bit 4 remained set when the function returned, but bit 0 was
      cleared.  It might be that bit 0 was cleared automatically as a
      task that was waiting for bit 0 was removed from the Blocked
      state. */
  }
  else
  {
      /* Neither bit 0 nor bit 4 remained set.  It might be that a task
      was waiting for both of the bits to be set, and the bits were cleared
      as the task left the Blocked state. */
  }
}






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