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xEventGroupCreate()
[Event Group API]


event_groups.h

 EventGroupHandle_t xEventGroupCreate( void );

Creates a new RTOS event group, and returns a handle by which the newly created event group can be referenced.

For this RTOS API function to be available:

  1. configSUPPORT_DYNAMIC_ALLOCATION must be set to 1 in FreeRTOSConfig.h, or left undefined (in which case it will default to 1).
  2. The RTOS source file FreeRTOS/source/event_groups.c must be included in the build.

Each event group requires a [very] small amount of RAM that is used to hold the event group's state. If an event group is created using xEventGroupCreate() then the required RAM is automatically allocated from the FreeRTOS heap. If an event group is created using xEventGroupCreateStatic() then the RAM is provided by the application writer, which requires an additional parameter, but allows the RAM to be statically allocated at compile time. See the Static Vs Dynamic allocation page for more information.

Event groups are stored in variables of type EventBits_t. The number of bits (or flags) implemented within an event group is 8 if configUSE_16_BIT_TICKS is set to 1, or 24 if configUSE_16_BIT_TICKS is set to 0. The dependency on configUSE_16_BIT_TICKS results from the data type used for thread local storage in the internal implementation of RTOS tasks.

Parameters:
None  
Returns:
If the event group was created then a handle to the event group is returned. If there was insufficient FreeRTOS heap available to create the event group then NULL is returned.
Example usage:
    /* Declare a variable to hold the created event group. */
    EventGroupHandle_t xCreatedEventGroup;

    /* Attempt to create the event group. */
    xCreatedEventGroup = xEventGroupCreate();

    /* Was the event group created successfully? */
    if( xCreatedEventGroup == NULL )
    {
        /* The event group was not created because there was insufficient
        FreeRTOS heap available. */
    }
    else
    {
        /* The event group was created. */
    }






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