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:
-
configSUPPORT_DYNAMIC_ALLOCATION
must be set to 1 in FreeRTOSConfig.h, or left undefined (in which case it will
default to 1).
-
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 depends on whether
configUSE_16_BIT_TICKS or configTICK_TYPE_WIDTH_IN_BITS is used to control the type of TickType_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 number of bits (or flags) implemented within an event group is 8 if configTICK_TYPE_WIDTH_IN_BITS is set to TICK_TYPE_WIDTH_16_BITS,
or 24 if configTICK_TYPE_WIDTH_IN_BITS is set to TICK_TYPE_WIDTH_32_BITS, or 56 if configTICK_TYPE_WIDTH_IN_BITS is set to TICK_TYPE_WIDTH_64_BITS.
The dependency on configUSE_16_BIT_TICKS or configTICK_TYPE_WIDTH_IN_BITS results from the data type used for thread local storage in the internal implementation of RTOS tasks.
-
Parameters:
-
-
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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