Chapter 2. API Reference
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else
{
// The event group was created.
}
Return 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. See https://www.FreeRTOS.
org/a00111.html
EventGroupHandle_t xEventGroupCreateStatic(StaticEventGroup_t *pxEventGroupBuffer)
Create a new event group.
Internally, within the FreeRTOS implementation, event groups use a [small] block of memory, in which
the event group’s structure is stored. If an event groups is created using xEventGroupCreate() then the
required memory is automatically dynamically allocated inside the xEventGroupCreate() function. (see
https://www.FreeRTOS.org/a00111.html). If an event group is created using xEventGroupCreateStatic() then
the application writer must instead provide the memory that will get used by the event group. xEventGroupCre-
ateStatic() therefore allows an event group to be created without using any dynamic memory allocation.
Although event groups are not related to ticks, for internal implementation reasons the number of bits avail-
able for use in an event group is dependent on the configUSE_16_BIT_TICKS setting in FreeRTOSConfig.h.
If configUSE_16_BIT_TICKS is 1 then each event group contains 8 usable bits (bit 0 to bit 7). If confi-
gUSE_16_BIT_TICKS is set to 0 then each event group has 24 usable bits (bit 0 to bit 23). The EventBits_t
type is used to store event bits within an event group.
Example usage:
// StaticEventGroup_t is a publicly accessible structure that has the same
// size and alignment requirements as the real event group structure. It is
// provided as a mechanism for applications to know the size of the event
// group (which is dependent on the architecture and configuration file
// settings) without breaking the strict data hiding policy by exposing the
// real event group internals. This StaticEventGroup_t variable is passed
// into the xSemaphoreCreateEventGroupStatic() function and is used to store
// the event group's data structures
StaticEventGroup_t xEventGroupBuffer;
// Create the event group without dynamically allocating any memory.
xEventGroup = xEventGroupCreateStatic( &xEventGroupBuffer );
Return If the event group was created then a handle to the event group is returned. If pxEventGroupBuffer
was NULL then NULL is returned.
Parameters
• pxEventGroupBuffer: pxEventGroupBuffer must point to a variable of type StaticEvent-
Group_t, which will be then be used to hold the event group’s data structures, removing the need
for the memory to be allocated dynamically.
EventBits_t xEventGroupWaitBits(EventGroupHandle_t xEventGroup, const EventBits_t uxBit-
sToWaitFor, const BaseType_t xClearOnExit, const Base-
Type_t xWaitForAllBits, TickType_t xTicksToWait)
[Potentially] block to wait for one or more bits to be set within a previously created event group.
This function cannot be called from an interrupt.
Example usage:
#define BIT_0 ( 1 << 0 )
#define BIT_4 ( 1 << 4 )
void aFunction( EventGroupHandle_t xEventGroup )
{
EventBits_t uxBits;
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