4 Event Groups

Question 1

What is an event group?

Answer 1

An event group is a group of bits or flags. An event group allows a task to be in a blocked state until an event or combination of event occur.

Question 2

Why are event flags used?

Answer 2

An event flag is used to indicate if an event has occurred or not.

Question 3

How many event flags can an event group store?

Answer 3

24, bits 0 to 23.

Question 4

What is the difference between an event group and semaphore when unblocking tasks?

Answer 4

Event groups can unblock multiple tasks, a semaphore can only unblock a single task.
A semaphore allows a task to wait in a blocked state until a single event occurs.

Question 5

What advantages does an event group have over a semaphore?

Answer 5

Can synchronise multiple task,
It can unblock multiple tasks,
Allow a task to remain in a blocked state until a combination of events occur,
An event group uses less RAM then multiple binary semaphores.

Question 6

How do you create an event group?

Answer 6

Declare an event group variable:
EventGroupHandle_t SW_EventGroup = NULL;
Create the event group in main()
SW_EventGroup = xEventGroupCreate();

Question 7

How do you set an event group bit(s)?

Answer 7

define BIT0 (1«0)

xEventGroupSetBits(SW_EventGroup, BIT0)

For Multiple Bits
xEventGroupSetBits(SW_EventGroup, BIT0 | BIT1)

Question 8

How to wait on event group bit(s)?

Answer 8

xEventGroupWaitBits(SW_EventGroup, BIT0, pdTrue, pdFalse, portMAX_DELAY)