3 Semaphores

Question 1

What are the advantages of task synchronisation?

Answer 1

Task Synchronisation makes it possible for tasks to co-ordinate and co-operate.
Can be used to communicate between tasks.
Can be used to protect shared data.

Question 2

Name the types of semaphores

Answer 2

Binary, counting, and mutex

Question 3

Describe binary semaphores

Answer 3

Binary - Implements synchronisation between tasks or between interrupt handlers and tasks. An attempt to take a semaphore will block unless the semaphore has been given by another task or interrupt handler.
Can be given infinite times but only taken once.

Question 4

Describe counting semaphores

Answer 4

Counting- Has a count variable associated with it.
Giving the semaphore increments the count
Taking the semaphore decrements the count
Can be used for counting events to ensure that no events lost.

Question 5

Describe a mutex

Answer 5

Mutex – Token used to guard a resource.
Only the task with mutex can access the resource.
When a mutex is taken, it must be given back

Question 6

How would you create a binary semaphore?

Answer 6

Define a variable of type SemaphoreHandle_t
SemaphoreHandle_t SW_Semaphore=NULL;,
SW_Semaphore = xSemaphoreCreateBinary();

Question 7

How do you give or take a semaphore?

Answer 7

xSeamphoreGive() and xSemaphoreTake()

Question 8

What is a deadlock?

Answer 8

A deadlock is where 2 tasks cannot proceed because they are both waiting on a resource held by the other.