Free RTOS inter task communication

Inter Task Communication

q  Queue management

q  Resources management

Queue management

Ø  Queues are the primary form of inter task

Communications

Ø  They can be used to send messages between tasks,

 and between interrupts and tasks

Ø  Queues are kind of pipes to transfer data between tasks in RTOS

Reading in a queue

Writing to a queue

Creating a queue

uxQueueLength:

The maximum number of items that the queue being created can hold at any one time.

uxItemSize:

The size in bytes of each data item that can be stored in the queue

Resources management

q  Semaphore

q  Mutex

Semaphores

Binary semaphores:

Ø  Binary semaphore can be seen as a queue which contains only one element

Ø  simple on/off mechanism

Counting Semaphores:

Ø  counting semaphores can be thought of as queues of length greater than one

Ø  Counting semaphores are typically used for two things:

1.Counting events, 2.Resource management

Binary semaphore Vs Counting Semaphore

Mutual Exclusion(Mutex)

Ø  Mutexes are binary semaphores that include a priority inheritance mechanism

Ø  Mutex acts like a token that is used to guard a resource

xSemaphoreHandle xSemaphoreCreateMutex( void );