Message Queue

A buffer like data structure through tasks and ISRs communicating with each other by sending and receiving message and sync with data.

Mailboxes

• Mailboxes are much similar to message queues.

• used for one way messaging.

• Function of RTOS - to create, to write, to read from the mailbox and to destroy it if no longer needed.

Pipes

• are objects created for unstructured data exchange between tasks and facilitate sync among tasks.

• unidirectional data exchange.

When pipe is created, 2 descriptors are created.

Semaphore

• A kernel object which is used for coordinating or sync activities in which multiple tasks tries to acquire same resource.

• used to control the access of shared resource to one task out of multiple.

• Thus - semaphore - acts as key.

(i) Binary semaphores

• simple '0' and '1' $\to$ key available or not

• used in cases where only one task can access the given shared resource.

• tasks $\to$ resource $\to$ check semaphore

$\to$ if '1' - available $\to$ task access the shared resource making semaphore '0'.

(ii) Counting semaphores

$\to$ Resource is accessed by multiple tasks at a given time.

$\to$ n tasks can access the shared resource.

Mutual exclusion(Mutex semaphore)

Datatypes

char $\to$ 1 Byte $\;\;\;\;\;\;$ (-127 to 128)

signed $\to$ 1 Byte $\;\;\;\;$ (-127 to 128)

unsigned $\to$ 1 Byte $\;$ (0 to 255)

int $\to$ 2 Byte $\;\;\;\;\;\;\;\;$ (-32768 to 32767)

signed $\to$ 2 Byte

unsigned $\to$ 2 Byte

short int $\to$ 2 Byte

long int $\to$ 4 Byte

float $\to$ 4 Byte

double $\to$ 8 Byte

long $\to$ 10 Byte