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Write a note on Message Queues, Mailboxes, Pipes, Semaphores, Datatypes
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Message Queue

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

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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.

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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'.

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(ii) Counting semaphores

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

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

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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

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