What are atomic instructions

 Execute as a single uninterrupted unit 

Why is an idle task required in RTOS

1. System stability

Refraining from keeping the system without any task running

2. Power management 

Idle task can be used to implement low power or sleep functions

3. Resource management 

Idle task can be used to implement memory freeing functions and other maintenance activities 

What is a Race condition

 In parallel programming, if 2 threads try to access the same shared resource simultaneously then this can lead to unpredictable behaviour or errors this is called race condition

What is the default scheduling mechanism of FreeRTOS

 The default scheduling is preemptive priority based.

What are spin locks in freeRTOS

 Spin locks are used for synchronization, the task trying to acquire the lock goes into a tight polling loop (busy wait loop )continuously checking if the lock is available 

What is the lowest priority that can be set in an arm cortex M processors

n the ARM cortex M processors the priority is defined using 4 bits and hence the lowest priority is 15(0xF)

Deleting a task in freeRTOS

Function used to delete a task is vDeleteTask() - this function only marks the task as deleted 

The work of freeing the memory from a deleted task is done by the ideal task 

In real world we donot delete a task very often. If we donot need a task we either send it to a suspended mode or a blocked state

Real Time Systems

  We define a system as real time if there is a small and bounded delay between the time when the task should be completed amd when it is actually completed.

An operating system layer is between the application software and hardware

Real time operating system

A real time operating system is a software that manages system resources such as I/O,memory,data and processors guaranteeing that all Timming constraints are satisfied and provides reliable operations.

It also handles the synchronisation and assigning tasks across distributed processes

They should be simple so they may be predictable.

Hardware abraction layer(HAL) libraries when added to an operating system simplfies the porting of the application code from one MCU to another.

Features of Real Time Operating Systems

Evolution is the process of system changing to improve performance,features and reliability

An RTOS must manage change.

Portability is the ease at which one system can be changed or adapted to create another system.

While designing a new system it is a good de esigning practice to build a new system by changing an existing one.

Latency or response time is the delay from the request to the beginning of the service of that request.

Bandwidth is the number of information bytes/second that can be transferred or processed