RTOS

Question 1

what is a system?

Answer 1

Something that solves a problem

Question 2

What is a task?

Answer 2

Group of instructions that execute on a micro-controller to solve a portion of the problem. System may have multiple tasks running at one time.

Question 3

multitasking?

Answer 3

doing multiple things at once

Question 4

Deadline

Answer 4

Most essential aspect.

tasks has to perform their function within a prescribed deadline.

Question 5

What types of deadlines are there?

Answer 5

Absolute deadlines(hard real time system)
Relaxed(soft real time system)-tasks don't have rigid time constraints.

Question 6

What is Priority?

Answer 6

Determines the importance of a task in a system. Important tasks have higher priority

Question 7

What is Preemption?

Answer 7

Higher priority tasks perform their tasks before low priority tasks

Question 8

What is a Scheduler?

Answer 8

Decides which tasks runs at what time.

Question 9

What are the two types of RTOS?

Answer 9

Even Driven Systems and Time Sharing Systems

Question 10

What is an event driven system?

Answer 10

Its a system which swiches between tasks based on priorities

Question 11

What is a time sharing system?

Answer 11

A system that switches tasks based on clock interrupts

Question 12

What is Jitter?

Answer 12

the variability in time that it takes to accept and complete a task

Question 13

what does it mean to switch tasks?

Answer 13

Also called context switching. Its when you restore the state of a process so that execution can be resumed from the same point at a later time.

Question 14

What is preemptive priority

Answer 14

Also called priority scheduling. Act of temporarily interrupting a task being carried out with the intention of resuming the task later.

Question 15

What 3 states does a task have?

Answer 15

Running(being executed on CPU)
Ready(Ready to be executed)
Blocked(Waiting for an event)

Question 16

It is unsafe for two tasks to access the same specific data or hardware resource simultaneously. What are the three common approaches to solving this problem?

Answer 16

Temporarily Masking/Disabling Interrupts

Binary Semaphores

Message Passing

Question 17

What are binary semaphores

Answer 17

variable or abstract data type that is used to control access to a common resource

Question 18

kernel?

Answer 18

computer program that has complete control over everything that occurs in the computers operating system

Question 19

What is a process?

Answer 19

A program that has sole control over some system resources
Processes can’t directly share its resources and so are protected from each other.
e.g. main()

Question 20

what is a thread of execution?

Answer 20

smallest sequence of programmed instructions that can be managed independently by a scheduler.
Threads are inside the process.

Threads are created from within a process

Question 21

What does it mean when we say processes are hostile to each other?

Answer 21

Each process has a different owner.

Has its own address space, global variables, open files and signals and semaphores

Question 22

What does it mean when we say processes are hostile to each other?

Answer 22

Each process has a different owner.

Has its own address space, global variables, open files and signals and semaphores

Question 23

Difference between processes and threads

Answer 23

Threads cooperate with each other

has the sam eowner

Question 24

What are the different structures for multitasking?

Answer 24

1. Sequential execution (superloop)
2. Timed super loop
3. Backround/foreground-interrupts
4. Schedulers of various types

Question 25

What is the super loop structure?

Answer 25

It simply loops endlessly Loop Execution time isn't constant Tasks BLOCK EACH OTHER. A task that is ready to execute has to wait for the one before it to finish There isn't a task prioritisation mechanism to give higher priority tasks more time

Question 26

what is the timed super loop structure

Answer 26

adding a hardware timer tick to the superloop structure At least one task with execute regularly. Measured in real time STILL, processor time is wasted when you're waiting, tasks block each other and theres no prioritisation

Question 27

What is the Foreground/Background Structure?

Answer 27

Interrupts are added to allow for prioritisation the superloop is in the background while the higher priority tasks are brought to the foreground. Foreground tasks are often event driven.

Question 28

What is general OS structure?

Answer 28

Requires one task counter for each task, counters allow tasks to run at different rates Background tasks still block tasks can be enabled/disabled

Question 29

What is the simplest scheduler?

Answer 29

Cycling scheduling. Same as super loop

Question 30

What is Round Robin Scheduling?

Answer 30

System driven by a periodic interrupt. like the clock tick super loop

Question 31

What is prioritised preemptive scheduling

Answer 31

High Priority tasks complete before any time is allocated to lower priority tasks. This is classical RTOS

Question 32

What is Cooperative Scheduling?

Answer 32

It can control its own context switching so it minimises excess computation time.