1. REAL TIME OPERATING SYSTEM
VIVEK JAISWAL
EC VI B
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2. Operating System
Collection of system calls (functions)
Provides a set of basic services to interact with the hardware
Core of the OS is Kernel
Basic structural unit of OS
Typically a library or set of libraries
Operates in supervisory mode
What is the project about?
Define the goal of this project
Is it similar to projects in the past or is it a new effort?
Define the scope of this project
Is it an independent project or is it related to other projects?
* Note that this slide is not necessary for weekly status meetings

3. Basic Structure of Operating System
Application Software
Application Programming Interface (API)
System Software
OS interface OS
Hardware OS interface
Hardware
* If any of these issues caused a schedule delay or need to be discussed further, include details in next slide.

4. Real Time Operating System
A variant of OS
Operates in constrained environment where computer memory and processing power is limited
Provides services in definite amount of time
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5. Features Fast Response times are highly predictable
Small and occupy very little memory
Consume fewer resources
Mission-critical
Unpredictable environment
Life risking applications

6. Examples of RTOS

7. Types of RTOS Hard Real-Time Systems Soft Real-Time Systems
It is based on the requirement of meeting the deadline within the time not the length of deadline.

8. Hard Real-Time Systems
Meets deadlines with zero degree of flexibility
Missed deadlines cause catastrophe
Cost of catastrophe is high

9. Example of Hard Real-Time Systems
Weapons defense system
Missile guidance system

10. Soft Real-Time Systems
Meets deadlines with some degree of flexibility
Missed deadline does not cause catastrophe
Costs rise in proportion to the delay

11. Example of Soft Real-Time Systems
DVD or multimedia players

12. Scheduling Make sure that all tasks meet their timing constraints
It is not a task but a function call [schedule()]
Called at various scheduling points likewise end of ISR, when tasks go to sleep or when they are ready to run
Types of algorithms
Preemptive priority based scheduling algorithm
Round Robin scheduling algorithm

13. Preemptive priority based scheduling algorithm
Each task has a priority and highest-priority task runs first

14. Round Robin scheduling algorithm
Each task of same priority uses time slice to achieve equal share of CPU execution time

15. Tasks An independent thread of execution It is schedulable
Characterized by associated name, unique ID, priority, task control block (TCB), stack & task routine
Each task moves from one state to another using finite state machine (FSM)

17. Semaphores
A kernel object that one or more threads of execution can acquire or release for the purposes of synchronization or mutual exclusion.
Acts like a key
Allows a task to carry out some operation or to access a resource
Types
Binary Semaphore
Counting Semaphore
Mutual Exclusion Semaphore

18. Message Queues
It is like a pipeline through which tasks & ISRs communicate and synchronize with data.

19. Ways to use Message Queues
Non-interlinked
one-way data communication
Interlocked
two-way data communication
Broadcast Communication

20. Exceptions & Interrupts
Exception is any event that disrupts the normal execution of the processor and forces the processor into execution of special instructions
Types
Synchronous Exceptions Raised by internal events like processor instructions
“An arithmetic operation that results in a division by zero”
Asynchronous Exceptions Associated with hardware signals from external hardware devices
Also called as INTERRUPTS
“Pushing the reset button on the embedded board”

21. Timers & Timer Services
It is the scheduling of an event according to a predefined time value in the future.
Similar to setting an alarm clock.
Types
Soft Timer Software events that are scheduled through a software facility
Hard Timer Physical timer chips that directly interrupt the processor when they expire

22. I/O Subsystem
Hides the device-specific information from the kernel as well as from the application developer and to provide a uniform access method to the peripheral I/O devices of the system.
Defines the standard set of functions called API.

23. Memory Management
Dynamic Memory allocation

24. Synchronization Resource Synchronization Activity Synchronization
Determines whether access to a shared resource is safe and, if not, when it will be safe.
Works on client-server model.
For instance, one task receives data from sensor & writes it to shared memory, a second task periodically receives data from shared memory and send it to display
Determine whether the execution of a multithreaded program has reached a certain state and if it hasn’t, when this state will be reached.
Can be either synchronous or asynchronous.
For instance, a complex computation can be divided among multiple tasks, some are I/O bound, some are CPU intensive and others are mainly floating point that rely on floating point coprocessors.

25. Communication Transfer of data from one task to another task.
Signal the occurrences of events from one task to another task
Control the execution of tasks by other task
Synchronize activities
Implement additional synchronization protocols for resource sharing

26. RTOS Distributions
QNX
RTLinux
VxWorks
Windows CE
OSE
freeRTOS

27. Thank You
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