1. CONCEPTS OF REAL-TIME OPERATING SYSTEM

2. OBJECTIVE  To Understand Why we need OS?  To identify Types of OS  To Define Real - Time Systems  To Classify real time Systems  To Understand What is an RTOS ?  Components of RTOS  How to choose RTOS?  To know secrets of What makes an OS as an RTOS ?

3. OPERATING SYSTEMS - Converts hardware of the system into virtual machine. - Controls and coordinates use of hardware among various application programs among users. - Acts as an interface between users and hardware of the system.

4. Types of OS OS Size Function Multi-Programming Ex:Unix,WinNT Multi-Tasking Ex:RTX-51 Smaller Ex:RTX-51 Larger EX:WinNT,Unix

5. CPU I/O Devices I/O Sub System File Manager Language Support Utilities Application Programs Kernel Architecture For Larger OS Scheduler Despat -cher Int. handler

6. Dispatcher Scheduler Int. Handler. CPU I/O Devices Application Programs Kernel Architecture For Smaller OS

7. 3) Multi-tasking OS: - An instance of program in execution is called “Process / Task”. - Capability of OS to perform more than one task at same time. - Ability of OS to support concurrent execution of two (or) more programs. - OS switches from task to task simultaneously. - Two types are: 1) Cooperative 2) Preemptive 3) Multi-tasking OS: - An instance of program in execution is called “Process / Task”. - Capability of OS to perform more than one task at same time. - Ability of OS to support concurrent execution of two (or) more programs. - OS switches from task to task simultaneously. - Two types are: 1) Cooperative 2) Preemptive

8. 3) Multi-Programming OS: = Multi-Tasking + * Forms of memory protection * Enforces concurrency control when processes access shared I/O devices and files.

9. Definition of Real-Time Systems - Any system in which time at which output is produced is significant.This is because input corresponds to some movement in physical world and output has to relate to that same movement.The lag from input time to output time must be sufficiently small for acceptable timeliness. OR

10. - Systems in which correct responses are produced within a definite time limit. If computer responses exceed these time boundary then performance degradation and/or malfunction results. - Ex: Flight control, Industrial control, military applications, robotics, nuclear power plant control, automobile engine control, etc.

11. Real-Time Systems Hard Soft Classification of Real-Time Systems

12. Soft: - Acceptance of lower performance for lateness. - Rising cost for lateness of system. - Ex: vending machine, Temperature controller Hard: - No lateness is accepted under any circumstances. - Catastrophic failure if deadline missed - Cost of missing deadline is infinitely high - Ex: Missile system, aircraft.

13. What is RTOS? operating system, that helps to build real- time system.

14. Components of RTOS * Task Management * Memory Management * Intertask Communication * Intertask Synchronization

15. Functions of RTOS 1) Task Management: * Allocation of memory and CPU time to task. a) Scheduler: - To keep a record of the state of each task - To schedule the allocation of CPU time to each task. b) Dispatcher: - To perform the context-switching.

16. Task State Diagram NewReadyRunningHalted Waiting

17. CPU Scheduling - Deals with the problem of deciding which of the process(Task) in the ready queue is to be allocated with CPU. - Intention is to a) To maximize CPU utilization among different tasks in a multi-tasking program. b) To minimize waiting time.

18. Scheduling Algorithms a) First-Come-First-Served (FCFS) b) Shortest Job First (SJF) c) Priority based Pre-emption d) Round-Robin (RR)

19. 2) Memory management: - Dynamic memory Allocation - Used for storing intermediate results - Memory allocation and deallocation must exist within constant time limits. 3) Intertask Communication: various mechanism available are: (a) Pipes (b) Message queues (c) Remote procedural calls (RPC )

20. (a) Pipes: - Simple communication channel that can be used to send data from one task to another. - Pipe can be opened,closed,written to and read just like files. - Perform operation in only one direction. (b) RPC: - Procedure in one process can directly call procedure in another process. - Two process may be running on same computer or on 2 different computers connected by network.

21. (c) Message Queues: - It allows transmission of messages from one task to another task. 4 ) Intertask Synchronization: Classified as: (a) Signals (b) Semaphores (a) Signals: - Used when task synchronization is required without data exchange. - Simplest and fastest method.

22. (b) Semaphore: - Resources can be shared free of conflicts between the individual tasks. - Consists of a data item and a pair of operations, wait and release.

23. What makes an OS as RTOS? * An RTOS has to be multi-tasking and preemptible. * The notion of task priority has to exist. * The OS has to support task synchronization mechanisms. * A system of priority inheritance has to exist. * System should be deterministic.

25. Case Study - Why Windows NT is not an RTOS? * An RTOS has to be multi-tasking and preemptible. * The notion of task priority has to exist. - But has only few level of priority, therefore the predictability is poor * The OS has to support task synchronization mechanisms. * A system of priority inheritance has to exist.

26. * System should be deterministic.

28. How to Choose RTOS? Factors to be considered * Support of your processor of choice * Portability to new processor * Scalability to match varied application requirement * Multi processor support * Extended services such as Network support

29. * Standards / POSIX compliance * Language support * Development environment * Licensing arrangements & Price