REAL TIME COMPUTING: A NEW DISCIPLINE OF COMPUTER SCIENCE AND ENGINEERING

By Rezhin NwreeBayar Shahab

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OUTLINE֍ What is RT computing?

֍ Types of tasks

֍ Classifications of RT systems

֍ what is predictability ?

֍ Scheduling

֍Scheduling algorithms

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WHAT IS RT COMPUTING?

▪ Components of RT Computing

Very precise timing

High degree of reliability

The environment of operation

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TYPES OF TASKS

▪ Periodic tasks▪ Time-critical tasks ▪ Regular intervals

▪ Aperiodic tasks▪ Event based tasks

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CLASSIFICATIONS OF RT SYSTEMSBased on their deadlines tasks care classified as:

Hard RTMeet required deadlines within the bounded time otherwise it may lead tocatastrophic error (periodic tasks)

Firm RTMissing a deadline may not cause a catastrophic or fatal error, but may cause undesired effects or may degrade the performance of the system(aperiodic tasks)

Soft RTMissing a deadline may not be catastrophic and cause fatal errors, but they areundesired and unwanted(Best effort).

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WHAT IS PREDICTABILITY ▪ Demonstrate at design time that constraints of all tasks can

be met with 100% certainty (periodic hard deadline tasks )

▪ Constraints could be:▪ Time▪ Resource▪ Precedence ▪ Performance ▪ Environment

▪ Task characteristics i.e. # of tasks, their execution time

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PREDICTABILITY CONT. ▪ Probabilistic guarantee▪ A given task has a certain probability of

meeting its constraints▪ Run-time deterministic guarantee ▪ At run-time the system determine if the task’s constraints

can be met or not. (Dynamically arriving aperiodic tasks)

▪ Specification violation

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SCHEDULING ▪ Process of Determining when and where each task will be executed

▪ Schedulability study(feasibility)

Scheduling Infeasible schedule

feasible schedule

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SCHEDULING ALGORITHMS

▪RT applications can have different scheduling algorithms depending on several cases:

▪ Periodic or Aperiodic tasks

▪ Peermptible and Non-peermptible tasks

▪ Uniprocessor and Multiprocessor

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SCHEDULING ALGORITHMS

▪ Uniprocessor systems ▪ Static priority algorithm(RM)- Optimal among static

▪ Dynamic priority algorithm(EDF) – Optimal among both

▪ Multiple processor systems ▪ Static algorithm (List scheduling)

▪ Dynamic algorithm

▪ Centralized – central processor distributed to other processor

▪ Distributed – Tasks are scheduled by each processor autonomously