Page 43 - DCAP608_REAL TIME SYSTEMS

Real Time Systems

Notes  If deadline is infinity, then job has no deadline.
 Absolute deadline is equal to release time plus relative deadline.
 Timing constraint is a constraint imposed on timing behaviour of a job: hard or soft.
 Hard real-time systems have very strict time constraints, in which missing the specified
deadline is unacceptable.
 Soft real-time systems also have time constraints; however, missing some deadline may
not lead to catastrophic failure of the system.

3.7 Keywords

Computations: Computations are non-binary time constraints, even when a large merit penalty
is incurred for completing it after a deadline.
Hard Real-time System: It is the system which guarantees that critical tasks complete on time
and this goal requires that all delays in the system be bounded from the retrieval of the stored
data to the time that it takes the operating system to finish any request made of it.
Job: This is a unit of work that is scheduled and executed by a system and executed by the
operating system on a processor and may depend on some resources.

Processor (P): It is an active object on which job executes. It has a speed attribute which determines
the rate of progress a job makes toward completion.
Release Time: It is the time of job, or is the instant of time at which the job becomes available for
execution.
Soft Real-time System: It is a system where a critical real-time task gets priority over other tasks
and retains that priority until it completes.
Timing Constraints: These are the factors/parameters on which the correctness of real-time
tasks depends.
3.8 Review Questions

1. Define the term the job in general.
2. Explain the concept of job and processors in real-time system.
3. Define release time.
4. How many algorithms used to find the release time?

5. Explain ITR algorithm in detail.
6. Algorithm ITR terminates after a finite number of iterations. Comment on it.
7. Define the terms deadline and timing constraints.

8. Discuss different types of timing constraints.
9. Differentiate between soft and hard timing constraints.
10. What is the basic component of any real-time application?

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