Page 107 - DCAP608_REAL TIME SYSTEMS

Real Time Systems

Notes  A sporadic job that activates robotic arm is released when a defective part is detected.
 The arm, when activated, removes the part from the conveyor belt.
 The scheduler accepts the new job only if no sporadic jobs in system are adversely affected.
 The scheduler maintains a queue of accepted sporadic jobs in non-decreasing order of
their deadlines and inserts each newly accepted sporadic job into this queue in this order.
 Whenever a server or job completes the cyclic executive wakes up to execute.

10.4 Keywords

Acceptance Test: In acceptance test scheduler checks whether the newly released sporadic job can
be feasibly scheduled with all the jobs in the system at the time.
Aperiodic Tasks: It is the average fraction of processor time required by all the aperiodic tasks
in the system.
Cyclic EDF Algorithm: It is the only class of algorithms that perform acceptance tests at the
beginnings of frames.
Deadline First Algorithm: It is universal for sets of sporadic and periodic tasks and for sets of
concrete sporadic tasks.

EDF Algorithm: The EDF algorithm is a good way to schedule accepted sporadic jobs.
Sporadic Job: It is in the system is one that was accepted earlier but is not yet complete at the
time.

10.5 Review Questions

1. Define the term slack stealing.
2. How does slack stealing work with aperiodic jobs?
3. What is the average response time? Give some example.
4. Differentiate between average queuing time and total average utilization.
5. What is the acceptance test and explain their significance?

6. What is cyclic EDF algorithm?

Answers: Self Assessment

1. off-line 2. priori
3. Cyclically 4. Hardware
5. Minimal 6. More

7. False 8. True
9. True 10. True
11. True 12. True

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