1. NET 424: REAL-TIME SYSTEMS (Practical Part)
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Tutorial 6 : on lecture 5

2. Question 1 Real Time System by Jane W. S. Liu Chapter 7.2 Solution
Q.7.2: A system contains three periodic tasks. They are (3,1), (4,0.5), (5,0.5).
The task system also contains a polling server whose period is 2 and budget =0.5. The polling server is scheduled with the periodic tasks rate-monotonically.
1)Suppose that an aperiodic task A arrives at 2.3 and has execution time Find a feasible schedule.
2) Suppose that the server is Deferrable server repeat the part 1.
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3. Answer
Sol:  in the rate-monotonically the priority is for the task who has the smallest period.
The aperiodic job has Release time = 2.3 and execution time =2.8.
The polling server acts as periodic tasks and hold the aperiodic job in a queue.
Polling server has period time=2; and the budget first = execution time = 0.5. It has it’s value (0.5) in the multiple of period 2, 4, 6, 8, . Otherwise, the budget is =0 which means it cannot handle apiriodic job.
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4. 1. Answer (Cont.) Response time for the aperiodic job= 6.3-2.3=4 0.8
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5. 2. Answer
Unlike a poller, however, when a deferrable server finds no aperiodic job ready for execution, it preserves its budget.
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6. 2. Answer Tdf(2,0.5) Response time= 4.8-2.3=2.5 T1(3,1) T2(4, 0.5)
Budget= =0.7
Budget=1
Budget=0.5
Tdf(2,0.5)
T1(3,1)
T2(4, 0.5)
T3(5,0.5)
Response time= =2.5
4.8
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7. The End
Any Questions ?
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