NET 424: REAL-TIME SYSTEMS (Practical Part) Networks and Communication Department Tutorial 6 : on lecture 5

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 0.8 . Find a feasible schedule. 2) Suppose that the server is Deferrable server repeat the part 1. Networks and Communication Department

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. Networks and Communication Department

1. Answer (Cont.) Response time for the aperiodic job= 6.3-2.3=4 0.8 Networks and Communication Department

2. Answer Unlike a poller, however, when a deferrable server finds no aperiodic job ready for execution, it preserves its budget. Networks and Communication Department

2. Answer Tdf(2,0.5) Response time= 4.8-2.3=2.5 T1(3,1) T2(4, 0.5) Budget=1.5-0.8=0.7 Budget=1 Budget=0.5 Tdf(2,0.5) T1(3,1) T2(4, 0.5) T3(5,0.5) 0 1 2 3 4 5 6 7 Response time= 4.8-2.3=2.5 4.8 Networks and Communication Department

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