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lsli17 - 17-1 Scheduling 17-1 Goal: assign priorities so...

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17-1 17-1 Scheduling Goal: assign priorities so that deadlines met. Outline: Rate monotonic priority assignment. Hand priority assignment. Static scheduling for a cyclic executive. Source Burns & Wellings, “Real-Time Systems and Programming Languages,” second edition. New York: Addison-Wesley, 1997, chapter 13, pp. 399–440. 17-1 EE 4770 Lecture Transparency. Formatted 9:40, 14 April 1999 from lsli17. 17-1
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17-2 17-2 Definitions Scheduling is said to be effective if it guarantees deadlines will be met. A system is called pure periodic if all events are periodic all events’ deadlines are equal to their period worst-case execution times are available for all event handlers. A distinct priority assignment is one in which no two events have same priority. 17-2 EE 4770 Lecture Transparency. Formatted 9:40, 14 April 1999 from lsli17. 17-2
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17-3 17-3 Rate Monotonic Priority Assignment (RMPA) Method for assigning priorities with goal of meeting deadlines. Rate monotonic priority assignment does not guarantee deadlines will be met. A pure periodic system has a rate monotonic priority assignment when each event triggers an interrupt at a distinct strong priority level priority order is the same as frequency order (highest priority has shortest period, etc.). 17-3 EE 4770 Lecture Transparency. Formatted 9:40, 14 April 1999 from lsli17. 17-3
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17-4 17-4 Rate Monotonic Priority Assignment Example Assign priorities using RMPA for the pure-periodic events described in the table be- low: Event Handler Event Name Run Time Period A5 μ s3 0 μ s B4 μ s2 2 μ s C3 0 μ s 100 μ s Rate Monotonic Priority Assignment: Event Handler Event Strong Name Run Time Period Priority μ 0 μ μ 2 μ 0 μ s 100 μ s1 17-4 EE 4770 Lecture Transparency. Formatted 9:40, 14 April 1999 from lsli17. 17-4
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17-5 17-5 Effectiveness of Rate Monotonic Priority Assignment RMPA is not effective on all pure periodic systems. Two results useful for determining effectiveness: RMPA is effective iff there exists an effective distinct strong-priority assignment. That is, if RMPA is not effective ... then neither is any other assignment of distinct strong priorities. 17-5 EE 4770 Lecture Transparency. Formatted 9:40, 14 April 1999 from lsli17. 17-5
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17-6 17-6 Safe-Load Test: RMPA is effective if the following relation holds: X e ∈E t h ( e ) t b ( e ) < |E| ± 2 1 |E| - 1 ² , where E is the set of event names ( e.g. , E = { A, B, C } ), is the number of events ( e.g. , | E | = 3, called N in class), t h ( e ) is the handler run time for event e , and t b ( e ) is the period of event e .
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This note was uploaded on 12/11/2011 for the course EE 4770 taught by Professor Staff during the Fall '99 term at LSU.

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lsli17 - 17-1 Scheduling 17-1 Goal: assign priorities so...

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