lecture03-handout4 - Safe State Machines vs. Esterel...

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Unformatted text preview: Safe State Machines vs. Esterel Homework 01—Due: 21 April 2005 Modeling/Distributed RT Systems—Lecture 03 Prof. Dr. Reinhard von Hanxleden Christian-Albrechts Universit¨ at Kiel Department of Computer Science and Applied Mathematics Real-Time Systems and Embedded Systems Group 14 April 2005 Last compiled: 14th April 2005, 18:53 hrs Statecharts II WS 2004/05 Modeling/Distributed RT Systems—Lecture 03 Slide 1 Safe State Machines vs. Esterel Homework 01—Due: 21 April 2005 Overview Safe State Machines vs. Esterel Signals and Synchrony The ABRO Example Write Things Once The multiform notion of time Uses, Advantages, Disadvantages Homework 01—Due: 21 April 2005 WS 2004/05 Modeling/Distributed RT Systems—Lecture 03 Slide 2 Safe State Machines vs. Esterel Homework 01—Due: 21 April 2005 Signals and Synchrony The ABRO Example Write Things Once The multiform notion of time Uses, Advantages, Disadvantages Introduction to Esterel Imperative, textual language Concurrent Based on synchronous model of time Program execution synchronized to an external clock Like synchronous digital logic Suits the cyclic executive approach Same model of computation as SyncCharts/Safe State Machines (SSMs) EsterelStudio generates Esterel from SSMs as intermediate code Thanks to Stephen Edwards ( http: // www1. cs. columbia. edu/ ~sedwards/ ) for providing part of the following material WS 2004/05 Modeling/Distributed RT Systems—Lecture 03 Slide 3 Safe State Machines vs. Esterel Homework 01—Due: 21 April 2005 Signals and Synchrony The ABRO Example Write Things Once The multiform notion of time Uses, Advantages, Disadvantages Introduction to Esterel Two types of statements: Those that take “zero time” (execute and terminate in same instant, e.g., emit ) Correspond to Connectors in SSMs Those that delay for a prescribed number of cycles (e.g., await ) Correspond to States in SSMs WS 2004/05 Modeling/Distributed RT Systems—Lecture 03 Slide 4 Safe State Machines vs. Esterel Homework 01—Due: 21 April 2005 Signals and Synchrony The ABRO Example Write Things Once The multiform notion of time Uses, Advantages, Disadvantages Signals Esterel programs/SSMs communicate through signals These are like wires Each signal is either present or absent in each cycle Can’t take multiple values within a cycle Presence/absence not held between cycles Broadcast across the program Any process can read or write a signal WS 2004/05 Modeling/Distributed RT Systems—Lecture 03 Slide 5 Safe State Machines vs. Esterel Homework 01—Due: 21 April 2005 Signals and Synchrony The ABRO Example Write Things Once The multiform notion of time Uses, Advantages, Disadvantages Signals Status of an input signal is determined by input event, and by local emissions Status of local or output signal is determined per instant Default status: absent Must execute an “ emit O ” statement to set signal present await A : Waits for A and terminates when A occurs WS 2004/05 Modeling/Distributed RT Systems—Lecture 03...
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lecture03-handout4 - Safe State Machines vs. Esterel...

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