Team for Research in
Ubiquitous Secure Technology

Citation
Edward A. Lee. "Is Truly Real-Time Computing Becoming Unachievable?". Talk or presentation, 3, April, 2007.

Abstract
Discrete-event (DE) models are formal system specifications that have analyzable deterministic behaviors. Using a global, consistent notion of time, DE components communicate via time-stamped events. DE models have primarily been used in performance modeling and simulation, where time stamps are a modeling property bearing no relationship to real time during execution of the model. In this paper, we extend DE models with the capability of relating certain events to physical time. We propose a programming model, called PTIDES (Programming Temporally Integrated Distributed Embedded Systems), which has DE semantics, but with carefully chosen relations between model time and real time. Key to making this model effective is to ensure that constraints that guarantee determinacy in the semantics are preserved at runtime. To accomplish this, we give a distributed execution strategy that obeys DE semantics without the penalty of totally ordered executions based on time stamps. Our technique relies on having a distributed common notion of time, known to some precision. Based on causality analysis of DE models, we define relevant dependency and relevant orders to enable out-of-order execution without compromising determinism and without requiring backtracking.

Electronic downloads

• RealTimeComputing_RTAS_Lee.pdf · application/pdf · 2042 kbytes
• RealTimeComputing_RTAS_Lee.ppt · application/vnd.ms-powerpoint · 2970 kbytes

• HTML

  Edward A. Lee. <a
  href="http://www.truststc.org/pubs/251.html"
  ><i>Is Truly Real-Time Computing Becoming
  Unachievable?</i></a>, Talk or presentation,  3,
  April, 2007.

• Plain text

  Edward A. Lee. "Is Truly Real-Time Computing Becoming
  Unachievable?". Talk or presentation,  3, April, 2007.

• BibTeX

  @presentation{Lee07_IsTrulyRealTimeComputingBecomingUnachievable,
      author = {Edward A. Lee},
      title = {Is Truly Real-Time Computing Becoming Unachievable?},
      day = {3},
      month = {April},
      year = {2007},
      abstract = {Discrete-event (DE) models are formal system
                specifications that have analyzable deterministic
                behaviors. Using a global, consistent notion of
                time, DE components communicate via time-stamped
                events. DE models have primarily been used in
                performance modeling and simulation, where time
                stamps are a modeling property bearing no
                relationship to real time during execution of the
                model. In this paper, we extend DE models with the
                capability of relating certain events to physical
                time. We propose a programming model, called
                PTIDES (Programming Temporally Integrated
                Distributed Embedded Systems), which has DE
                semantics, but with carefully chosen relations
                between model time and real time. Key to making
                this model effective is to ensure that constraints
                that guarantee determinacy in the semantics are
                preserved at runtime. To accomplish this, we give
                a distributed execution strategy that obeys DE
                semantics without the penalty of totally ordered
                executions based on time stamps. Our technique
                relies on having a distributed common notion of
                time, known to some precision. Based on causality
                analysis of DE models, we define relevant
                dependency and relevant orders to enable
                out-of-order execution without compromising
                determinism and without requiring backtracking.},
      URL = {http://www.truststc.org/pubs/251.html}
  }
  

Posted by Mary Stewart on 13 Apr 2007.
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