An Analyzable execution model

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SAM2000

• Introduction
• An Analyzable execution model
• Real-Time Analysis.
• Redesign the system
• Conclusions and Future Work

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INTRODUCTION

• Real-Time embedded systems are spreading to more
  and more fields and their complexity and
  criticality have grown dramatically.
• The complexity of this kind of system comes from
  the non-functional requirements
• Safety
• Robustness
• Timeliness

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INTRODUCTION

• Most of these systems are controllers that have
  to respond in a limited period of time
• FDT is a promising way to deal with the
  increasing complexity of these systems.
• SDL presents difficulties to express real-time
  constraints and to prevent real-time anomalies.
• RMA provides a collection of quantitative methods
  to predict the timing behaviour of the systems.

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OUR PROPOSALS

• To integrate RMA in the design of real-time
  aplications using SDL.
• We provide a predictable execution model for SDL.
• We take advantage of SDL characteristics to get a
  more accurate analysis
• Precedence constraints
• SDL semantics
• Finally, we propose a set of techniques to
  redesign the system in order to meet the imposed
  deadlines.

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EXECUTION MODEL

• Priorities are assigned to transitions, not to
  processes
• Process priorities are dinamic, depending on
  their present states and the received signals.
• A transition can be preempted by another
  transition of higher priority, but belonging to
  another process

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EXECUTION MODEL
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REAL-TIME ANALYSIS

• The objective is to calculate the response time
  of the external events in the system.

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REAL-TIME ANALYSIS
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REAL-TIME ANALYSIS(2)

• To get more accurare results we take into account
  the following
• There exist precedence relations between the
  transitions that respond to an external event.
• SDL semantics.

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PRECEDENCE RELATIONS

• This characteristic helps us to reduce the number
  of transitions to take into account in the
  interference calculation.

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SDL SEMANTICS

• SDL semantics does not allow that two transitions
  that belong to the same SDL process execute
  concurrently.
• This fact, besides the precedence relations,
  reduces the number of transitions that can
  interrupt our transition.
• This characteristic introduces a new blocking
  source run to completion blocking.

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EXAMPLES
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EXAMPLES(2)
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EXAMPLES(3)

• Two possible sequences of transitions can
  interrupt transition t
• ti2, ti3 ti5
• If we take into account SDL semantics
• ti2 ti5
• ti3 cannot interrupt tab because the share the
  same SDL process
• This way we reduce the number of interrupting
  transitions but in other cases the blocking time
  can increase

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EXAMPLES(4)
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Response Time calculation

• Select the transition sequence with the worst
  interference time. Iab
• Calculate the maximum blocking time between
• Blocking due to acess to shared resources. Bsh
• Run to Completion Blocking Brtc

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Redesign

• Rate monotonic analysis allows us to organize
  processes and resources.
• The calculation of response times helps us to
  redesign SDL specifications to meet the
  deadlines.
• Four possible techniques
• Transition period analysis.
• Task Transference.
• Intermediate transition elimination.
• Process Creation

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Task Transference

• Objective Reassign tasks of transitions to
  transitions with higher priority.
• Look for consecutive transitions that respond to
  the events that do not meet the deadlines with an
  increase or decrease of priority.
• Take the tasks from lower priority transitions to
  the higher priority.
• It is possible that other events increase the
  response time, but it is not negative if all the
  events meet the deadlines.
• SDL processes cannot access to variables of other
  processes. The solution is to use passive process
  to share variables with access by means of RPC.

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Task transference
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Intermediate transition elimination

• Objective It eliminates transitions in the
  system but maintaining the system responsiveness.

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Creating SDL processes

• The objective To increase the concurrency in the
  system

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Creating SDL processes
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Conclusions and future work

• We have proposed to integrate RMA in SDL
  specifications.
• We have introduced a set of techniques to
  redesign the system in order to meet the imposed
  deadlines.
• Future work
• To apply RMA and redesign strategies to UML.
• To develop tools and the interfaces to integrate
  these proposals in commercial tools.