SAM2000

SAM2000

• Introduction

• An Analyzable execution model

• Real-Time Analysis.

• Redesign the system

• Conclusions and Future Work

SAM2000

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

SAM2000

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.

SAM2000

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.

SAM2000

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

SAM2000

EXECUTION MODEL

)(Pr: NSignalsStatesocesssig

Signalsocesssreceived Pr:

otherwisePpri

ePsigpsifpPprimaxPpri

)(

),(),(),(:)(

)(),(),(::)( PreceivedandsePsigpspmaxPpri

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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.

A B C D E

5 4 1 3 8

2

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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

},{ rtcshababab BBmaxIcR

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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

SAM2000

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.