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

SAM2000 REAL-TIME ANALYSIS The objective is to calculate the response time of the external events in the system.

SAM2000 REAL-TIME ANALYSIS

SAM2000 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.

SAM2000 PRECEDENCE RELATIONS This characteristic helps us to reduce the number of transitions to take into account in the interference calculation.

SAM2000 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.

SAM2000 EXAMPLES

SAM2000 EXAMPLES(2)

SAM2000 EXAMPLES(3) Two possible sequences of transitions can interrupt transition t: {t i2, t i3 } {t i5 } If we take into account SDL semantics: {t i2 } {t i5 } t i3 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

SAM2000 EXAMPLES(4)

SAM2000 Response Time calculation Select the transition sequence with the worst interference time. I ab Calculate the maximum blocking time between: –Blocking due to acess to shared resources. B sh –Run to Completion Blocking B rtc

SAM2000 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.

SAM2000 Task transference

SAM2000 Intermediate transition elimination Objective: It eliminates transitions in the system but maintaining the system responsiveness.

SAM2000 Creating SDL processes The objective: To increase the concurrency in the system

SAM2000 Creating SDL processes

SAM2000 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.