Olfa Mosbahi

Reconfigurable Coordination of Distributed Discrete Event Control Systems

Dynamic reconfigurability is receiving more and more attention from both academy and industry, which means the ability to flexibly modify system functions by adding/removing hardware/software components, modifying logic relation between components, or updating particular system data at runtime without sacrificing the system performance. A distributed reconfigurable discrete event control system (DRDECS) is composed of several networked reconfigurable subsystems. In order to realize system functions, these reconfigurable subsystems communicate and coordinate with each other, since any casually reconfiguration applied to a subsystem may cause risks to others, or even to the safety of the whole system. This brief proposes a new coordination method for a DRDECS, where each subsystem is modeled by a reconfigurable timed net condition/event system. A virtual coordinator together with a communication protocol between it and subsystems is developed in order to achieve two aims: 1) to coordinate subsystems with an optimal coordination solution using judgement matrices while multiple subsystems require global reconfigurations and 2) to reduce exchanged messages between the coordinator and these subsystems. Furthermore, for the purpose of checking functional and temporal properties of a DRDECS with this virtual coordinator, a computation tree logic-based model checking method is applied. Finally, a hypothetic manufacturing plant is used as a running example to illustrate this brief.

R-TNCES: A Novel Formalism for Reconfigurable Discrete Event Control Systems

This study deals with the formal modeling and verification of reconfigurable discrete event control systems (RDECSs). The behavior of an RDECS is represented by that of control components (CCs) and the communication among them. A new formalism, called Reconfigurable Timed Net Condition/Event Systems (TNCES) (R-TNCES), is proposed for the optimal functional and temporal specification of RDECS, which is defined by a behavior module and a control module. The former is a union of various superposed TNCESs, where TNCES-based CC modules are basic units. The latter is a set of reconfiguration functions dealing with the automatic transformations of these TNCESs in response to errors or user requirements by enabling or disabling CC modules, changing condition signals and/or event signals among them, and also treating the state feasibility before and after reconfigurations. To control the verification complexity of R-TNCES, a layer-by-layer verification method is developed, where the similarities of different TNCESs in the behavior module are considered. The contribution of this original paper is applied to a benchmark production system.

R-Node: New Pipelined Approach for an Effective Reconfigurable Wireless Sensor Node

The pipeline of reconfiguration is a novel approach that gives a decision making mechanism for any system of tasks when several reconfiguration scenarios are required. These scenarios represent the run-time operations that allow automatic functional modification of the system behavior. In the case of their frequent income, the pipeline follows a specific set of steps in order to figure out the scenarios that need to be applied without altering its own performance. The steps are represented by a sequence of modules. The first module checks the availability of the resources needed by the tasks. The second maintains the stability by rejecting any insupportable flow of software reconfigurations that can destabilize a system. The third module checks the availability of memory for each software reconfiguration request, whereas the fourth verifies the availability of energy for the execution of a new system software configuration. The last module checks the schedulability of this configuration by changing the priorities of the finally accepted tasks in order to reduce their response and blocking times, and to meet their deadlines. The feasibility of the reconfiguration through this approach allows its implementation in wireless sensor nodes. Known by their important requirements in terms of memory and energy, this proposition is adequate when it comes to guaranteeing a maximum lifespan of the nodes. Therefore, the pipeline of reconfiguration is integrated as a middleware within the software architecture of a node. The functionality of this middleware is coordinated by the mean of a set of threads that manage the communication between the pipeline of reconfiguration and the operating system. A tool has been developed within LISI Laboratory to encode this proposition and show its impact on a large range of real devices under diversified scenarios of reconfigurations.

BROMETH: Methodology to design safe reconfigurable medical robotic systems

This research paper deals with the development of a medical robotized control system for supracondylar humeral fracture treatment. Concurrent access to shared resources and applying reconfiguration scenarios can jeopardize the safety of the system.

A formal approach to check and schedule reconfigurable embedded control systems

This paper deals with the development of reconfigurable control systems following the component-based International Industrial Standard IEC61499. In this standard, a function block is an event-triggered component owning data and an application is a FB network that has to satisfy temporal properties. This network is totally changed or modified if a reconfiguration scenario is applied at run-time. We classify at first time all possible reconfiguration forms and we propose thereafter an Agent-based architecture to handle them. To verify temporal properties on the FB network corresponding to each reconfiguration scenario, we analyze the schedulability of the corresponding blocks. If it is feasible, then a static scheduling is generated as a sequencing to be used by the OS when the Agent applies at run-time the corresponding scenario. We deduce finally the whole system feasibility if the FB network corresponding to each possible scenario is feasible. A tool X - Reconfig is developed in our research laboratory to support the paper contribution.

GR-TNCES: New extensions of R-TNCES for modelling and verification of flexible systems under energy and memory constraints

This study deals with the formal modeling and verification of Adaptive Probabilistic Discrete Event Control Systems (APDECS). A new formalism called Generalized Reconfigurable Timed Net Condition Event Systems (GR-TNCES) is proposed for the optimal functional and temporal specification of APDECS. It is composed of behavior and control modules. This formalism is used for the modeling and control of unpredictable as well as predictable reconfiguration processes under memory and energy constraints. A formal case study is proposed to illustrate the necessity of this formalism and a formal verification based on the probabilistic model checker Prism.

A Specification and Validation Technique Based on STATEMATE and FNLOG

The paper presents a specification technique borrowing features from two classes of specification methods, formal and semi-formal ones. Each of the above methods have been proved to be useful in the development of real-time and critical systems and widely reported in different papers [1], [2]. Formal methods are based on mathematical notations and axiomatic which induce verification and validation. Semi-formal methods are, in the other hand, graphic, structural and user-friendly. Each method is applied on a suitable case study, that we regret some missing features we could found in the other class. This remark has motivated our work. We are interested in the integration of formal and semi-formal methods in order to lay out a specification approach which combines the advantages of theses two classes of methods. The proposed technique is based on the integration of the semi-formal method STATEMATE [3] and the temporal logic FNLOG [7]. This choice is justified by the fact that FNLOG is formal, deals with quantitative temporal properties and that these two approaches have a compatibility which simplifies their integration [7]. The proposed integration approach uses the notations of STATEMATE and FNLOG, defines a various transformations rules of a STATEMATE specification towards FNLOG and extends the axiomatic of the temporal logic FNLOG by new lemmas to deal with duration properties. The paper presents the various steps of our integration approach.

RA2DL: New flexible solution for adaptive AADL-based control components

The paper deals with adaptive component-based control systems following the Architecture Analysis and Design Language (denoted by AADL). A system is assumed to be a network of software and hardware AADL components that share the control of corresponding physical processes. A component is composed of a set of algorithms encoding the control after any reception of external events and data signals. The termination of execution is generally done with the emission of data and event signals to remote components. According to various evolutions in environment, the system is required to be dynamically reconfigured at run-time to adapt its control functions. We are interested in local reconfigurations ofr components dealing with the activation-deactivation-update of algorithms and/or data-event inputs and outputs. We propose RA2DL as a solution for reconfigurable AADL components, and define a hierarchical-based architecture to dynamically handle all possible reconfiguration scenarios at run-time. We model and verify this solution and develop a tool for its simulation by taking a real-case study as a running example.

Reconfigurable priority ceiling protocol under rate monotonic based real-time scheduling

This research paper deals with reconfigurable real-time systems to be adapted to their environment under user requirements. A reconfiguration scenario is a run-time software operation that allows the addition, removal and update of real-time OS tasks which can share resources and should meet corresponding deadlines. We propose a new Reconfigurable Priority Ceiling Protocol (denoted by RPCP) that avoids deadlocks after any reconfiguration scenario and changes the priorities of tasks in order to reduce their response and blocking times, and to meet their deadlines. This protocol requires the use of two virtual processors in order to guarantee the non-interruption of execution during the reconfiguration step. We develop a tool that encodes this protocol which is applied to a case study.

Specification Approach using GR-TNCES: Application to an Automotive Transport System.

The features of probabilistic adaptive systems are especially the uncertainty and reconfigurability. The structure of a part of the system may be totally unknown or partially unknown at a particular time. Openness is also an inherent property, as agents may join or leave the system throughout its lifetime. This poses severe challenges for state-based specification. The languages in which probabilistic reconfigurable systems are specified should be clear and intuitive, and thus accessible to generation, inspection and modification by humans. This paper introduces a new approach for specifying adaptive probabilistic discrete event systems. We introduce the semantics of GR-TNCES to optimize the specification of unpredictable timed reconfiguration scenario running under resources constraints. We also apply this approach to specify the requirements of an automotive transport system and we evaluate its benefits.