Formal verification for distributed real-time control: periodic Producer/Consumer

Abstract

The Producer/Comumer (P/C) has been used to model communication in networks. The modei states that in a q s e m there is a producer of a given informution and one or more consumers o f this information With this model dzflerenf kinds of communication failures may occuz In this paper; with the help ofthe adapted Jynchronous model (ASM), we show two methods for formally verifiing the n e c e s s q conditiom to avoid bufer overwrites in the P/C model. Spec@calIy, we aplore the constraints on communication parameters in distributed periodic control and more generally, we demonstrate how behavioral properties can be analyzed using formal methods. B INTRODUCTIQNFieldbusses are real-time Iocal area networks that have been designed to ensure communications at the process level. They are often used to transport input data &om a manufacturing process to controllers and output data back to the process. Designs must take into account the delays introduced by fieldbusses since these delays, and variation them, can deteriorate the quality and correctness of control. It is important to be able to study and verify the limitations on the upper and lower bounds of these time-varying delays to be able to guarantee a certain quality of control and predictable behavior. We shall focus on two types of delay -computation and communication delay -in a producer/consumer model (P/C) with periodic behavior. To this end, we will explore how to formally represent a periodic PIC based on the adapted synchronous model (ASM), a useful abstraction of the computation and communication tasks of periodic applications.More generally, we are interested in applying two different approaches of specification and verification of properties of distributed real-time control applications. Both approaches allow the synthesis of a formal representation which provides us with a nonambiguous description of the computation and communication aspects of applications with periodic behavior (e.g., applications such as control and command systems distributed over a fieldbus network). Both formal models extend the applicability ofthe synchronous model describing how distributed processors perfom computations in a synchronous manner (they perform in a lock-step fashion), and how the communication medium is synchronous (message delivery within a bounded delay).Organization. The paper will be organized as follows. After this introduction we present the synchronous model in nonformal terms, and the principal characteristics and parameters it defines for representing computation and communication.We also present some of the properties that applications corresponding to the informal model should have (ie. sufficient conditions on timing which guarantee that communication overwrites do not occur). The next two sections show how the informal description is formalized. In the first case we use the synchronous language ESTEFEL, and in the second case we use stockmfic timed petri nets. For both representations we discuss how to verify properties dealing with the timely sending a...

Reconfigurable Distributed Control

“…In this direction, Koppenhoefer and Decotignie (1996) have proposed a formal verification of distributed real-time control based on periodic producer/consumer.…”