Verification of an audio control protocol within real time process algebra

1. ABSTRACT In this paper, we formally analyze an audio control protocol developed by Philips. We use real time process algebra to model the protocol and weak bisimulation to verify its implementation against its specification. 1.1 Keywords Communication protoco1, real time system formal methods, process algebra, weak bisimulation. 2. INTRODUCTION In [4], Bosscher, Polak and Vaandrager have formally analyzed, based on weak timed forward simulation by using the timed I/O automata, a simple version of an audio control protocol developed by Philips for the physical layer of an interface bus that connects the various devices of some stereo equipment. The protocol, which uses Manchester encoding, has to deal with a significant uncertainty in the timing events due to both hardware and software constraints. It is a very nice example and therefore it has been suggested as a benchmark for other researchers to test their methods on, just as the Cizt and Mouse example of [lo] and the Gas Burner example of [ 143. Process algebra such as CCS [ll], CSP [9] and ACP [3] have been used to describe and analyze concurrently executing systems including communication protocols. The notion of weak bisimulation provides simple and elegant proof techniques for showing an implementation (usually a parallel process) meets its specification (usually a Permission IO make di&l/hard copy of all or pan of this work for personal or classroom use is gaated without fee provided that copies ate not made of dishibuted for profit or commerci al advantage, the copyright notice, tbe tide of the publication aad its date appear, aad notice is given that copying is by permission of ACM, Inc. To copy otherwise, to republish. to post oa servets or to redistribute to lists, requires prior SpeGifiC permission sad/or a fee. sequential process). There are many applications of process algebra for the formal verification of concurrent systems based on weak bisimulation [7,12,13] Recently there are many proposals and resultson real time process algebra. Most of the published .results regard completeness, de&lability and expressiveness issues. Unlike the untimed case, the timed version of weak bisimulation bears criticism of being too fine to be useful in formal verification of real time systems. So far there are very few published results in verification of real time systems (even toy examples) based on timed weak bisimulation. In this paper, we will present a formal analysis of the Philips's audio control protocol based on timed …