Roberto Passerone

Automatic synthesis of interfaces between incompatible protocols

At the system level, reusable Intellectual Property (or IP) blocks can be represented abstractly as blocks that exchange messages. The concrete implementations of these IP blocks must exchange the messages through complex signaling protocols. Interfacing between IP that use different signaling protocols is a tedious and error prone design task. We propose using regular expression based protocol descriptions to show how to map the message onto a signaling protocol. Given two protocols, an algorithm is proposed to build an interface machine. We have implemented our algorithm in a program named PIG that synthesizes a Verilog implementation based on a regular expression protocol description.

A Platform-Based Taxonomy for ESL Design

This article presents a taxonomy for ESL tools and methodologies that combines UC Berkeleys platform-based design terminologies with Dan Gajskis Y-chart work. This is timely and necessary because in the ESL world we seem to be building tools without first establishing an appropriate design flow or methodology, thereby creating a lot of confusion. This taxonomy can help stem the tide of confusion

Taming Dr. Frankenstein: Contract-Based Design for Cyber-Physical Systems

Cyber-physical systems combine a cyber side (computing and networking) with a physical side (mechanical, electrical, and chemical processes). In many cases, the cyber component controls the physical side using sensors and actuators that observe the physical system and actuate the controls. Such systems present the biggest challenges as well as the biggest opportunities in several large industries, including electronics, energy, automotive, defense and aerospace, telecommunications, instrumentation, industrial automation. Engineers today do successfully design cyber-physical systems in a variety of industries. Unfortunately, the development of systems is costly, and development schedules are difficult to stick to. The complexity of cyber-physical systems, and particularly the increased performance that is offered from interconnecting what in the past have been separate systems, increases the design and verification challenges. As the complexity of these systems increases, our inability to rigorously model the interactions between the physical and the cyber sides creates serious vulnerabilities. Systems become unsafe, with disastrous inexplicable failures that could not have been predicted. Distributed control of multi-scale complex systems is largely an unsolved problem. A common view that is emerging in research programs in Europe and the US is “enabling contract-based design (CBD),” which formulates a broad and aggressive scope to address urgent needs in the systems industry. We present a design methodology and a few examples in controller design whereby contract-based design can be merged with platform-based design to formulate the design process as a meet-in-the-middle approach, where design requirements are implemented in a subsequent refinement process using as much as possible elements from a library of available components. Contracts are formalizations of the conditions for correctness of element integration (horizontal contracts), for lower level of abstraction to be consistent with the higher ones, and for abstractions of available components to be faithful representations of the actual parts (vertical contracts).

Languages and tools for hybrid systems design

The explosive growth of embedded electronics is bringing information and control systems of increasing complexity to every aspects of our lives. The most challenging designs are safety-critical systems, such as transportation systems (e.g., airplanes, cars, and trains), industrial plants and health care monitoring. The difficulties reside in accommodating constraints both on functionality and implementation. The correct behavior must be guaranteed under diverse states of the environment and potential failures; implementation has to meet cost, size, and power consumption requirements. The design is therefore subject to extensive mathematical analysis and simulation. However, traditional models of information systems do not interface well to the continuous evolving nature of the environment in which these devices operate. Thus, in practice, different mathematical representations have to be mixed to analyze the overall behavior of the system. Hybrid systems are a particular class of mixed models that focus on the combination of discrete and continuous subsystems. There is a wealth of tools and languages that have been proposed over the years to handle hybrid systems. However, each tool makes different assumptions on the environment, resulting in somewhat different notions of hybrid system. This makes it difficult to share information among tools. Thus, the community cannot maximally leverage the substantial amount of work that has been directed to this important topic. In this paper, we review and compare hybrid system tools by highlighting their differences in terms of their underlying semantics, expressive power and mathematical mechanisms. We conclude our review with a comparative summary, which suggests the need for a unifying approach to hybrid systems design. As a step in this direction, we make the case for a semantic-aware interchange format, which would enable the use of joint techniques, make a formal comparison between different approaches possible, and facilitate exporting and importing design representations.

Convertibility verification and converter synthesis: two faces of the same coin

An essential problem in component-based design is how to compose components designed in isolation. Several approaches have been proposed for specifying component interfaces that capture behavioral aspects such as interaction protocols, and for verifying interface compatibility. Likewise, several approaches have been developed for synthesizing converters between incompatible protocols. In this paper, we introduce the notion of adaptability as the property that two interfaces have when they can be made compatible by communicating through a converter that meets specified requirements. We show that verifying adaptability and synthesizing an appropriate converter are two faces of the same coin: adaptability can be formalized and solved using a game-theoretic framework, and then the converter can be synthesized as a strategy that always wins the game. Finally we show that this framework can be related to the rectification problem in trace theory.

A Modal Interface Theory for Component-based Design

This paper presents the modal interface theory, a unification of interface automata and modal specifications, two radically dissimilar models for interface theories. Interface automata is a game-based model, which allows the designer to express assumptions on the environment and which uses an optimistic view of composition: two components can be composed if there is an environment where they can work together. Modal specifications are a language theoretic account of a fragment of the modal mu-calculus logic with a rich composition algebra which meets certain methodological requirements but which does not allow the environment and the component to be distinguished. The present paper contributes a more thorough unification of the two theories by correcting a first attempt in this direction by Larsen et al., drawing a complete picture of the modal interface algebra, and pushing the comparison between interface automata, modal automata and modal interfaces even further. The work reported here is based on earlier work presented in [41] and [42].

Modal interfaces: unifying interface automata and modal specifications

This paper presents a unification of interface automata and modal specifications, two radically dissimilar models for interface theories. Interface automata is a game-based model, which allows to make assumptions on the environment and propose an optimistic view for composition : two components can be composed if there is an environment where they can work together. Modal specification is a language theoretic account of a fragment of the modal mu-calculus logic that is more complete but which does not allow to distinguish between the environment and the component. Partial unifications of these two frameworks have been explored recently. A first attempt by Larsen et al. considers modal interfaces, an extension of modal specifications that deals with compatibility issues in the composition operator. However, this composition operator is incorrect. A second attempt by Raclet et al. gives a different perspective, and emphasises on conjunction and residuation of modal specifications, including when interfaces have dissimilar alphabets, but disregards interface compatibility. The present paper contributes a thorougher unification of the two theories by correcting the modal interface composition operator presented in the paper by Larsen et al., drawing a complete picture of the modal interface algebra, and pushing even further the comparison between interface automata, modal automata and modal interfaces.

System level design paradigms: Platform-based design and communication synthesis

Embedded system level design must be based on paradigms that make formal foundations and unification a cornerstone of their construction. Platform-Based designs and communication synthesis are important components of the paradigm shift we advocate.Communication synthesis is a fundamental productivity tool in a design methodology where reuse is enforced. Communication design in a reuse methodology starts with a set of functional requirements and constraints on the interaction among components and then proceeds to build protocols, topology, and physical implementations that satisfy requirements and constraints while optimizing appropriate measures of efficiency of the implementation. Maximum efficiency can be reached when the communication specifications are entered at high levels of abstraction and the design process optimizes the implementation from this specification. Unfortunately, this process is very difficult if it is not cast in a rigorous framework. Platform-Based design helps define a successive refinement process where each step can be carried out automatically and optimized appropriately. We present two cases, an on-chip and a wireless sensor network design, where the resulting methodology gave encouraging results.

metro II: A design environment for cyber-physical systems

Cyber-Physical Systems are integrations of computation and physical processes and as such, will be increasingly relevant to industry and people. The complexity of designing CPS resides in their heterogeneity. Heterogeneity manifest itself in modeling their functionality as well as in the implementation platforms that include a multiplicity of components such as microprocessors, signal processors, peripherals, memories, sensors and actuators often integrated on a single chip or on a small package such as a multi-chip module. We need a methodology, tools and environments where heterogeneity can be dealt with at all levels of abstraction and where different tools can be integrated. We present here Platform-Based Design as the CPS methodology of choice and metroII, a design environment that supports it. We present the metamodeling approach followed in metroII, how to couple the functionality and implementation platforms of CPS, and the simulation technology that supports the analysis of CPS and of their implementation. We also present examples of use and the integration of metroII with another popular design environment developed at Verimag, BIP.

Overcoming heterophobia: modeling concurrency in heterogeneous systems

System level design is complex. One source of this complexity is that systems are often heterogeneous: different models of computation (e.g., dataflow, FSMs) are used to describe different components of a system. Existing formal methods for concurrent systems are typically based on one particular model of computation, so it is difficult to formalize the interaction between heterogeneous components. In this paper, we develop a framework for formalizing the relationships between different models of computation.