Analytic real-time analysis and timed automata

International Journal on Software Tools for Technology Transfer, 2012

Compositionality can be a helpful paradigm for coping with the complexity of large embedded systems with real-time constraints. This article exploits state-less assume/guarantee real-time interfaces extended by component properties, both to be satisfied invariantly by any component implementing the respective interface. This supports compositional evaluation of system designs, as overall properties of the latter can be derived from the component interfaces, rather than verifying them for the complete system model at analysis time. Moreover, our design strategy based on extended analytic real-time interfaces features an incremental, and component-wise development of (heterogeneous) system designs. This is, because the interface-derived properties of an overall system design are proven to be invariant under composition and substitution of interfaces and components, as long as the interface definitions are consistent, the (potentially heterogeneous) components implement their interfaces, and a dedicated inclusion criterion holds. This article develops the machinery for deriving analytic interface descriptions from Timed Automata-based component models. It develops the required consistency and conformance tests for deciding the aforementioned invariance of interfaces and components with respect to composition and substitution. This way we hope to advocate a strictly compositional design approach and improve the scalability of statebased analysis methods which we investigate in several case studies.

Proceedings. 2003 International Symposium on System-on-Chip (IEEE Cat. No.03EX748)

We describe the Timed Input/Output Automata (TIOA) framework, a general mathematical framework for modeling and analyzing real-time systems. It is based on timed I/O automata, which engage in both discrete transitions and continuous trajectories. The framework includes a notion of external behavior, and notions of composition and abstraction. We define safety and liveness properties for timed I/O automata, and a notion of receptiveness, and prove basic results about all of these notions. The TIOA framework is defined as a special case of the new Hybrid I/O Automata (HIOA) modeling framework for hybrid systems. Specifically, a TIOA is an HIOA with no external variables; thus, TIOAs communicate via shared discrete actions only, and do not interact continuously. This restriction is consistent with previous real-time system models, and gives rise to some simplifications in the theory (compared to HIOA). The resulting model is expressive enough to describe complex timing behavior, and to express the important ideas of previous timed automata frameworks.

Lecture Notes in Computer Science, 2010

We present a real-time specification framework based on Timed I/O Automata and a comprehensive tool support for it. The framework supports various design methodologies including: top-down refinement-for decomposition of abstract specifications towards increasingly detailed models; bottom-up abstraction-for synthesis of complex systems from more concrete models; and step-wise modularisation of requirements-to factor out behaviours given by existing available components from a complex global requirements specification to be implemented. These methodologies are realized by consecutive applications of operators from the following set: refinement, consistency checking, logical and structural composition and quotienting. Additionally, our tool allows combining the component-oriented design process with verification of temporal logic properties increasing the flexibility of the process.

Zenodo (CERN European Organization for Nuclear Research), 2008

Lecture Notes in Computer Science, 1998

To support top-down design of distributed real-time systems, a framework of mixed terms has been incorporated in the veri cation system PVS. Programs and assertional speci cations are treated in a uniform way. We focus on the timed behaviour of parallel composition and hiding, presenting several alternatives for the de nition of a denotational semantics. This forms the basis of compositional proof rules for parallel composition and hiding. The formalism is applied to an example of a hybrid system, which also serves to illustrate our ideas on platformindependent programming.

IEEE Transactions on Software Engineering, 1998

We propose a method for analyzing partially-implemented real-time systems. Here we consider real-time concurrent systems for which some components are implemented in Ada and some are partially specified using regular expressions and Graphical Interval Logic (GIL), a real-time temporal logic. We show how to construct models of the partially-implemented systems that account for such properties as run-time overhead and scheduling of processes, yet support tractable analysis of nontrivial programs. The approach can be fully automated, and we illustrate it by analyzing a small example.

Proceedings of the conference on Design, automation and test in Europe - DATE '00, 2000

Temporal logic model checking is a technique for the automatic verification of systems against specifications. Besides the correctness of safety and liveness properties it is often important to determine critical answer and delay times of systems, especially if they are embedded in a real-time environment. In this paper we present an approach which allows the verification as well as the timing analysis of realtime systems. The systems are described as networks of communicating time-extended finite state machines (I/Ointerval structures). We use a compact symbolic representation to obtain efficient analysis algorithms. 1

2007

We present a performance analysis technique for distributed real-time systems in a setting where certain components are modeled in a purely functional manner, while the remaining components require additional modeling of state information. The functional models can be efficiently analyzed but have restricted expressiveness. On the other hand, state-based models are more expressive and offer a richer set of analyzable properties but are computationally more expensive to analyze. We show that by appropriately composing these two classes of models it is possible to leverage on their respective advantages. To this end, we propose an interface between components that are modeled using Real-Time Calculus [Chakraborty, Künzli and Thiele, DATE 2003] and those that are modeled using Event Count Automata [Chakraborty, Phan and Thiagarajan, RTSS 2005]. The resulting modeling technique is as expressive as Event Count Automata, but is amenable to more efficient analysis. We illustrate these advantages using a number of examples and a detailed case study. Processor Task Input Stream Service Model Load Model Concrete Instance Abstract Representation Abstract Processing Component to other computing or communication resources to other abstract components

Interface theories provide the foundation for formally defining and exploiting often implicitly made assumptions about the environment a component is interacting with. This paper develops a procedure for computing analytic input/output bounds for event streams consumed/emitted by the individual components of a system design, allowing to define state-less assume/guarantee (A/G) realtime interfaces for each component. However, contrary to existing work this paper extends interface definitions with properties to be met invariantly by any component that implements it. This allows to compute bounds of key performance metrics of the overall system design by solely considering the information provided by the enriched interfaces. This is important as it supports incremental, i. e. component-wise evolution of system designs for the following reason: given a consistent interface-based system description the interface-derived properties are invariant w. r. t. composition and substitution of components, as long as each state-based component implementation is conformant to its interface and the interfaces are compatible. This paper establishs the required consistency and conformance criteria and develops the machinery for carrying out the checks in an automatic fashion. Thereby it advocates a strictly compositional design approach and improves the scalability of statebased analysis methods. Sec. 5 presents an empirical evaluation of the framework. This is done (a) for demonstrating the efficiency of the proposed procedures, (b) for demonstrating that the interfacing of state-less and TA-based components allows for higher accuracy w. r. t. a systems performance metrics when compared to the pure analytic approach as developed in [12, 5] and (c) for demonstrating its scalability w. r. t. standard state-based analysis methodologies.

1991

Abstract The authors briefly review the time-constrained reactive automata (TRA) model and its use in the specification and verification of real-time embedded systems. Among its salient features is a fundamental notion of space and time that restricts the expensiveness of the model in a way that allows the specification of only reactive, spontaneous, and causal computation. Using the TRA formalism, there is no conceptual distinction between a system and a property; both are specified as formal objects.