The earlier the better: a theory of timed actor interfaces

Programming embedded and cyber-physical systems requires attention not only to functional behavior and correctness, but also to non-functional aspects and specifically timing and performance. A structured, compositional, model-based approach based on stepwise refinement and abstraction techniques can support the development process, increase its quality and reduce development time through automation of synthesis, analysis or verification. Toward this, we introduce a theory of timed actors whose notion of refinement is based on the principle of worst-case design that permeates the world of performance-critical systems. This is in contrast with the classical behavioral and functional refinements based on restricting sets of behaviors. Our refinement allows time-deterministic abstractions to be made of time-non-deterministic systems, improving efficiency and reducing complexity of formal analysis. We show how our theory relates to, and can be used to reconcile existing time and performance models and their established theories

An Algebra of Synchronous Scheduling Interfaces

In this paper we propose an algebra of synchronous scheduling interfaces which combines the expressiveness of Boolean algebra for logical and functional behaviour with the min-max-plus arithmetic for quantifying the non-functional aspects of synchronous interfaces. The interface theory arises from a realisability interpretation of intuitionistic modal logic (also known as Curry-Howard-Isomorphism or propositions-as-types principle). The resulting algebra of interface types aims to provide a general setting for specifying type-directed and compositional analyses of worst-case scheduling bounds. It covers synchronous control flow under concurrent, multi-processing or multi-threading execution and permits precise statements about exactness and coverage of the analyses supporting a variety of abstractions. The paper illustrates the expressiveness of the algebra by way of some examples taken from network flow problems, shortest-path, task scheduling and worst-case reaction times in synchronous programming.Comment: In Proceedings FIT 2010, arXiv:1101.426

Assembling Components using SysML with Non-Functional Requirements

International audienceNon-functional requirements of component based systems are important as their functional requirements, therefore they must be considered in components assembly. These properties are beforehand specified with SysML requirement diagram. We specify component based system architecture with SysML block definition diagram, and component behaviors with sequence diagrams. We propose to specify formally component interfaces with interface automata, obtained from requirement and sequence diagrams. In this formalism, transitions are annotated with costs to specify non-functional property. The compatibility between components is performed by synchronizing their interface automata. The approach is explained with the example of the electric car CyCab, where the costs are associated to energy consumption of component actions. Our approach verifies whether, a set of components, when composed according to the system architecture, achieve their tasks by respecting their non-functional requirements

Compositional Schedulability Analysis of Hierarchical Real-Time Systems

Embedded systems are complex as a whole but consist of smaller independent modules interacting with each other. This structure makes them amenable to compositional design. Real-time embedded systems consist of realtime workloads having deadlines. Compositional design of such systems can be done using real-time components arranged in a scheduling hierarchy. Each component consists of some real-time workload and a scheduling policy for the workload. To simplify schedulability analysis for such systems, analysis should be done compositionally using interfaces that abstract timing requirement of components. To facilitate analysis of dynamically changing systems, the framework should also support incremental analysis. In this paper, we overview our approach to compositional and incremental schedulability analysis of hierarchical real-time systems. We describe a compositional analysis technique that abstracts resource requirement of components using periodic resource models. To support incremental analysis and resource bandwidth minimization, we describe an extension to this interface model. Each extended interface consists of multiple periodic resource models for different periods. This allows the selection of a periodic model that can schedule the system using minimum bandwidth. We also account for context switch overhead of components in these extended interfaces. We then describe an associative composition technique for such interfaces, that supports incremental analysis

Scheduling Induced Bounds and the Verification of Preemptive Real-Time Systems

Distributed real-time and embedded (DRE) systems have stringent constraints on timeliness and other properties whose assurance is crucial to correct system behavior. Our previous research has shown that detailed models of essential middleware mechanisms can be developed, composed, and for constrained examples verified tractably, using state of the art timed automata model checkers. However, to apply model checking to a wider range of real-time systems, particularly those involving more general forms of preemptive concurrency, new techniques are needed to address decidability and tractability concerns. This paper makes three contributions to research on formal verification and validation of DRE systems. First, it describes how bounded fair scheduling policies introduce a quasi-cyclic structure in the state space of multi-threaded real-time systems. Second, it shows that bounds on the divergence of threads\u27 execution can be determined for that quasi-cyclic structure, which then can be exploited to reduce the complexity of model checking. Third, it presents a case study involving progress-based fair scheduling of multi-threaded processing pipelines, with which the approach is evaluated

Verification of Component-based Distributed Real-time Systems

Component-based software architectures enable reuse by separating application-specific concerns into modular components that are shielded from each other and from common concerns addressed by underlying services. Even so, concerns such as invocation rates, execution latencies, deadlines, and concurrency and scheduling semantics still cross-cut component boundaries in many real-time systems. Verification of these systems therefore must consider how composition of components relates to timing, resource utilization, and other properties. However, existing approaches only address a sub-set of the concerns that must be modeled in component-based distributed real-time systems, and a new more comprehensive approach is thus needed. To address that need, this paper offers three contributions to the state of the art in verification of component-based distributed real-time systems: (1) it introduces a formal model called real-time component automata that combines and extends interface automata and timed automata models; (2) it presents new component composition operations for single-threaded and cooperative multitasking forms of concurrency; and (3) it describes how the composed models can be combined with task locations, a scheduling model, and a communication delay model, to generate a combined representation of the application components and supporting services that can be verified by existing model checkers. These contributions are embodied in an open-source tool prototype called the Real-time Component Model Translator (RTCMT)

The earlier the better: a theory of timed actor interfaces

Programming embedded and cyber-physical systems requires attention not only to functional behavior and correctness, but also to non-functional aspects and specifically timing and performance constraints. A structured, compositional, model-based approach based on stepwise refinement and abstraction techniques can support the development process, increase its quality and reduce development time through automation of synthesis, analysis or verification. For this purpose, we introduce in this paper a general theory of timed actor interfaces. Our theory supports a notion of refinement that is based on the principle of worst-case design that permeates the world of performance-critical systems. This is in contrast with the classical behavioral and functional refinements based on restricting or enlarging sets of behaviors. An important feature of our refinement is that it allows time-deterministic abstractions to be made of time-non-deterministic systems, improving efficiency and reducing complexity of formal analysis. We also show how our theory relates to, and can be used to reconcile a number of existing time and performance models and how their established theories can be exploited to represent and analyze interface specifications and refinement steps.\u

Interface Modeling for Quality and Resource Management

We develop an interface-modeling framework for quality and resource management that captures configurable working points of hardware and software components in terms of functionality, resource usage and provision, and quality indicators such as performance and energy consumption. We base these aspects on partially-ordered sets to capture quality levels, budget sizes, and functional compatibility. This makes the framework widely applicable and domain independent (although we aim for embedded and cyber-physical systems). The framework paves the way for dynamic (re-)configuration and multi-objective optimization of component-based systems for quality- and resource-management purposes

Formale Methoden zur Systemperformanzanalyse und -optimierung

With increasing system complexity, there is growing interest in using formal methods in wider range of systems to improve system predictability and determine system robustness to changes, enhancements and pitfalls. This paper gives an overview over a formal approach to system level performance modelling and analysis. A methodology is presented to cover distributed multiprocessor systems as well as multiprocessor systems on chip. The abstract modelling allows early design space exploration and optimization. We investigate an example multimedia application and optimize the usage of the shared memory to reach an optimal performance

Desafíos en el diseño de sistemas Ciber-Físicos

Los sistemas cyber-físicos ─Cyber-Physical Systems CPS─ es un proceso que integra la computación con los procesos físicos. Los computadores embebidos, el monitoreo de redes y el control de procesos físicos, usualmente tienen ciclos de retroalimentación en los que los procesos físicos afectan los cálculos, y viceversa. En este artículo se examinan los desafíos en el diseño de estos sistemas, y se plantea la cuestión de si la informática y las tecnologías de redes actuales proporcionan una base adecuada para ellos. La conclusión es que para mejorar los procesos de diseño de estos sistemas no será suficiente con elevar el nivel de abstracción o verificar, formalmente o no, los diseños en los que se basan las abstracciones de hoy. El potencial social y económico de los CPS es mucho mayor de lo que hasta el momento se ha pensado; en todo el mundo se están realizando grandes inversiones para desarrollar esta tecnología, pero los retos son considerables. Para aprovechar todo el potencial de los CPS se tendrán que reconstruir los procesos de las abstracciones informáticas y de las redes, y los procesos se deberán acoger en pleno a los principios de las dinámicas físicas y de la computación