Ingo Stierand

Using contract-based component specifications for virtual integration testing and architecture design

We elaborate on the theoretical foundation and practical application of the contract-based specification method originally developed in the Integrated Project SPEEDS [11], [9] for two key use cases in embedded systems design. We demonstrate how formal contract-based component specifications for functional, safety, and real-time aspects of components can be expressed using the pattern-based requirement specification language RSL developed in the Artemis Project CESAR, and develop a formal approach for virtual integration testing of composed systems based on such contract-specifications of subsystems. We then present a methodology for multi-criteria architecture evaluation developed in the German Innovation Alliance SPES on Embedded Systems.

Scheduling distributed real-time systems by satisfiability checking

We present a SAT-based approach to the task and message allocation problem of distributed real-time systems. In contrast to the heuristic approaches usually applied to this problem, our approach is guaranteed to find an optimal allocation for realistic task systems running on complex target architectures. Our method is based on the transformation of such scheduling problems into nonlinear integer optimization problems. The core of the numerical optimization procedure we use to discharge those problems is a solver for arbitrary Boolean combinations of integer constraints. Optimal solutions are obtained by imposing a binary search scheme on top of that solver. Experiments show the applicability of our approach to industrial-size task systems.

Real-time scheduling interfaces and contracts for the design of distributed embedded systems

A notion of interfaces based on regular languages for modelling and verification of real-time scheduling constraints was proposed in [5]. This initial notion considers task sets running on single resources, and simple deadline requirements. We extend the approach to enable support for complex task models running on systems with multiple resources. We show that this extension preserves all properties of the original notion. In addition, this extension gives rise to the application of our interfaces in the design of more complex systems, where components can be spread over distributed architectures. The work is complemented by an initial implementation that performs scheduling analysis for a relevant class of real-time interfaces. It actually constructs an interface for a system model if it satisfies a set of given real-time requirements.

Efficient Model-Checking for Real-Time Task Networks

Formal methods play an important role in the development of safety-critical systems. Their well-defined semantics can be employed for automatic formal system verification. Model-checking, a well-established formal verification technique, is however often restricted to an abstract level due to complexity reasons. For example, checking temporal system behavior with respect to hardware architectures and operating systems is often not possible.Real-time scheduling theory on the other hand provides efficient techniques for temporal analysis of real-world systems at architecture level.However, models used in real-time scheduling theory usually lack a semantics that is compatible to those used by formal specifications. This prevents to verify temporal system behavior at the architecture level with the same formal methods.We present an approach that combines a timed automata representation of task networks and efficient scheduling analysis techniques. Based on existing task network formalisms we define a consistent timed automaton model, and a mapping between both formalisms. We prove that the mapping induces behavioral equivalence of the models.We show an application of the approach by verifying task networks against Live Sequence Charts (LSC).

Automating the design flow for distributed embedded automotive applications: Keeping your time promises, and optimizing costs, too

We address the complete design flow from specification models of new automotive functions captured in Matlab-Simulink to their distributed execution on hierarchical bus-based electronic architectures hosting the release of already deployed automotive functions. We propose an automated design space exploration process resulting in a cost-optimized extension of the existing target hardware and an allocation of balanced task structures automatically derived from the specification model on this modified target hardware which is sufficient to guarantee both system-level timing requirements and deadlines extracted from the Matlab-Simulink specification model.

A proposal for real-time interfaces in SPEEDS

The SPEEDS project is aimed at making rich components models (RCM) into a mature framework in all phases of the design of complex distributed embedded systems. The RCM model is required to be expressive enough to cover the entire development process from requirements to code through design, and also capture both functional and non-functional aspects. In this paper we propose a language-based framework for real-time component interfaces in SPEEDS that is suitable at the ECU layer when a target processor has been identified, and WCET analysis done. We assume a discrete time model.

An optimal approach to the task allocation problem on hierarchical architectures

We present a SAT-based approach to the task and message allocation problem of distributed real-time systems with hierarchical architectures. In contrast to the heuristic approaches usually applied to this problem, our approach is guaranteed to find an optimal allocation for realistic task systems running on complex target architectures. Our method is based on the transformation of such scheduling problems into nonlinear integer optimization problems. The core of the numerical optimization procedure we use to discharge those problems is a solver for arbitrary Boolean combinations of integer constraints. Optimal solutions are obtained by imposing a binary search scheme on top of that solver. Experiments show the applicability of our approach to industrial-size task systems, which are mapped to heterogeneous hierarchical hardware architectures

State-based scheduling analysis for distributed real-time systems

The amount of system functions realized by software drastically increased in recent years. Software tasks of safety-critical systems like those in the automotive domain have to work in a timely manner. In such systems not only ordering of events but also timing properties like end-to-end deadlines are relevant for correctness and performance. Unfortunately, due to various inter-dependencies between software tasks the analysis of such properties becomes very complex. The state-of-the-art analysis approach considers only stateless system behaviors and relies on critical instances leading to very pessimistic results. Considering task inter-dependencies would result in more accurate results, though it negatively affects the scalability of the analysis.Our approach for scheduling analysis combines analytical and model checking methods. We consider the full state space of a system, where all interleavings and task dependencies are preserved. The state space is build in a compositional manner enabling a more scalable technique. For this, we introduce operations on the state spaces of resources, allowing the abstraction of irrelevant parts and the composition of state spaces. Based on the state space of each resource response times are determined, and timing and safety properties can be verified by means of reachability checks. The approach is demonstrated based on an example scenario.

An automated semantic-based approach for creating tasks from Matlab Simulink models

The approach proposed in this paper forms the front-end of a framework for the complete design flow from specification models of new automotive functions captured in Matlab Simulink to their distributed execution on hierarchical bus-based electronic architectures hosting the release of already deployed automotive functions. The process starts by deriving a task structure from a given Matlab Simulink model. Because the obtained network is typically unbalanced in the sense of computational node weights, nodes are melted following an optimization metric called cohesion where nodes are attracted by high communication density and repelled by high node weights. This reduces task-switching times by avoiding too lightweight tasks and relieves the bus by keeping inter-task communication low. This so-called Task Creation encloses the translation of the synchronous block diagram model of Simulink into a message-based task network formalism that serves as semantic base.

Evaluation of a state-based real-time scheduling analysis technique

The analysis of real-time properties is crucial in safety critical areas. Systems have to work in a timely manner to offer correct services. The analysis of timing properties is particularly difficult for distributed systems when complex interferences between individual tasks can occur. Considering only critical instances, as analytic approaches do, may deliver pessimistic results leading to higher production costs. In previous works we introduced a state-based approach to validate task-and end-to-end deadlines for distributed systems. To improve scalability and reduce the analysis time, the approach computes the state spaces of the individual resources in a compositional fashion. For this, abstraction and composition operations were defined to remove those parts of the inputs of resources which have no influence on the response times of the allocated tasks. In this work, a new abstraction technique is introduced for scenarios where event bursts occur. Further, we extend our approach for systems with cyclic dependencies among the resources. We evaluate our approach on a set of example scenarios and compare the results with the state-of-the-art tool Uppaal.