Dominik Steenken

Multiobjective optimization for transistor sizing of CMOS logic standard cells using set-oriented numerical techniques

The design of resource efficient integrated circuits (IC) requires solving a minimization problem of more than one objective given as measures of available resources. This multiobjective optimization problem (MOP) can be solved on the smallest unit, the standard cells, to improve the performance of the entire IC. The traditional way of sizing the transistors of a standard logic cell does not focus on the resources directly. In this work transistor sizing is approached via an MOP and solved by set-oriented numerical techniques. A comparison of the Pareto optimal designs to elements of a commercial standard cell library indicates that for some gates the performance can even be significantly improved.

Timed Hazard Analysis of Self-healing Systems

Self-healing can be used to reduce hazards in embedded real-time systems which are applied in safety-critical environments. These systems may react to failures by a structural reconfiguration of the architecture during runtime. This means the exchange of components or the modification of the components’ connections, in order to avoid that a failure results in a hazard. This reaction is subject to hard real-time constraints because reacting too late does not yield the intended effects. Consequently, it is necessary to analyze the propagation of failures in the architectural configuration over time with respect to the structural reconfiguration. However, current approaches do not take into account the timing properties of the failure propagation and the structural reconfiguration. In this paper, we present a hazard analysis approach which specifically considers these timing properties. We illustrate our approach by an example case study from the RailCab project. Further, we demonstrate the scalability of the approach by experiments.

Bounded Model Checking of Graph Transformation Systems via SMT Solving

Bounded model checking (BMC) complements classical model checking by an efficient technique for checking error-freedom of bounded system paths. Usually, BMC approaches reduce the verification problem to propositional satisfiability. With the recent advances in SAT solving, this has proven to be a fast analysis.

Sound and complete abstract graph transformation

Graph transformation systems (GTS) are a widely used technique for the formal modeling of structures and structure changes of systems. To verify properties of GTS, model checking techniques have been developed, and to cope with the inherent infinity arising in GTS state spaces, abstraction techniques are employed. In this paper, we introduce a novel representation for abstract graphs (which are shape graphs together with shape constraints) and define transformations (execution steps) on abstract graphs. We show that these abstract transformations are sound and complete in the sense that they capture exactly the transformations on the concrete graph level. Furthermore, abstract transformation can be carried out fully automatically. We thus obtain an effectively computable “best transformer” for abstract graphs which can be employed in an abstraction-based verification technique for GTS.

Component-based timed hazard analysis of self-healing systems

Today, self-healing is increasingly used in embedded real-time systems, that are applied in safety-critical environments, to reduce hazards. These systems implement self-healing by reconfiguration, i.e., the exchange of system components during run-time that aims at stopping or removing failures. This reaction is subject to hard real-time constraints because reacting too late does not yield the intended effects. Consequently, it is necessary to analyze the propagation of failures over time and also take into account how the propagation of failures is changed by the reconfiguration. Current approaches do not analyze the propagation times of failures and the changes of structural reconfiguration on the failure propagation. We enhance our hazard analysis approach by extending our failure propagation models by propagation times and taking the systems real-time reconfiguration behavior into account. This allows to analyze how a reconfiguration with certain duration changes the failure propagation of a real-time system and thus whether it is able to prevent a hazard. We show the feasibility of our approach by an example case study from the RailCab project.

Methods of Improving the Dependability of Self-optimizing Systems

Various methods have been developed in the Collaborative Research Center 614 which can be used to improve the dependability of self-optimizing systems. These methods are presented in this chapter. They are sorted into two categories with regard to the development process of self-optimizing systems. On one hand, there are methods which can be applied during the Conceptual Design Phase. On the other hand, there are methods that are applicable during Design and Development.

Using shape analysis to verify graph transformations in model driven design

In model driven design processes, graph transformation systems are frequently used to model dynamic behaviour. Many complex models induce arbitratily large state spaces. Since the systems they model are often safety-critical, they need to be verified. Explicit modelchecking fails here, since it requires the construction of the entire state space. In this paper, we present a verification technique that can handle arbitrarily large state spaces. Furthermore we show that it can easily be integrated in existing model driven design processes.

Methods for the Design and Development

After the domain-spanning conceptual design, engineers from different domains work in parallel and apply their domain-specific methods and modeling languages to design the system. Vital for the successful design, are system optimization methods and the design of the reconfiguration behavior. The former methods enable the parametric adaption of the system’s behavior, e.g. an adaption of controller parameters, according to a current selection of the system’s objectives. The latter realizes structural adaption of the system’s behavior, e.g. the exchange of software or hardware parts. Altogether, this leads to a complex system behavior that is hard to overview. In addition, self-optimizing systems are used in safety-critical environments. Consequently, the system’s safety-critical behavior has to undergo a rigorous verification and testing process. Existing design methods do not address all of these challenges together. Indeed, a combination of established design methods for traditional technical systems with novel methods that focus on these challenges is necessary. In this chapter, we will focus on such new methods. We will introduce new system optimization and design methods to develop reconfigurations of the software and the microelectronics. In order to ensure the correctness of safety-critical functionality, we propose new testing methods and formal methods to ensure safety-properties of the software. We show how to apply virtual prototyping to deal with the complexity of self-optimizing systems and perform an early analysis of the overall system. As each domain applies its own modeling languages, the result of these methods are several overlapping models. In order to keep these domain-specific models consistent among all domains, we will introduce a new semi-automatic model synchronization technique. Each of these design methods are integrated with the reference process for the development of self-optimizing systems.