Sebastian M. Sattler

Structure preserving modeling for safety critical systems

To warrant the functionality of safety critical circuits and systems, underlying functions have to be modeled in a fashion that preserves real-world structure. That means, it must be ensured that the formally derived functions of the real-world structure should be in consistent conformance with the functions generated by the structure itself. Conversely, from safety-related aspects, it is fatal, when the modeled functions behave different from their functions in reality. Thus, although structure preserving modeling is safety-relevant, the state of the art does not consistently handle the formal derivation and modeling of functions. Particularly this happens at asynchronous feedbacked structures, especially in favor of simplification and later optimization. Looking at a very elementary asynchronous feedback logic, we show that this problem of inconsistency is omnipresent, and that our demand for consistency can not be warranted by the state of the art methods. We propose a new modeling methodology that is capable to preserve the structure of asynchronous feedback.

Parallel Composition - A practical solution

A digital system exhibits a specific circuit structure and behavior. There are diverse methods of modeling structure and behavior, while manifold related to each other. In this paper we present a formalism to achieve an Automata Based theory for Composition (ABC) to model circuit structures in a unique manner. This means that the modeling automaton itself is unique for a given circuit structure (up to isomorphisms, e.g. alternative naming, symmetry). We get success on this approach by using a novel automata based parallel composition for discrete event systems named simultaneously-parallel composition. This composition establishes to automatically synthesize basic circuit entities to an overall circuit model, by preserving two axioms, synchronicity and asynchronicity. It is very suited to model and abstract complex hybrid systems with high safety and security issues. In addition, we show a novel representation of the behavior of the composed automata, embedding the states and transitions into open (2D) and closed (3D) diamonds, and discuss several theoretical and practical aspects.

Structure-preserving modeling of safety-critical combinational circuits

In this work, a representative combinational circuit is abstracted from transistor level to gate level and a structure preserving transition is carried out into a signal flow graph.

Mealy-to-moore transformation

In this paper we will show a method for transforming an asynchronously feed-backed Mealy machine into an equivalent Moore machine under use of dual-rail logic and the RS-Buffer. The resulting machine will be safe, stable and reproducable. We will further present a use-case to demonstrate the before mentioned transformation.

A dimensionality-reduction method for test data

When performing a separation of test results, coping with enormous high-dimensional data sets is necessary but problematic. The input of high-dimensional data, in which not a few elements are irrelevant or less relevant than others, usually lead to inadequate results. It is therefore useful to consult methods, which classify the individual dimensions of the data volumes according to their relevance. In this paper, we present the Principal Component Analysis (PCA) and a Self-developed non-linear Data Analysis (SEDA), used on a complete data collection, as classification methods. Both analyzes are clarified using the same example.

Verification and test of real circuits

For the verification and functional safety of real systems, e.g. of analog and digital circuits, the function associated with the real structure must be modelled with structural integrity ensured. This means that the consistency of the formally derived and modelled function with the function generated by the real structure must be ensured. In addition, the modelled function must exhibit a behavior that is equal to the function to be realized. In this article, a structure-preserving verification method is at first presented, and illustrated with a real digital circuit by verifying the circuit and respectively testing it for known, self-injected faults. The results are displayed as signal flow graphs by means of self-written program codes.

A New Approach for Modeling Inconsistencies in Digital-Assisted Analog Design

Safety critical circuits and systems require a specified function and real world structure to match each other. At the same time the functionality and the structure become more and more complex. This results in a high effort for design verification and test such that specification-oriented testing is getting more and more under pressure. In this paper we offer an approach to warrant the match between a specification and its structure by invertibly composing the corresponding “fingerprint” model. Conversely, the fingerprint warrants the match between specification and structure. We present a theoretical framework for creating the fingerprint from the specification and the structure, respectively, and demonstrate the parallel composition of fingerprints to an overall asynchronous feedback circuit system.

Theoretical framework for asynchronous feedback Network Under Balance (NUB)

We propose a theoretical framework for the associative composition of functionally stable asynchronous feedback Networks Under Balance (NUB) for safety critical systems. It is totally closed under inversion and decomposition; thus, it can be applied to many applications embedded in asynchronous environment. For this, we engage our Automata Based Composition (ABC); the given network can now be interpreted as an asynchronous feedback, functionally stable automaton. As the ABC is invertible, it can be exhaustively used for issues of test and diagnosis based on a correct-by-construction paradigm. To demonstrate the practical application of the theory, we present our laboratory setup of the theoretical framework as a proof of concept by developing a set of boundary conditions which lead to an implementation in a further step. For this purpose, we build up a network of microcontroller boards and a set of specialized firmwares implementing the different components of the NUB.

Parallel decomposition for safety-critical systems

In this paper we are dealing with the following problem definition: let be given a distributed assembly line composed of modules (digital units) and control units (ECU), linked via a bus interface. Now, consider the scenario where each ECU gets its input from the operating environment (e. g. analog-to-digital sensors) and feeds its output to different modules. The triggered states of these modules are control inputs for actuators. We show how to decompose the overall digital unit into sub-modules and the overall ECU into sub-ECUs. The components should operate in parallel. For consistency, such a decomposition approach needs to result in system level as well as in logic (digital) level in a one-to-one manner as possible. We keep this criterion by using a formalism, which has its representations both in system level and asynchronously digital circuit level, whereby the different types of representations are “uniquely glued” by algebraic automata based modeling. It is a decomposition based on axioms. It implies that on system level a digital unit - in general an arbitrary digital automaton - becomes subdivided into sub-functions, and on logic level, the structure of a module - generally an arbitrary asynchronously feed-backed digital circuitry - becomes decomposed into sub-structures. The decomposition has to warrant that the original control function of the ECU is represented by sub-ECUs. The method also takes care of functional hazards and risks using special techniques like filtering and freezing, which are inherently provided by the underlying axioms.

A Novel Formalism for Partially Defined Asynchronous Feedback Digital Circuits

In contrast to combinational logic and master clocked sequential logical, asynchronous feedback circuits are partially defined due to analogous meta-stabilities. We present a novel formalism to exactly explore this digitally assisted analog phenomenon in order to build up a representative test bench that is able to enforce race constraints (meta-stable behavior) for non-deterministics, instabilities as well as for oscillations in feedback structures. Further, we introduce our definitions for consistently modeling under state transition graphs, we provide all entities for modeling asynchronous feedback structures and state our proposed methodology with an exemplary asynchronous circuitry. The given example is explained at a high level of abstraction, all data for revision is provided, too. The approach seems to be capable to test for meta-stabilities, analog behavior in feedback digital structures.