Kaiserslautern - Fachbereich Informatik
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A wide range of methods and techniques have been developed over the years to manage the increasing
complexity of automotive Electrical/Electronic systems. Standardization is an example
of such complexity managing techniques that aims to minimize the costs, avoid compatibility
problems and improve the efficiency of development processes.
A well-known and -practiced standard in automotive industry is AUTOSAR (Automotive
Open System Architecture). AUTOSAR is a common standard among OEMs (Original Equipment
Manufacturer), suppliers and other involved companies. It was developed originally with
the goal of simplifying the overall development and integration process of Electrical/Electronic
artifacts from different functional domains, such as hardware, software, and vehicle communication.
However, the AUTOSAR standard, in its current status, is not able to manage the problems
in some areas of the system development. Validation and optimization process of system configuration
handled in this thesis are examples of such areas, in which the AUTOSAR standard
offers so far no mature solutions.
Generally, systems developed on the basis of AUTOSAR must be configured in a way that all
defined requirements are met. In most cases, the number of configuration parameters and their
possible settings in AUTOSAR systems are large, especially if the developed system is complex
with modules from various knowledge domains. The verification process here can consume a
lot of resources to test all possible combinations of configuration settings, and ideally find the
optimal configuration variant, since the number of test cases can be very high. This problem is
referred to in literature as the combinatorial explosion problem.
Combinatorial testing is an active and promising area of functional testing that offers ideas
to solve the combinatorial explosion problem. Thereby, the focus is to cover the interaction
errors by selecting a sample of system input parameters or configuration settings for test case
generation. However, the industrial acceptance of combinatorial testing is still weak because of
the deficiency of real industrial examples.
This thesis is tempted to fill this gap between the industry and the academy in the area
of combinatorial testing to emphasizes the effectiveness of combinatorial testing in verifying
complex configurable systems.
The particular intention of the thesis is to provide a new applicable approach to combinatorial
testing to fight the combinatorial explosion problem emerged during the verification and
performance measurement of transport protocol parallel routing of an AUTOSAR gateway. The
proposed approach has been validated and evaluated by means of two real industrial examples
of AUTOSAR gateways with multiple communication buses and two different degrees of complexity
to illustrate its applicability.
Knowing the extent to which we rely on technology one may think that correct programs are nowadays the norm. Unfortunately, this is far from the truth. Luckily, possible reasons why program correctness is difficult often come hand in hand with some solutions. Consider concurrent program correctness under Sequential Consistency (SC). Under SC, instructions of each program's concurrent component are executed atomically and in order. By using logic to represent correctness specifications, model checking provides a successful solution to concurrent program verification under SC. Alas, SC’s atomicity assumptions do not reflect the reality of hardware architectures. Total Store Order (TSO) is a less common memory model implemented in SPARC and in Intel x86 multiprocessors that relaxes the SC constraints. While the architecturally de-atomized execution of stores under TSO speeds up program execution, it also complicates program verification. To be precise, due to TSO’s unbounded store buffers, a program’s semantics under TSO might be infinite. This, for example, turns reachability under SC (a PSPACE-complete task) into a non-primitive-recursive-complete problem under TSO. This thesis develops verification techniques targeting TSO-relaxed programs. To be precise, we present under- and over-approximating heuristics for checking reachability in TSO-relaxed programs as well as state-reducing methods for speeding up such heuristics. In a first contribution, we propose an algorithm to check reachability of TSO-relaxed programs lazily. The under-approximating refinement algorithm uses auxiliary variables to simulate TSO’s buffers along instruction sequences suggested by an oracle. The oracle’s deciding characteristic is that if it returns the empty sequence then the program’s SC- and TSO-reachable states are the same. Secondly, we propose several approaches to over-approximate TSO buffers. Combined in a refinement algorithm, these approaches can be used to determine safety with respect to TSO reachability for a large class of TSO-relaxed programs. On the more technical side, we prove that checking reachability is decidable when TSO buffers are approximated by multisets with tracked per address last-added-values. Finally, we analyze how the explored state space can be reduced when checking TSO and SC reachability. Intuitively, through the viewpoint of Shasha-and-Snir-like traces, we exploit the structure of program instructions to explain several state-space reducing methods including dynamic and cartesian partial order reduction.
Synapses play a central role in the information propagation in the nervous system. A better understanding of synaptic structures and processes is vital for advancing nervous disease research. This work is part of an interdisciplinary project that aims at the quantitative examination of components of the neuromuscular junction, a synaptic connection between a neuron and a muscle cell.
The research project is based on image stacks picturing neuromuscular junctions captured by modern electron microscopes, which permit the rapid acquisition of huge amounts of image data at a high level of detail. The large amount and sheer size of such microscopic data makes a direct visual examination infeasible, though.
This thesis presents novel problem-oriented interactive visualization techniques that support the segmentation and examination of neuromuscular junctions.
First, I introduce a structured data model for segmented surfaces of neuromuscular junctions to enable the computational analysis of their properties. However, surface segmentation of neuromuscular junctions is a very challenging task due to the extremely intricate character of the objects of interest. Hence, such problematic segmentations are often performed manually by non-experts and thus requires further inspection.
With NeuroMap, I develop a novel framework to support proofreading and correction of three-dimensional surface segmentations. To provide a clear overview and to ease navigation within the data, I propose the surface map, an abstracted two-dimensional representation using key features of the surface as landmarks. These visualizations are augmented with information about automated segmentation error estimates. The framework provides intuitive and interactive data correction mechanisms, which in turn permit the expeditious creation of high-quality segmentations.
While analyzing such segmented synapse data, the formulation of specific research questions is often impossible due to missing insight into the data. I address this problem by designing a generic parameter space for segmented structures from biological image data. Furthermore, I introduce a graphical interface to aid its exploration, combining both parameter selection as well as data representation.
Distributed systems are omnipresent nowadays and networking them is fundamental for the continuous dissemination and thus availability of data. Provision of data in real-time is one of the most important non-functional aspects that safety-critical networks must guarantee. Formal verification of data communication against worst-case deadline requirements is key to certification of emerging x-by-wire systems. Verification allows aircraft to take off, cars to steer by wire, and safety-critical industrial facilities to operate. Therefore, different methodologies for worst-case modeling and analysis of real-time systems have been established. Among them is deterministic Network Calculus (NC), a versatile technique that is applicable across multiple domains such as packet switching, task scheduling, system on chip, software-defined networking, data center networking and network virtualization. NC is a methodology to derive deterministic bounds on two crucial performance metrics of communication systems:
(a) the end-to-end delay data flows experience and
(b) the buffer space required by a server to queue all incoming data.
NC has already seen application in the industry, for instance, basic results have been used to certify the backbone network of the Airbus A380 aircraft.
The NC methodology for worst-case performance analysis of distributed real-time systems consists of two branches. Both share the NC network model but diverge regarding their respective derivation of performance bounds, i.e., their analysis principle. NC was created as a deterministic system theory for queueing analysis and its operations were later cast in a (min,+)-algebraic framework. This branch is known as algebraic Network Calculus (algNC). While algNC can efficiently compute bounds on delay and backlog, the algebraic manipulations do not allow NC to attain the most accurate bounds achievable for the given network model. These tight performance bounds can only be attained with the other, newly established branch of NC, the optimization-based analysis (optNC). However, the only optNC analysis that can currently derive tight bounds was proven to be computationally infeasible even for the analysis of moderately sized networks other than simple sequences of servers.
This thesis makes various contributions in the area of algNC: accuracy within the existing framework is improved, distributivity of the sensor network calculus analysis is established, and most significantly the algNC is extended with optimization principles. They allow algNC to derive performance bounds that are competitive with optNC. Moreover, the computational efficiency of the new NC approach is improved such that this thesis presents the first NC analysis that is both accurate and computationally feasible at the same time. It allows NC to scale to larger, more complex systems that require formal verification of their real-time capabilities.
In der aktuellen technologischen Entwicklung spielen verteilte eingebettete Echtzeitsysteme eine immer zentralere Rolle und werden zunehmend zum Träger von Innovationen. Durch den hiermit verbundenen steigenden Funktionsumfang der verteilten Echtzeitsysteme und deren zunehmenden Einsatz in sicherheitsrelevanten Anwendungsgebieten stellt die Entwicklung solcher Systeme eine immer größere Herausforderung dar. Hierbei handelt es sich einerseits um Herausforderungen bezogen auf die Kommunikation hinsichtlich Echtzeitfähigkeit und effizienter Bandbreitennutzung, andererseits werden geeignete Methoden benötigt, um den Entwicklungsprozess solcher komplexen Systeme durch Tests und Evaluationen zu unterstützen und zu begleiten. Die hier vorgestellte Arbeit adressiert diese beiden Aspekte und ist entsprechend in zwei Teile untergliedert.
Der erste Teil der Arbeit beschäftigt sich mit der Entwicklung neuer Kommunikationslösungen, um den gestiegenen Kommunikationsanforderungen begegnen zu können. So erfordert die Nutzung verteilter Echtzeitsysteme im Kontext sicherheitsrelevanter Aufgaben den Einsatz zeitgetriggerter Kommunikationssysteme, die in der Lage sind, deterministische Garantien bezüglich der Echtzeitfähigkeit zu gewähren. Diese klassischen auf exklusiven Reservierungen basierenden Ansätze sind jedoch gerade bei (seltenen) sporadischen Nachrichten sehr ineffizient in Bezug auf die Nutzung der Bandbreite.
Das in dieser Arbeit verwendete Mode-Based Scheduling with Fast Mode-Signaling (modusbasierte Kommunikation) ist ein Verfahren zur Verbesserung der Bandbreitennutzung zeitgetriggerter Kommunikation, bei gleichzeitiger Gewährleistung der Echtzeitfähigkeit. Um dies zu ermöglichen, erlaubt Mode-Based Scheduling einen kontrollierten, slotbasierten Wettbewerb, welcher durch eine schnelle Modussignalisierung (Fast Mode-Signaling) aufgelöst wird. Im Zuge dieser Arbeit werden verschiedene robuste, zuverlässige und vor allem deterministische Realisierungen von Mode-Based Scheduling with Fast Mode-Signaling auf Basis existierender drahtgebundener Kommunikationsprotokolle (TTCAN und FlexRay) vorgestellt sowie Konzepte präsentiert, welche eine einfache Integration in weitere Kommunikationstechnologien (wie drahtlose Ad-Hoc-Netze) ermöglichen.
Der zweite Teil der Arbeit konzentriert sich nicht nur auf Kommunikationsaspekte, sondern stellt einen Ansatz vor, den Entwicklungsprozess verteilter eingebetteter Echtzeitsysteme durch kontinuierliche Tests und Evaluationen in allen Entwicklungsphasen zu unterstützen und zu begleiten. Das im Kontext des Innovationszentrums für Applied Systems Modeling mitentwickelte und erweiterte FERAL (ein Framework für die Kopplung spezialisierter Simulatoren) bietet eine ideale Ausgangsbasis für das Virtual Prototyping komplexer verteilter eingebetteter Echtzeitsysteme und ermöglicht Tests und Evaluationen der Systeme in einer realistisch simulierten Umgebung. Die entwickelten Simulatoren für aktuelle Kommunikationstechnologien ermöglichen hierbei realistische Simulationen der Interaktionen innerhalb des verteilten Systems. Durch die Unterstützung von Simulationssystemen mit Komponenten auf unterschiedlichen Abstraktionsstufen kann FERAL in allen Entwicklungsphasen eingesetzt werden. Anhand einer Fallstudie wird gezeigt, wie FERAL verwendet werden kann, um ein Simulationssystem zusammen mit den zu realisierenden Komponenten schrittweise zu verfeinern. Auf diese Weise steht während jeder Entwicklungsphase ein ausführbares Simulationssystem für Tests zur Verfügung. Die entwickelten Konzepte und Simulatoren für FERAL ermöglichen es, Designalternativen zu evaluieren und die Wahl einer Kommunikationstechnologie durch die Ergebnisse von Simulationen zu stützen.