Analyzing a controller of a power distribution unit using formal methods

This paper reports on the steps to formally verify the behavior of a controller of a power distribution unit (PDU) using the Analytical Software Design (ASD) method. The controller of the underlying PDU mainly controls the distribution of power and related network messages to a number of attached PCs and devices of X-ray systems. The behavioral correctness of the controller is critical in order to provide the clinical users the expected behavior of the system. As a result of the behavioral verification, two previously unrevealed errors were identified within the design of the PDU controller. According to the development team of the PDU the work has had a major benefit, locating errors that would have been hard to find otherwise by traditional testing

Fault Tolerance in Programmable Metasurfaces: The Beam Steering Case

Metasurfaces, the two-dimensional counterpart of metamaterials, have caught great attention thanks to their powerful control over electromagnetic waves. Recent times have seen the emergence of a variety of metasurfaces exhibiting not only countless functionalities, but also a reconfigurable or even programmable response. Reconfigurability, however, entails the integration of tuning and control circuits within the metasurface structure and, as this new paradigm moves forward, new reliability challenges may arise. This paper examines, for the first time, the reliability problem in programmable metamaterials by proposing an error model and a general methodology for error analysis. To derive the error model, the causes and potential impact of faults are identified and discussed qualitatively. The methodology is presented and instantiated for beam steering, which constitutes a relevant example for programmable metasurfaces. Results show that performance degradation depends on the type of error and its spatial distribution and that, in beam steering, error rates over 10% can still be considered acceptable

Robustness analysis of evolutionary controller tuning using real systems

A genetic algorithm (GA) presents an excellent method for controller parameter tuning. In our work, we evolved the heading as well as the altitude controller for a small lightweight helicopter. We use the real flying robot to evaluate the GA's individuals rather than an artificially consistent simulator. By doing so we avoid the ldquoreality gaprdquo, taking the controller from the simulator to the real world. In this paper we analyze the evolutionary aspects of this technique and discuss the issues that need to be considered for it to perform well and result in robust controllers

Evaluating the reliability of NAND multiplexing with PRISM

Probabilistic-model checking is a formal verification technique for analyzing the reliability and performance of systems exhibiting stochastic behavior. In this paper, we demonstrate the applicability of this approach and, in particular, the probabilistic-model-checking tool PRISM to the evaluation of reliability and redundancy of defect-tolerant systems in the field of computer-aided design. We illustrate the technique with an example due to von Neumann, namely NAND multiplexing. We show how, having constructed a model of a defect-tolerant system incorporating probabilistic assumptions about its defects, it is straightforward to compute a range of reliability measures and investigate how they are affected by slight variations in the behavior of the system. This allows a designer to evaluate, for example, the tradeoff between redundancy and reliability in the design. We also highlight errors in analytically computed reliability bounds, recently published for the same case study

Evaluating the reliability of NAND multiplexing with PRISM

Probabilistic-model checking is a formal verification technique for analyzing the reliability and performance of systems exhibiting stochastic behavior. In this paper, we demonstrate the applicability of this approach and, in particular, the probabilistic-model-checking tool PRISM to the evaluation of reliability and redundancy of defect-tolerant systems in the field of computer-aided design. We illustrate the technique with an example due to von Neumann, namely NAND multiplexing. We show how, having constructed a model of a defect-tolerant system incorporating probabilistic assumptions about its defects, it is straightforward to compute a range of reliability measures and investigate how they are affected by slight variations in the behavior of the system. This allows a designer to evaluate, for example, the tradeoff between redundancy and reliability in the design. We also highlight errors in analytically computed reliability bounds, recently published for the same case study

Formal development of control software in the medical systems domain

In this thesis we describe the effectiveness of applying a number of formal techniques to the development of industrial control software at Philips Healthcare. We demonstrate how these techniques were tightly incorporated to the industrial workflow and the issues encountered during the application. The work was established in an industrial context, dealing with real industrial projects and a real product concerning the development of interventional X-ray systems. The results are very conclusive in the sense that the used formal techniques could deliver substantially better quality code compared to the code developed in conventional development methods. Also, the results show that the productivity of the formally developed code is better than the productivity of code developed by projects at Philips Healthcare or projects reported worldwide. The thesis also includes a number of design and specification guidelines that assist constructing verifiable components using model checking. The guidelines were successful in designing and verifying a controller component developed at Philips Healthcare. Hence, the guidelines can provide an effective framework to design verifiable control components in industrial settings