Michael J. Pont

Fault-Tolerant Time-Triggered Communication Using CAN

The controller area network (CAN) protocol was originally introduced for automotive applications but is now also widely used in process control and many other industrial areas. In this paper, we present a low-cost redundancy-management scheme for replicated CAN channels that helps to ensure that clocks (and, hence, tasks) on the distributed nodes remain synchronized in the event of failures in the underlying communication channels, without the need for expensive or proprietary interface electronics. We argue that, when using this framework with duplicated channels, the probability of inconsistent message delivery drops to acceptable levels for a wide range of systems. Through an analysis of the protocol and a case study, we conclude that the creation of reliable, low-cost, distributed embedded systems using CAN is a practical possibility.

Reducing jitter in embedded systems employing a time-triggered software architecture and dynamic voltage scaling

We have previously demonstrated that use of an appropriate dynamic voltage scaling (DVS) algorithm can lead to a substantial reduction in CPU power consumption in systems employing a time-triggered cooperative (TTC) scheduler. In this paper, we consider the impact that the use of DVS has on the levels of both clock and task jitter in TTC applications. We go on to describe a modified DVS algorithm (TTC-jDVS) which can be used where low jitter is an important design consideration. We then demonstrate the effectiveness of the modified algorithm on a data set made up of artificial tasks and in a realistic case study.

Improving the performance of radial basis function classifiers in condition monitoring and fault diagnosis applications where ‘unknown’ faults may occur

This paper presents a novel technique which may be used to determine an appropriate threshold for interpreting the outputs of a trained radial basis function (RBF) classifier. Results from two experiments demonstrate that this method can be used to improve the performance of RBF classifiers in practical applications.

The maintenance and evolution of resource-constrained embedded systems created using design patterns

Most previous work on pattern-based software development has focused on the process of system creation rather than on the post-creation project phases (such as maintenance and evolution). In the study reported in this paper, we present the results from a short series of empirical studies in which we examined techniques for exchanging patterns used in an embedded design after the project had been completed. When exchanging patterns at this time, our aim was to identify the implementation of the pattern of interest in the system code and then substitute a suitable version of the replacement pattern. Findings are presented both from two small test projects, and from a more realistic case study. The results obtained suggest that this approach has considerable potential.

Implementation of H-Infinity Control Algorithms for Sensor-Constrained Mechatronic Systems Using Low-Cost Microcontrollers

This paper introduces a novel method which is intended to assist in the design and implementation of optimal H-infinity (H infin) algorithms in low-cost mechatronic applications. The particular problem considered is position control in a situation where there are both sensor-related uncertainties (caused by low-resolution sensors) and limited computational resources. The first part of the method presented in this paper describes how to design the H infin algorithm based on dynamic features of the sensor. The second part of the method involves finding a suitable numerical controller representation in order to reduce memory and CPU load. Evaluation of the method is based on empirical studies using three industrial sensors employed in a sub-acted robot. Results for a classic proportional integral derivative (PID) controller are included, in order to provide comparisons with the H infin approach. In the empirical evaluation, the PID implementation shows marginal stability when the low-resolution sensor is employed; by contrast, the H infin implementation is found to remain stable in the same circumstances.

Meeting real-time constraints using “sandwich delays”

This short paper is concerned with the use of patterns to support the development of software for reliable, resource-constrained, embedded systems. The paper introduces one new pattern (Sandwich Delay) and describes one possible implementation of this pattern for use with a popular family of ARM-based microcontrollers.

Towards a Generic “Single-Path Programming” Solution With Reduced Power Consumption

This paper was delivered at the Proceedings of the ASME 2007 International Design Engineering Technical Conferences & Computers and Information in Engineering Conference (IDETC/CIE 2007), September 4-7, 2007.

Improving the performance of CMFD applications using multiple classifiers and a fusion framework

In this paper, we demonstrate that the performance of a condition monitoring and fault diagnosis (CMFD) system may be improved by combining the outputs from three ‘primary’ classifiers using a novel, hybrid, data-fusion approach. The resulting classifier system involves four key processing stages. In Stage One, three diverse primary classifiers are employed. In Stage Two, the outputs from the primary classifiers are combined using majority voting. In Stage Three, any unclassified patterns from Stage Two are reassessed using Dempster-Shafer theory. Finally, in Stage Four, a simple rule base (‘expert system’) is used to integrate the results from the earlier stages. We demonstrate the effectiveness of this framework on a data set intended to allow the detection of static thermostatic valve faults in a diesel engine cooling system. Overall performance of the classifier system is shown to improve from approximately 89% (using the best of the primary classifiers) to approximately 99% (using the framework). In addition, the misclassification level of the original primary classifiers is shown to be approximately 10%, while the equivalent rate for the fusion classifier is approximately 1%. We go on to describe the application of the same classifier framework to a very different problem domain (medical diagnostics) and obtain a similar improvement in system performance. Here, overall performance of the classifier system is again shown to improve from approximately 87% (using the best of the primary classifiers) to approximately 99% (using the framework). In this case, the misclassification level of the original primary classifiers is approximately 12%, while the equivalent rate for the fusion classifier is approximately 1%. The results suggest that this framework may be appropriate for use in a range of application areas.

Applying MLP and RBF classifiers in embedded condition monitoring and fault diagnosis systems

In this paper, results are presented from a comprehensive series of studies aimed at assessing the suitability of multilayered perceptron (MLP) and radial basis function (RBF) networks for use in embedded, microcontroller-based, condition monitoring and fault diagnosis (CMFD) applications. Our assessment criteria include the performance of each classifier on a range of CMFD-related problems, such as situations where there may be multiple faults present simultaneously, or where ‘unknown’ faults may occur. In addition, the processor and memory requirements of each classifier are compared and discussed. On the basis of the results obtained in these studies, it is argued that each form of classifier has both strengths and weaknesses, and that neither is suitable for use in all CMFD applications. The paper concludes by demonstrating that, where memory and processor limits allow, the best performance may be obtained through use of a fusion classifier containing both MLP and RBF components.

A comparison of software-based techniques intended to increase the reliability of embedded applications in the presence of EMI

Abstract Corruption of the instruction pointer in an embedded computer system has been shown to be a common failure mode in the presence of electromagnetic interference, and previous investigators have suggested that the use of techniques such as ‘Function Tokens’ (FT) and ‘NOP Fills’ (NF) can reduce the impact of such failures. In this paper, both a statistical analysis and empirical tests of code from an embedded application are used to assess and compare these techniques. Two main results are presented. First, it is demonstrated that claims about the effectiveness of FT may neither be well founded nor generally applicable; specifically, it is concluded that rather than increasing system reliability, the use of FT will have the opposite effect. Second, it is demonstrated that NF may be easily applied in most embedded applications, and that the use of this approach can have a positive impact on system reliability.