Predicting the effect of task jitter in real time control systems

Designing a real-time embedded control system requires designers to work through many steps, including simulation and full hardware implementation. Ideally, simulation can be used to quickly and cheaply check and optimise the system, but this requires simulation to match the hardware quite closely. Currently, there is no easy way to simulate task jitter, thus, a simulation is not available for such systems. To be safe, designers tend to choose expensive, over engineered hardware solutions in order to guarantee adequate system performance, but if cost is an issue, cheaper systems should be evaluated. Current hardware testing methods that adequately evaluate task jitter take considerable time and effort, and may result in a rework cycle with a new controller if cheaper options prove inadequate. This thesis provides a novel solution that overcomes these problems and will help designers select appropriate hardware + operating system(OS) platforms during the simulation phase.<br> The first research question is to find an appropriate way to capture task jitter from real controllers.  This resulted in a low-cost tool and the paper titled "Simulation is essential for embedded control systems with task jitter". <br> The next research question addresses the problem of simulating a control system using the task jitter information.  A novel method to model task jitter in MATLAB is developed that creates a variable z−1 delay.  This newly developed method has been verified by two control experiments: A motor speed controller and thermal controller. The experimental results show that simulation and hardware are closely matched given the same task jitter and has been published in two papers: "A new approach to clock jitter simulation in digital control system" and "Designing greener real-time controllers". <br> Some extended findings of the novel work have also been incorporated in other publications. The paper "A Low Budget Take-home Control Engineering Laboratory for Undergraduate" shows the benefit of the developed method by helping students understand the effects of hardware limitations in a control system at the simulation phase.  Another finding is presented in the paper "Predicting the effect of task jitter in digital control systems", which tests different types of task jitter and concludes that root-mean-square(RMS) value is sometimes a good predictor of the system performance.<br> A further research question aims to determine if simulation can provide insights that the testing of real hardware cannot provide.  The paper "Simulation is essential for embedded control systems with task jitter" records task jitter from two real hardware platforms and concludes that a real control system subject to task jitter might randomly and very occasionally show extreme behaviour which may be outside acceptable limits. This paper shows that the recorded jitter does not follow a classic Gaussian or uniform probability density function (PDF). Cases where the acceptable performance limits are exceeded would take a very long time to find using testing on real hardware but can be identified quickly using simulation.