The Jitter Margin and Its Application in the Design of Real-Time Control Systems

Based on recent advances in control theory, we propose the notion of jitter margin for periodic control tasks. The jitter margin isdefined as a function of the amount of constant delay in the controlloop, and it describes how much additional time-varying delay can betolerated before the loop goes unstable. Combined with schedulingtheory, the jitter margin can be used to guarantee the stability andperformance of the controller in the target system. It can also beused as a tool for assigning meaningful deadlines to control tasks.We discuss the need for best-case response-time analysis in thiscontext, and propose a simple lower bound under EDF scheduling.Finally, a control-scheduling codesign procedure is given, whereperiods are assigned iteratively to yield the same relativeperformance degradation for each control task