Fault-Tolerant Compensation of the Propagation Delay for Hard Real-Time Systems
Thomas Losert, Martin Schlager, and Wilfried Elmenreich
Institute of Computer Engineering, Vienna University of Technology, Vienna, Austria
In control systems the jitter is a relevant problem since the majority of theoretical results for analysis and design of time-invariant systems do not apply for time-variant systems. Reducing the jitter increases the stability of the closed control-loop thus leading to enhanced reliability. This paper presents a general model that can be applied to bus topologies as well as to star topologies. Based on this model an algorithm is presented that allows to improve the precision of a set of distributed clocks by measuring the propagation delay of the communication lines in a fault-tolerant way and compensating the jitter introduced by the propagation delay. Some fault-tolerant architectures already provide means for coping with propagation delays but require manually entering the values in a configuration-tool. With this algorithm the system supports this error-prone task by providing validity checks for the entered values or measuring these values automatically thus rendering this maintenance step obsolete.