Semi-Automatic Compensation of the Propagation Delay in Fault-Tolerant Systems

T. Losert, W. Elmenreich, and M. Schlager (Austria)


Hard Real-Time Systems, Communication Model,Compensation of Propagation Delay, Precision of Distributed Clocks, Fault Tolerance.


In control systems the jitter is a major problem since in a time-varying system the theoretical results for anal ysis and design of time-invariant systems cannot be used directly. Reducing the jitter increases the stabil ity 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 topolo gies. Based on this model an algorithm is presented that allows to improve the precision of a set of dis tributed clocks by measuring the propagation delay of the communication lines 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.

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