6/2008 : Experimental Evaluation of the FlexRay Clock Synchronization Service

RR Number

6/2008

Comment

published version of RR 72/2007

Conference

20. Workshop für Testmethoden und Zuverlässigkeit von Schaltungen und Systemen

Author(s)

Eric Armengaud

Abstract

Clock synchronization mechanisms enable different nodes in a distributed system to agree on a common view of time. This is required, amongst other, to provide a consistent view of the environment. In case of FlexRay, this service is additionally required to enable collision-free communication. Clock synchronization works as follow: each node measures the current time base differences with the other participants to then update its local correction term and adapt its own time base. Testing this mechanism is confronted to two challenges: first, its distributed nature makes it impossible to partition the test and focus to one node in isolation; the whole system has to be considered. Moreover, each node implements locally a feedback loop and each participant influences the computation. Hence, the analysis complexity grows non-linearly both with the number of participants and with the number of computation steps considered. We present here a method for testing the FlexRay clock synchronization based on deterministic replay. This approach replays a traffic on the communication medium without correcting its time base, thus breaking the feedback loop and reducing the influence of the other participants. We illustrate our method with three campaigns to evaluate the robustness of this distributed algorithm with respect to quartz drifts. In particular, we will show that both the absolute value and the short term stability of the quartz drift have to be constrained to guarantee correct operation of the clock synchronization.

Bibtex

@article{ armengaud:2008-6,
  author =       "Eric Armengaud",
  title =        "Experimental Evaluation of the FlexRay Clock Synchronization Service",
  journal =      "20. Workshop für Testmethoden und Zuverlässigkeit von Schaltungen und Systemen",
  year =         "2008",
  month =        "Feb."
}

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