11/2009 : On the Threat of Metastability in an Asynchronous Fault-Tolerant Clock Generation Scheme

RR Number

11/2009

Conference

15th IEEE International Symposium on Asynchronous Circuits and Systems

Author(s)

Gottfried Fuchs, Matthias Fuegger, Andreas Steininger

Abstract

Due to their handshake-based flow control, asynchronous circuits generally do not suffer from metastability issues as much as synchronous circuits do. We will show, however, that fault effects like single-event transients can force (sequential) asynchronous building blocks such as Muller C-Elements into a metastable state. By means of a fault-tolerant clock generation scheme, we will show that metastability could overcome conventional error containment boundaries, and that, ultimately, a single metastable upset could cause even a multiple Byzantine fault-tolerant system to fail. In order to quantify this threat, we performed accurate analytic modeling and simulation of the elastic pipelines, which are at the heart of our physical implementation of the fault-tolerant clocks. Our analysis results reveal that only transient pulses of some very pecific width can trigger metastable behavior, and that logical masking is still effective to some extent. Although in summary the probability of a metastable upset to propagate through a pipeline is hence fairly small, %it is definitely not negligible. We hence argue that a thorough metastability analysis is mandatory for circuits employed in high-dependability applications.

Bibtex

@inproceedings{FFS09:ASYNC09,
  author =       "Gottfried Fuchs and Matthias Fuegger and Andreas Steininger",
  title =        "On the Threat of Metastability in an Asynchronous Fault-Tolerant Clock Generation Scheme",
  booktitle =    {15th IEEE International Symposium on Asynchronous Circuits and Systems (ASYNC'09)},
  year =         {2009},
  month =        {May},
  pages = {127--136},
  address = {Chapel Hill, N. Carolina, USA}
}

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