Ramifications of metastability in bit variables explored via Simpson’s 4-slot mechanism

Authors:
S. E. Paynter;N. Henderson;J. M. Armstrong
Affiliations:
MBDA UK Ltd., 5, BS34 7QW, Bristol, Filton, UK;Dependable Computing Systems Centre, BAE SYSTEMS, 5, University of Newcastle, BS34 7QW, Bristol, Filton, UK;University of Newcastle, Centre for Software Reliability, 5, University of Newcastle, BS34 7QW, Bristol, Filton, UK
Venue:
Formal Aspects of Computing
Year:
2004

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Abstract

Protocol descriptions often fail to take metastability into account. Metastability, however, can undermine protocols which depend on shared bits. In this paper a series of increasingly realistic models of bits are developed in CSP to explore the implications of metastability for Simpson’s 4-slot asynchronous communication mechanism. It is shown that the 4-slot mechanism with realistic bit models preserves data-coherence, freshness, and sequencing, and is Lamport-atomic. We demonstrate that metastability can undermine the correctness of protocols demonstrated correct on the assumption that bits are Lamport-safe; furthermore, realistic bit models can demonstrate that protocols are correct which Lamport-safe bit models would suggest were incorrect or impossible.