Loosely Time-Triggered Architectures based on
Communication-by-Sampling
A. Benveniste, P. Caspi, M. Di Natale, C. Pinello, A. Sangiovanni
Vincentelli, and S. Tripakis
We address the problem of mapping a set of processes which communicate
synchronously on a distributed platform. The Time Triggered
Architecture (TTA) proposed by Kopetz for the communication mechanism
of a distributed platform offers a direct mapping that would preserve
the semantics of the specification. However, its exact implementation
may, at times, be problematic as it requires the distributed platform
to have the clocks of its components perfectly synchronized. We propose
as implementation architecture a relaxation of TTA called Loosely
Time-Triggered Architecture (LTTA), in which computing units perform
writes into and reads from the communication medium independently,
triggered by local, quasi-periodic but non synchronized, clocks. LTTA
offers some of the advantages of TTA with lower hardware cost and
greater flexibility. So far LTTA was studied for single directional
two-users communications over an LTT bus. General topology was not
studied. In this paper we propose a design flow that ensures semantics
preservation for an LTT communication network with arbitrary topology.
Key elements are two new protocols for clock regeneration and
predictive traffic shaping. Our approach relies on a mathematical Model
of Communication (MoC) that we describe in detail.