A Formal Modeling Framework for Deploying Synchronous Designs on Distributed Architectures

Synchronous specifications are appealing in the design of large scale hardware and software systems because of their properties that facilitate verification and synthesis. When the target architecture is a distributed system, implementing a synchronous specification as a synchronous design may be inefficient in terms of both size (memory for software implementations or area for hardware implementations) and performance. A more elaborate implementation style where the basic synchronous paradigm is adapted to distributed architectures by introducing elements of asynchrony is, hence, highly desirable. This approach has to conjugate the desire of maintaining the theoretical properties of synchronous designs with the efficiency of implementations where the constraints imposed by synchrony are relaxed. Two interesting avenues have been recently pursued to achieve this goal: – Latency-insensitive protocols [9,10] motivated by hardware implementations, where long paths between the design components may introduce delays that force the overall clock of the system to run too slow in order to maintain synchronous behavior. This approach introduces additional elements in the design to allow the implementation to maintain the throughput that could have been achieved with communication delays of the same order of the clock of the subsystems at the price of additional latency. – Desynchronization [3,4,20] motivated by software implementations, where processes that compose the large scale system are locally implemented synchronously while their communication is implemented in an asynchronous style. This approach allows also to run each of the process at its own “speed”. By using the Lee and Sangiovanni-Vincentelli (LSV) tagged-signal model [19] as a common framework, we offer a comparative exposition of these approaches and we show their precise relationship. In doing so, we also provide some insight on the role of signal absence in synchronous, asynchronous, and globallyasynchronous locally-synchronous (GALS) design styles.