This paper deals with the system-level performance analysis and optimization of a class of digital systems we call mixed asynchronous-synchronous systems. In such a system, each computation module is either synchronous or asynchronous. The communication among all of the modules is assumed to be data driven. In order to adequately describe the timing of such architectures, we introduce a graph model called MASS, which is based on several extensions of timed marked graphs. The first extension is that the node set V is partitioned into synchronous and asynchronous nodes. A synchronous node can only fire at ticks of its local module clock. Based on these extensions, we analyze the behavior of MASS, in particular, period, periodicity, and maximal throughput rate. Finally, we introduce the optimization problem of assigning appropriate clock phases to synchronous nodes so to maximize the throughput rate of the resulting system. An exact solution as well as a polynomial time algorithm for nearly optimal phase assignment are presented.
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