HEX : Scaling honeycombs is easier than scaling clock trees

Abstract

We argue that a hexagonal grid with simple intermediate nodes is a robust alternative to buffered clock trees typically used for clock distribution in VLSI circuits, multi-core processors, and other applications that require accurate synchronization: Our HEX grid is Byzantine fault-tolerant, self-stabilizing, and seamlessly integrates with multiple synchronized clock sources, as used in multi-synchronous Globally Synchronous Locally Asynchronous (GALS) architectures. Moreover, HEX guarantees a small clock skew between neighbors even for wire delays that are only moderately balanced. We provide both a theoretical analysis of the worst-case skew and simulation results that demonstrate a very small average skew.