THE OFFSET CUBE - A 3-DIMENSIONAL MULTICOMPUTER NETWORK TOPOLOGY USING THROUGH-WAFER OPTICS

Three-dimensional packaging technologies are critical for enabling ult ra-compact, massively parallel processors (MPPs) for embedded applicat ions. Through-wafer optical interconnect has been proposed as a useful technology for building ultra-compact MPPs since it provides a simpli fied mechanism for interconnecting stacked multichip substrates. This paper presents the offset cube, a new network topology designed to exp loit the packaging benefits of through-wafer optical interconnect in u ltra-compact MPP systems. We validate the offset cube's topological ef ficiency by developing deadlock-free adaptive routing protocols with m odest virtual channel requirements (only two virtual channels per link needed for full adaptivity). A preliminary analysis of router complex ity suggests these protocols can be efficiently implemented in hardwar e. We also present a 3D mesh embedding for the offset cube. Network si mulations show the offset cube performs comparably to a bidirectional 3D mesh of equal size under uniform; hot-spot, and trace-driven traffi c loads. While the offset cube is not proposed as a general replacemen t for the mesh topology, it leverages the benefits of through-wafer op tical interconnect more effectively than a mesh by completely eliminat ing chip-to-chip wires for data signals. Hence, the offset cube is an effective topology for interconnecting ultra-compact MCM-level MPP sys tems.