Although silicon optical technology is still in its formative stages, and the more near-term application is chip-to-chip communication, rapid advances have been made in the development of on-chip optical interconnects. In this paper, we investigate the integration of CMOS-compatible optical technology to on-chip cache-coherent buses in future CMPs.While not exhaustive, our investigation yields a hierarchical opto-electrical system that exploits the advantages of optical technology while abiding by projected limitations. Our evaluation shows that, for the applications considered, compared to an aggressive all-electrical bus of similar power and area, significant performance improvements can be achieved using an opto-electrical bus. This performance improvement is largely dependent on the application's bandwidth demand and on the number of implemented wavelengths per optical waveguide. We also present a number of critical areas for future work that we discover in the course of our research. OPTICAL TECHNOLOGY OVERVIEWIn this work we consider on-chip modulator-based optical transmission (Figure 1), which comprises three major components: a transmitter, a waveguide, and a receiver. We briefly describe each component, and discuss technology trends in order to estimate the specifications of future designs. We propose one such design later in Section 3. TransmitterOptical transmission requires a laser source, a modulator, and a modulator driver (electrical) circuit. The laser source provides light to the modulator, which transduces electricalThe 39th Annual IEEE/ACM International Symposium on Microarchitecture (MICRO'06) 0-7695-2732

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This paper presents core fusion, a reconfigurable chip multiprocessor (CMP) architecture where groups of fundamentally independent cores can dynamically morph into a larger CPU, or they can be used as distinct processing elements, as needed at run time by applications. Core fusion gracefully accommodates software diversity and incremental parallelization in CMPs. It provides a single execution model across all configurations, requires no additional programming effort or specialized compiler support, maintains ISA compatibility, and leverages mature micro-architecture technology.

We present an all-optical approach to constructing data networks on chip that combines the following key features: (1) Wavelengthbased routing, where the route followed by a packet depends solely on the wavelength of its carrier signal, and not on information either contained in the packet or traveling along with it. (2) Oblivious routing, by which the wavelength (and thus the route) employed to connect a source-destination pair is invariant for that pair, and does not depend on ongoing transmissions by other nodes, thereby simplifying design and operation. And (3) passive optical wavelength routers, whose routing pattern is set at design time, which allows for area and power optimizations not generally available to solutions that use dynamic routing. Compared to prior proposals, our evaluation shows that our solution is significantly more power efficient at a similar level of performance.