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Minimizing power consumption is of paramount importance during the design of embedded (mobile computing) systems that come as systems-on-a-chip, since interdependencies between design characteristics like power, performance and area for various system parts (cores) are becoming increasingly influential. In this scenario, interfaces play a key role, since they allow one to control/exploit these interdependencies with the aim of meeting design constraints like power. In this paper, we present a comprehensive approach to explore this impact. We consider a whole system comprising a CPU, caches, a main memory and interfaces between those cores, and we demonstrate the high impact that an adequate adaptation between core parameters and interface parameters has in terms of power consumption. We find in particular that cache parameters and the configurations of cache buses have a significant impact in this respect. In addition, we make the important observation that optimizing for performance no longer implies that power is optimized as well in deep submicron technologies. Instead, we find that, especially for newer technologies, the relative interface power contribution increases, leading to scenarios where we obtain a real power/performance tradeoff. In summary, our explorations have revealed as yet uninvestigated interdependencies that represent the first step towards future efforts to optimize/adapt interfaces and caches in core-based systems for low-power designs.
Date of Conference: 7-11 Nov. 1999