SoftCache: A Technique for Power and Area Reduction in Embedded Systems

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Fryman, Joshua Bruce
Lee, Hsien-Hsin Sean
Huneycutt, Chad Marcus
Farooqui, Naila F.
Mackenzie, Kenneth M.
Schimmel, D. E. (David E.)
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Explicitly software managed cache systems are postulated as a solution for power considerations in computing devices. The savings expected in a SoftCache lies in the removal of tag storage, associativity logic, comparators, and other hardware dedicated to memory hierarchies. The penalty lies in high cache-miss cost and additional instructions required to effect a cache model. In this paper, we characterize SoftCaches by placing them in the overall computing landscape, analyzing the energy and space trade-offs. We present results that indicate a SoftCache saves power and space over hardware caches. Based on the TSMC 0.25um process from MOSIS, we use schematic and layout representations of hardware and SoftCache models for comparison. Accounting for additional instructions executed and simplification of logic, we examine high SoftCache miss cost in relation to the overall system. For a 256KB "mode" change every 1.45 hours, the SoftCache exhibits 1% application slowdown for energy savings of 30% or more in a low-power device such as the SA-110 microprocessor used in PocketPC platforms.
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