A highly configurable cache architecture for embedded systems

Energy consumption is a major concern in many embedded computing systems. Several studies have shown that cache memories account for about 50% of the total energy consumed in these systems. The performance of a given cache architecture is largely determined by the behavior of the application using that cache. Desktop systems have to accommodate a very wide range of applications and therefore the manufacturer usually sets the cache architecture as a compromise given current applications, technology and cost. Unlike desktop systems, embedded systems are designed to run a small range of well-defined applications. In this context, a cache architecture that is tuned for that narrow range of applications can have both increased performance as well as lower energy consumption. We introduce a novel cache architecture intended for embedded microprocessor platforms. The cache can be configured by software to be direct-mapped, two-way, or four-way set associative, using a technique we call way concatenation, having very little size or performance overhead. We show that the proposed cache architecture reduces energy caused by dynamic power compared to a way-shutdown cache. Furthermore, we extend the cache architecture to also support a way shutdown method designed to reduce the energy from static power that is increasing in importance in newer CMOS technologies. Our study of 23 programs drawn from Powerstone, MediaBench and Spec2000 show that tuning the cache's configuration saves energy for every program compared to conventional four-way set-associative as well as direct mapped caches, with average savings of 40% compared to a four-way conventional cache.