A Capacity Co-allocation Configurable Cache for Low Power Embedded Systems

Traditional level-one instruction caches and data caches for embedded systems typically have the same capacities. Configurable caches either shut down a part of the cache to suit applications needing a small cache or employ a large cache and high associativity for applications needing to reduce miss rate and energy. However, increasing associativity is energy-costly compared with increasing capacity. We have extended the traditional configurable cache and made the whole on-chip cache memory capacity available to both instruction and data caches. The capacity can then be co-allocated between the data and the instruction caches. Compared with way shutdown and way concatenation, the capacity co-allocation cache provides a better solution than increasing associativity. Four out of 17 benchmarks from Mibench benefit from the capacity co-allocation cache. Energy reduction can be up to 24%, with an average of 5%, compared to a traditional configurable cache.