Power Efficient Instruction Caches for Embedded Systems

Instruction caches typically consume 27% of the total power in modern high-end embedded systems. We propose a compiler-managed instruction store architecture (K-store) that places the computation intensive loops in a scratchpad like SRAM memory and allocates the remaining instructions to a regular instruction cache. At runtime, execution is switched dynamically between the instructions in the traditional instruction cache and the ones in the K-store, by inserting jump instructions. The necessary jump instructions add 0.038% on an average to the total dynamic instruction count. We compare the performance and energy consumption of our K-store with that of a conventional instruction cache of equal size. When used in lieu of a 8KB, 4-way associative instruction cache, K-store provides 32% reduction in energy and 7% reduction in execution time. Unlike loop caches, K-store maps the frequent code in a reserved address space and hence, it can switch between the kernel memory and the instruction cache without any noticeable performance penalty.