DRIM: a low power dynamically reconfigurable instruction memory hierarchy for embedded systems

Power consumption is of crucial importance to embedded systems. In such systems, the instruction memory hierarchy consumes a large portion of the total energy consumption. A well designed instruction memory hierarchy can greatly decrease the energy consumption and increase performance. The performance of the instruction memory hierarchy is largely determined by the specific application. Different applications achieve better energy-performance with different configurations of the instruction memory hierarchy. Moreover, applications often exhibit different phases during execution, each exacting different demands on the processor and in particular the instruction memory hierarchy. For a given hardware resource budget, an even better energy-performance may be achievable if the memory hierarchy can be reconfigured before each of these phases. In this paper, we propose a new dynamically reconfigurable instruction memory hierarchy to take advantage of these two characteristics so as to achieve significant energy-performance improvement. Our proposed instruction memory hierarchy, which we called DRIM, consists of four banks of on-chip instruction buffers. Each of these can be configured to function as a cache or as a scratchpad memory (SPM) according to the needs of an application and its execution phases. Our experimental results using six benchmarks from the MediaBench and the MiBench suites show that DRIM can achieve significant energy reduction.