Empirical Study for Optimization of Power-Performance with On-Chip Memory

Power-performance (performance per uniform power consumption) recently has become a more important factor in modern highperformance microprocessors. In processor design, it is a well-known that off-chip memory access has a large impact on both performance and power consumption. On-chip memory is one solution for this problem, so that many processors such as the Renesas SH-4 and some ARM architecture type processors adopt on-chip memory, which resides on the same layer as the cache memory. In this study, the effectiveness of the on-chip memory in an SH-4 processor was quantitatively examined by directly measuring the real power of the processor. For these experiments, we proposed a method that made use of the on-chip memory for power reduction. The experimental results show that the optimization of data transfer using on-chip memory reduces EDP(energy delay product) by up to 15.2%. As an extension of on-chip memory, we have proposed an on-chip RAM architecture called SCIMA (software controllable integrated memory architecture) which enables DMA (direct memory access) transfer to the on-chip memory. According to the empirical data from the SH-4 processor, it was found that the additional DMA transfer using SCIMA reduces EDP by up to 26.3%.