Hierarchical Value Cache Encoding for Off-Chip Data Bus

Off-chip data bus consumes a significant part of system power. Recent works use small caches (Value Cache) at each side of the off-chip data bus, and transmit cache indexes instead of data values to reduce bus switching activity. A larger VC has a higher VC hit rate, but it also incurs more switching activity on a VC hit. In this paper, we propose the hierarchical VC design concept that provides a good tradeoff between VC capacity and bus switching activity. Our experimental results show that the proposed hierarchlical VC design reduces the off-chip data bus energy by 60.2%.