FV encoding for low-power data I/O

The power consumed by I/O pins of a CPU is significant due to high capacitances associated with the pins. While highly effective techniques for reducing address bus switching exist, similarly effective techniques for data bus have not been developed. We have discovered a characteristic of values transmitted over the data bus according to which a small number of distinct values, called frequent values, account for 58-68% of transmissions over the external data bus. To exploit this characteristic we have developed a method for dynamic identification of frequent values and their use in encoding data values using FV (frequent value) encoding scheme. Our experiments show that FV encoding of 32 frequent values yields an average reduction of 42.7% (with onchip data cache) and 67.63% (without on-chip data cache) in data bus switching activity for SPEC95 benchmarks.