Tunable and Energy Efficient Bus Encoding Techniques

Off-Chip buses constitute a significant portion of the total system power in embedded systems. Many research works have focused on reducing power consumption in the off-chip buses. While numerous techniques exist for reducing bus power in address buses, only a handful of techniques have been proposed for off-chip data bus power reduction. In this paper, we propose two novel data bus encoding schemes to reduce power consumption in the data buses. The first scheme called Variable Length Value Encoder (VALVE) is capable of detecting and encoding variable lengths of repeated bit patterns in the data. The second technique called Tunable Bus Encoder (TUBE) encodes repetition in contiguous as well as noncontiguous bit positions of data values. Both schemes require just one external control signal to encode data values. TUBE is the first proposed hardware-based bus encoding scheme capable of detecting and encoding both contiguous and noncontiguous bit patterns of varying widths. Experimental evaluation on a large set of benchmarks shows an energy reduction of 58 percent and 60 percent on average for VALVE and TUBE, respectively. We evaluate the performance penalty incurred due to the codec delay and it is found to be 0.45 percent of the total program execution time. We also quantify our hardware overhead in terms of area, delay, and energy consumption. In 0.18 mum technology, VALVE and TUBE require a modest area of 0.0486 mm² and 0.0521 mm², respectively.