Bit-sliced datapath for energy-efficient high performance microprocessors

In the recent years, both power and performance have become important in the design of microprocessors. In this paper, we investigate exploiting the small-sized data values for energy-efficient high performance microprocessors. For this purpose, we bit-slice the execution core (which includes the functional units, register files, data caches, and forwarding logic), so that small portions of the data are operated upon in different bit-slices. The bit-slices operating upon the higher order bits are activated only if required, saving significant energy consumption. We also investigate further advantages facilitated by bit-slicing such as energy savings obtained by reducing the number of ports provided in the higher order bit-slices and by “shutting off” bit-slices to reduce leakage energy consumption. We found that a significant energy saving can be obtained in the register file (about 20%) and the Level-1 Data Cache (about 30%) with a negligible loss of only about 2% in the instruction throughput. Our studies also showed almost 20% savings in the register file leakage energy consumption, when the unwanted higher order bit-slices are “turned off”. Bit-slicing also helps in reducing the latency of the different hardware structures, which can facilitate clock speed improvements.