Reducing switching activity on datapath buses with control-signal gating

This paper presents a practical technique for saving power dissipation in large datapaths by reducing unnecessary switching activity on wide buses. Control signals on a datapath module are gated by the observability don´t care condition of the bus driven by that module to stop unnecessary switching activity on the bus. A methodology for automatic generation of gating conditions and synthesis of gated control signals from the RTL description of a design is presented. The technique has very low overheads in terms of area, power, and designer effort. It was applied to one of the integer execution units of a 64-bit super-scalar RISC microprocessor. Experimental results of running various application programs on the microprocessor show on an average 26.6% reduction in dynamic switching power in the integer execution unit, with no increase in path delays