Controller re-specification to minimize switching activity in controller/data path circuits

This paper proposes a controller-based technique for minimizing switching activity in controller/data path circuits. Though the control signals in a register transfer level (RTL) implementation are fully specified, they can be re-specified under certain states/conditions when the data path components that they control need not be active. Unlike techniques that insert extra circuitry like transparent latches, controller re-specification is a low-overhead technique that merely reconfigures existing multiplexer networks and functional units to minimize activity in the data path. Hence, it is well suited to control-flow intensive designs, where power consumption in multiplexer networks forms a major component of the total power consumption. Our controller re-specification algorithm consists of constructing an activity graph for each data path component, identifying conditions under which the component need not be active, and re-labeling the activity graph resulting in re-specification of the corresponding control expressions. Application of the proposed technique to several RTL circuits demonstrated the ability to reduce the total (controller + data path) power consumption by up to 51.8% compared to the initial area-optimized implementations, with nominal area and delay overheads.