Controller-based power management for control-flow intensive designs

This paper presents a low-overhead controller-based power management technique that redesigns control logic to reconfigure the existing data path components under idle conditions so as to minimize unnecessary activity. Controller-based power management exploits the fact that though the control signals in a register-transfer level implementation are fully specified, they can be respecified under certain states conditions when the data path components that they control need not be active. We demonstrate that controller-based power management is often better-suited to control-flow intensive designs than comparable conventional power management techniques such as operand isolation. We present an algorithm to perform power management through controller redesign that consists of constructing an activity graph for each data path component, identifying conditions under which the component need not be active, and relabeling the activity graph resulting in redesign of the corresponding control expressions. We provide a comprehensive analysis of the potential side effects of controller-based power management on circuit delay, glitching activity at control and data path signals, and formation of false combinational cycles. Our algorithm avoids the above negative effects of controller-based power management to maximize power savings and minimize overheads. We present experimental results which demonstrate that 1) controller-based power management results in large power savings at minimal overheads for control-flow intensive designs, which pose several challenges to conventional power management techniques and 2) it is important to consider the various potential negative effects while performing controller-based saving power management in order to obtain maximal power savings.