Activity-Aware Registers Placement for Low Power Gated Clock Tree Construction

Abstract

As power consumption of the clock tree dominates over 40% of the total power in modern high performance VLSI designs, measures must be taken to keep it under control. One of the most effective methods is based on clock gating to shut off the clock when the modules are idle. However, previous works on gated clock tree power minimization are most focused on clock routing and the improvements are often limited by the given registers placement. The purpose of this work is to navigate the registers during placement to further reduce the clock tree power based on clock gating. Our method simultaneously performs (1) activity-aware register clustering that reduces clock tree power not only by clumping registers into a smaller area, but pulling the registers with similar activity pattern close to shut off more time for the resultant subtrees; (2) timing and activity based net weighting that reduce net switching power by assigning a combination of activity and timing weights to the nets with higher switching rates or more critical timing; (3) gate control logic optimization that still set the gate enable signal high if a register is active for a number of consecutive clock cycles. Experimental results show that our approach is able to reduce the power and total wirelength of clock tree greatly with minimal overheads.