Challenges in clockgating for a low power ASIC methodology

Gating the clock is an important technique used in low power design to disable unused modules of a circuit. Gating can save power by both preventing unnecessary activity in the logic modules as well as by eliminating power dissipation in the clock distribution network. There is an inherent pitfall though in implementing gating groups for hierarchical gated clock distribution because the groups are typically developed at the logic level with no information of the physical layout of the clocktree. Depending on the distribution of underlying sinks, maintaining gating groups can cause a wiring overhead that is potentially greater than the savings due to reduced switching. We look at modifications of zero-skew tree algorithms to consider both the physical and logical aspects of hierarchical gating. The algorithms are applied to data taken from a low power ASIC design. The best gated clocktree is created using both physical and logical information.