Constructing stability-based clock gating with hierarchical clustering

Abstract

In modern designs, a complex clock distribution network is employed to distribute the clock signal(s) to all the sequential elements. As the functionality of these sequential elements depends heavily on usage scenarios, it is vital that the clock network is optimized for these scenarios. This paper introduces a clock network power optimization methodology based on design usage patterns and stability based clock gating. Specifically, whenever a register retains its value from the previous cycle, a clock gating implementation shuts off its clock and disables data loading to enable power reduction. We first introduce the notion of a stability pattern and its correlation with clock gating efficiency. Next, we introduce a methodology to identify efficient clock gating implementations. In this framework, a clustering algorithm leveraging stability patterns iteratively computes more effective gating implementations. Each implementation is evaluated further on area overhead and critical path delay. If it satisfies all criteria, it is implemented in the design; otherwise, it is sent back to the clustering algorithm to compute new clock gating implementations. Empirical results show 22.6% reduction in clock network power and 16.0% reduction in total power consumption. This confirms the practicality and robustness of the proposed methodology.