用于低功耗时钟树综合的寄存器结群方法
Register Clustering Methodology for Low Power Clock Tree Synthesis
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摘要: 时钟网络的功耗在集成电路芯片总功耗中占有很大的比例。因此,在高性能集成电路设计中,时钟网络的功耗优化已经成为一个非常重要的目标。传统的方法是通过时钟绕线和缓冲器规划的优化策略解决这一问题。与此相比,本文提出了一种新的寄存器结群策略用来减少时钟网络的功耗。本文共提出了三种不同的寄存器结群算法,分别是KMR,KSR和GSR,并且对它们进行了综合的研究。同时,本文还提出了一个缓冲器分配算法,目的是用最小的功耗代价满足在寄存器簇内部的翻转速率要求。本文将提出的算法集成到一个经典的时钟树综合流程中,在ISPD2010 时钟网络综合竞赛的测试样例上对寄存器结群算法进行了验证。实验结果表明本文提出的三种寄存器结群算法均取得了20%以上的功耗优化,并且对时钟偏差和最大时延没有负面影响。作为三种算法中最有效的一个,GSR算法取得了31%的功耗优化,同时还取得了4%的时钟偏差优化和5%的最大时延优化。并且,集成了本文提出的寄存器结群算法之后,时钟树综合流程1的总运行时间减少了接近一个数量级。Abstract: Clock networks dissipate a significant fraction of the entire chip power budget. Therefore, the optimization for power consumption of clock networks has become one of the most important objectives in high performance IC designs. In contrast to most of the traditional studies that handle this problem with clock routing or buffer insertion strategy, this paper proposes a novel register clustering methodology in generating the leaf level topology of the clock tree to reduce the power consumption. Three register clustering algorithms called KMR, KSR and GSR are developed and a comprehensive study of them is discussed in this paper. Meanwhile, a buffer allocation algorithm is proposed to satisfy the slew constraint within the clusters at a minimum cost of power consumption. We integrate our algorithms into a classical clock tree synthesis (CTS) flow to test the register clustering methodology on ISPD 2010 benchmark circuits. Experimental results show that all the three register clustering algorithms achieve more than 20% reduction in power consumption without affecting the skew and the maximum latency of the clock tree. As the most effective method among the three algorithms, GSR algorithm achieves a 31% reduction in power consumption as well as a 4% reduction in skew and a 5% reduction in maximum latency. Moreover, the total runtime of the CTS flow with our register clustering algorithms is significantly reduced by almost an order of magnitude.