Multi-level clustering for clock skew optimization

Clock skew scheduling has been effectively used to reduce the clock period of sequential circuits. However, this technique may become impractical if a different skew must be applied for each memory element. This paper presents a new technique for clock skew scheduling constrained by the number of skew domains. The technique is based on a multi-level clustering approach that progressively groups flip-flops with skew affinity. This new technique has been compared with previous work, showing the efficiency in the obtained performance and computational cost. As an example, the skews for an OpenSparc with almost 16 K flip-flops and 500 K paths have been calculated in less than 5 minutes when using only 2 to 5 skew domains.