Optimal Bounded-Skew Steiner Trees to Minimize Maximum k-Active Dynamic Power

Abstract

Static Random-Access Memory (SRAM) is a key component of modern systems-on-chip (SOCs), appearing in on-chip cache memories, FIFOs, and register files. Increasingly, modern SOCs embed more memory hierarchies and various modules which require on-chip memory accesses due to the high cost of off-chip memory accesses, and the lower power density of memory fabrics that helps reduce need for “dark silicon”. For such memory-dominated chips, the product specification and electronic device designers will focus on the maximum power consumption across all power usage scenarios, where a portion of memories are active and others are turned off by clock/power gates. In this work, we introduce and study k-active dynamic power minimization in bounded-skew trees, where we seek to minimize the maximum dynamic power consumption when at most $k$ clock sinks are active. The sizes of SRAM blocks and the SOC die, relative to buffer distances in advanced nodes, effectively linearize clock power and wirelength of clock subtrees. We can therefore apply an extension of a flow-based ILP for bounded-skew Steiner tree construction, introduced at SLIP-2018 [1]. We also introduce and study k-consecutive-active dynamic power minimization in scenarios where only consecutively-indexed clock sinks can be active simultaneously. Further, we demonstrate how non-uniform underlying grids enable the ILP to more flexibly capture locations of terminals of trees. Finally, we study the potential tree cost reduction benefit of flexible clock source locations rather than fixed source locations. Our experimental results give new insight into the tradeoff of maximum k-( consecutive)-active dynamic power and wirelength, and of skew and wirelength.