ABSTRACT
Traditionally, rectilinear Steiner minimum trees (RSMT) are widely used for routing estimation in design optimizations like floorplanning and physical synthesis. Since it optimizes wirelength, an RSMT may take a "non-direct" route to a sink, which may give the designer an unnecessarily pessimistic view of the delay to the sink.Previous works have addressed this issue through performance-driven constructions, minimum Steiner arborescence, and critical sink based Steiner constructions. Physical synthesis and routing flows have been reticent to adapt universal timing-driven Steiner constructions out of fear that they are too expensive (in terms of routing resource and capacitance). This paper studies several different performance-driven Steiner tree constructions in order to show which ones have superior performance.A key result is that they add at most 2%-4% extra capacitance, and are thus a promising avenue for today's increasingly aggressive performance-driven P&R flows.We demonstrate using a production P&R flow that timing-driven Steiner topologies can be easily embedded into an incremental routing subflow to obtain significantly improved timing (3.6% and 5.1% improvements in cycle time for two industry testcases) at practically no cost of wirelength or routability.
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Index Terms
- Timing-driven Steiner trees are (practically) free
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