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Buffered Steiner Trees for Difficult Instances Charles J. Alpert, Gopal Gandham, Milos Hrkic, John Lillis, Jiang Hu, Andrew B. Kahng, Bao Liu, Stephen T. Quay, Sachin S. Sapatnekar, Andrew J. Sullivan Late 1980s Min-Cost Steiner Tree Timing-driven Steiner Tree Early 1990s

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Buffered steiner trees for difficult instances l.jpg

Buffered Steiner Trees for Difficult Instances

Charles J. Alpert, Gopal Gandham, Milos Hrkic, John Lillis, Jiang Hu, Andrew B. Kahng, Bao Liu, Stephen T. Quay, Sachin S. Sapatnekar, Andrew J. Sullivan


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Late 1980s

Min-Cost Steiner Tree




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Present

Blockage Aware Trees


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Ripping out Synthesis Trees

  • Ugly pre-PD buffered trees

  • Inverted sinks

  • Trivial van Ginneken/Lillis change

    • Normal sinks: one positive candidate

    • Inverted sinks: one negative candidate

  • No big deal


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Or Is It?


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But Look What Happens



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Unrouted net

with placed pins

Construct

Steiner

Tree

Simultaneous

Tree Construction

And Buffer

Insertion

Dynamic

Programming

Buffer

Insertion

Buffered

Steiner

Tree

The Texas Two Step

Optimal


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C-Tree Algorithm

  • A-, B-, H-, O-, P-, trees taken

  • Cluster sinks by

    • Polarity

    • Manhattan distance

    • Criticality

  • Two-level tree

    • Form tree for each cluster

    • Form top-level tree





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Flat

C-Tree




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Difficult Steiner Instances

  • Polarity/size makes it hard

  • 3d trade-off

    • Timing

    • Buffers

    • Wire length

  • Work on it!


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