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Buffer Insertion with Adaptive Blockage Avoidance

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Presentation on theme: "Buffer Insertion with Adaptive Blockage Avoidance"— Presentation transcript:

1 Buffer Insertion with Adaptive Blockage Avoidance
J. Hu C. J. Alpert S. T. Quay G. Gandham IBM Corporation 11/12/2018 Jiang Hu, et al., IBM

2 Buffer Insertion Improve timing Van Ginneken’s Algorithm
Drive long wire Shield load from critical path Van Ginneken’s Algorithm Given tree topology fixed Find optimal solution at fast speed Slack 24 33 73 -23 Slack 11/12/2018 Jiang Hu, et al., IBM

3 Buffer Blockage Slack 20 -11 Slack 26 -70 Slack Slack 11/12/2018
Jiang Hu, et al., IBM

4 Path vs. Branch Node 11/12/2018 Jiang Hu, et al., IBM

5 Previous Work on 2-pin Nets
Dynamic programming Zhou, et al., DAC 99 Graph based algorithm Jagannathan, et al., DAC 00 Lai and Wong, DAC 00 Minimum delay buffered path is found in polynomial time 11/12/2018 Jiang Hu, et al., IBM

6 Previous Work on Multi-pin Nets
RMP (Recursively Merging and Pruning), simultaneous tree construction and buffer insertion, Cong and Yuan, DAC 00 For buffer block planning Limited buffer sites, small nets High quality solution High complexity Tang, et al., ICCAD 01 Faster, Optimize delay Buffer block 11/12/2018 Jiang Hu, et al., IBM

7 Other Simultaneous Approaches
Lillis, et al., GLSV 96 Integrate P-Tree with van Ginneken’s algorithms Salek, et al., DAC 98, 99 Combine P-Tree with fanout optimization Search solution over the entire Extended Hanan Grid 11/12/2018 Jiang Hu, et al., IBM

8 Design Request #sinks 1 2-6 7-11 > 11 #nets 21541 24901 4107 2407
Medium size modern chip design RMP run for at least one week Tree + van Ginneken’s algorithm run for 1-2 hours Simultaneous approach: Good at optimizing a few critical nets, or small nets Cannot afford for many medium/large nets 11/12/2018 Jiang Hu, et al., IBM

9 Any Fast Approach? Sequential approach, TCAD 4/01
Steiner tree + make wires to avoid blockages + buffer insertion Fast Wire detour may be unnecessary, timing may become poor Slack 7 34 Slack 11/12/2018 Jiang Hu, et al., IBM

10 Challenge Good solution quality Fast speed
Close to van Ginneken’s algorithm Handle large nets and large number of blockages 11/12/2018 Jiang Hu, et al., IBM

11 Our Strategy Any technique somewhere between simultaneous and sequential methods? Construct Steiner tree as a guide Refine buffer solution search to limited region Allow flexibility to adjust tree topology Extend van Ginneken’s algorithm to incorporate tree adjustment with buffer insertion 11/12/2018 Jiang Hu, et al., IBM

12 RIATA Algorithm Repeater Insertion with Adaptive Tree Adjustment
Almost same as van Ginneken’s algorithm Extension: when a branch node n is blocked Find an unblocked n’ closest to n, between n and parent_node( n ) Generate candidate solutions buffered at n’ Propagate buffered solutions at n’ together with unbuffered solutions at n to parent_node( n ) 11/12/2018 Jiang Hu, et al., IBM

13 Example Steiner node/sink Subtree Subtree 11/12/2018
Jiang Hu, et al., IBM

14 Experiments on Large Nets
Slack (ps) 11/12/2018 Jiang Hu, et al., IBM

15 Slack Comparison with RMP
Slack (ps) 11/12/2018 Jiang Hu, et al., IBM

16 Comparison on CPU Time CPU (sec) #pins 11/12/2018
Jiang Hu, et al., IBM

17 Conclusion and Future Work
When construct buffered tree under blockage constraint for large design, either simultaneous or sequential method has significant weakness Our RIATA method can obtain a good solution at a fast speed Future work: optimize pin-pin path together with branch nodes 11/12/2018 Jiang Hu, et al., IBM

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