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What Makes a Design Difficult to Route
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What Makes A Design Difficult to Route Charles J. Alpert, Zhuo Li, - - PowerPoint PPT Presentation
What Makes A Design Difficult to Route Charles J. Alpert, Zhuo Li, - - PowerPoint PPT Presentation
IBM Corp. What Makes A Design Difficult to Route Charles J. Alpert, Zhuo Li, Michael Moffitt, Gi-Joon Nam, Jarrod Roy, Gustavo Tellez What Makes a Design Difficult to Route What Does This Man and a Router Have in Common? Young math whiz
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What Makes a Design Difficult to Route
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Bill’s Opportunities
ASR-33 Teletype 1968: 8th grade
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What Makes a Design Difficult to Route
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Some Math Whiz, Computer Programmer, Hard Working Guys Bill Gates
- Oct. 1955
Steve Jobs
- Feb. 1955
Bill Joy
- Nov. 1954
Scott McNealy
- Nov. 1954
Eric Schmidt
- Apr. 1955
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What Makes a Design Difficult to Route
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What’s the Difference Between These Guys?
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What Makes a Design Difficult to Route
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What Does a Router Have in Common with Bill Gates?
Take away the opportunity to succeed, and they won’t Give them the opportunity to succeed, and they will
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What Makes a Design Difficult to Route
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Routing is From Venus, Congestion Analysis is From Mars Floorplanning Placement Timing Closure Floorplanning Placement Timing Closure Routing Congestion Analysis
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What Makes a Design Difficult to Route
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Measuring Routing Quality (40-track per gcell)
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What Makes a Design Difficult to Route
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Routable gcell (75% full)
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What Makes a Design Difficult to Route
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Unroutable gcell (150% full) – 20 Nets of Overflow
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What Makes a Design Difficult to Route
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Example Congestion Map
Horizontal Congestion Vertical Congestion
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What Makes a Design Difficult to Route
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Congestion Map with Better Physical Synthesis
Horizontal Congestion Vertical Congestion
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What Makes a Design Difficult to Route
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Common Routing Metrics Number of Overflow Nets = Number of Nets Over 100% Congested Number of nets over 90% congested Number of nets over 80% congested Average congestion of 20% worst gcells
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What Makes a Design Difficult to Route
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Handling Routing Blockages
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What Makes a Design Difficult to Route
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50% Full or 95% Full?
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What Makes a Design Difficult to Route
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The Wire Stack
250nm 130nm 90nm 65nm 45nm 32nm
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What Makes a Design Difficult to Route
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Resistance per mm
1 2 3 4 5 6 thin medium thick 65 nm 45 nm 32 nm
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What Makes a Design Difficult to Route
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Routing Tracks on 4X Metal
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What Makes a Design Difficult to Route
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Only 2 Tracks Left, but Not Congested
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What Makes a Design Difficult to Route
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Routing Tracks on 10X Metal
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What Makes a Design Difficult to Route
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Routing Tracks on 16X Metal
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What Makes a Design Difficult to Route
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Is This Net Congested?
Different routers can and will report different routing metrics for the same exact global routes!
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What Makes a Design Difficult to Route
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Cross section of a gcell
1x 2x 4x
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What Makes a Design Difficult to Route
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Timing Closure Constrains The Router
Layer assignment / wire sizing assigns constraints for the router
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What Makes a Design Difficult to Route
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Is This a Congestion Problem?
1x 2x 4x
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What Makes a Design Difficult to Route
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Is It Routable? Avg 20% = 83.5 #nets > 100% = 532 #nets > 90% = 2785 Avg 20% = 89.1 #nets > 100% = 9532 #nets > 90% = 25785 Avg 20% = 78.2 #nets > 100% = 16 #nets > 90% = 753 Avg 20% = 81.7 #nets > 100% = 3942 #nets > 90% = 11880
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What Makes a Design Difficult to Route
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Congestion Analysis Versus Routing
Probabilistic Route Fast
Congestion Analysis
No Scenic Completely Scenic A Little Scenic Over Blockages Around Blockages May violate layer constraints Obey layer constraints Route Carefully Completely Scenic Around Blockages May violate layer constraints
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What Makes a Design Difficult to Route
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Minimizing Wire Generally Improves Congestion
Bad placement Good placement
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What Makes a Design Difficult to Route
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Spread it Uniformly Doesn’t Always Work
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What Makes a Design Difficult to Route
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CRISP Progression
Initial Placement Iteration 5 Iteration 10 Iteration 15 Horizontal Congestion Vertical Congestion
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What Makes a Design Difficult to Route
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Effect of Timing Driven-Placement
Initial placement Timing-driven placement
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What Makes a Design Difficult to Route
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Effect of Timing Driven-Placement
Initial placement Timing-driven placement
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What Makes a Design Difficult to Route
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Impact of More Efficient Area Usage
Avg 20%: 108.06 >90% nets: 37855 >100% nets: 21364 Avg 20%: 86.89 >90% nets: 7307 >100% nets: 1147
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What Makes a Design Difficult to Route
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“Sitting” in the Student Section
Density Routing difficulty
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What Makes a Design Difficult to Route
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Buffering Along A Global Route
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What Makes a Design Difficult to Route
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Buffer Packing
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What Makes a Design Difficult to Route
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Blockage Avoidance Routing
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What Makes a Design Difficult to Route
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The Corona Effect
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What Makes a Design Difficult to Route
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Corona Effect + Too Much Thick Metal
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What Makes a Design Difficult to Route
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Hot Spots versus Opens and Shorts
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What Makes a Design Difficult to Route
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What Makes a Design Difficult to Route?
- Bad floorplan
- Over packing dense logic
- Inefficient area minimization
- Over weighting for timing-driven placement
- Buffering too packed
- Over-constraining router
- Not capturing local routing isses
- Even if successful, don’t mess up timing too much
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What Makes a Design Difficult to Route
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