what makes a design difficult to route · 2015-07-29 · bill gates. oct. 1955. steve jobs. feb....
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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
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What Does This Man and a Router Have in Common?
Young math whiz
Discovers computerprogramming
Drops out of Harvard
Starts Microsoft
Works really hard
Becomes very rich
What Makes a Design Difficult to Route
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Bill’s OpportunitiesASR-33 Teletype
1968: 8th grade
What Makes a Design Difficult to Route
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Some Math Whiz, Computer Programmer, Hard Working Guys
Bill GatesOct. 1955
Steve JobsFeb. 1955
Bill JoyNov. 1954
Scott McNealyNov. 1954
Eric SchmidtApr. 1955
What Makes a Design Difficult to Route
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What’s the Difference Between These Guys?
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
What Makes a Design Difficult to Route
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Routing is From Venus, Congestion Analysis is From Mars
FloorplanningPlacement
Timing Closure
FloorplanningPlacement
Timing Closure
RoutingCongestion
Analysis
What Makes a Design Difficult to Route
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Measuring Routing Quality (40-track per gcell)
What Makes a Design Difficult to Route
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Routable gcell (75% full)
What Makes a Design Difficult to Route
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Unroutable gcell (150% full) – 20 Nets of Overflow
What Makes a Design Difficult to Route
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Example Congestion MapHorizontal Congestion Vertical Congestion
What Makes a Design Difficult to Route
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Congestion Map with Better Physical SynthesisHorizontal Congestion Vertical Congestion
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
What Makes a Design Difficult to Route
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Handling Routing Blockages
What Makes a Design Difficult to Route
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50% Full or 95% Full?
What Makes a Design Difficult to Route
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The Wire Stack
250nm 130nm 90nm 65nm 45nm32nm
What Makes a Design Difficult to Route
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Resistance per mm
0
1
2
3
4
5
6
thin medium thick
65 nm45 nm32 nm
What Makes a Design Difficult to Route
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Routing Tracks on 4X Metal
What Makes a Design Difficult to Route
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Only 2 Tracks Left, but Not Congested
What Makes a Design Difficult to Route
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Routing Tracks on 10X Metal
What Makes a Design Difficult to Route
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Routing Tracks on 16X Metal
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!
What Makes a Design Difficult to Route
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Cross section of a gcell
1x
2x
4x
What Makes a Design Difficult to Route
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Timing Closure Constrains The Router
Layer assignment / wire sizingassigns constraints for the router
What Makes a Design Difficult to Route
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Is This a Congestion Problem?
1x
2x
4x
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
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
What Makes a Design Difficult to Route
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Minimizing Wire Generally Improves CongestionBad placement Good placement
What Makes a Design Difficult to Route
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Spread it Uniformly Doesn’t Always Work
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
What Makes a Design Difficult to Route
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Effect of Timing Driven-PlacementInitial placement Timing-driven placement
What Makes a Design Difficult to Route
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Effect of Timing Driven-Placement
Initial placement Timing-driven placement
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
What Makes a Design Difficult to Route
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“Sitting” in the Student Section
Density
Rou
ting
diffi
culty
What Makes a Design Difficult to Route
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Buffering Along A Global Route
What Makes a Design Difficult to Route
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Buffer Packing
What Makes a Design Difficult to Route
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Blockage Avoidance Routing
What Makes a Design Difficult to Route
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The Corona Effect
What Makes a Design Difficult to Route
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Corona Effect + Too Much Thick Metal
What Makes a Design Difficult to Route
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Hot Spots versus Opens and Shorts
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
What Makes a Design Difficult to Route
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What Does a Child Have in Common with a Router ?
Just because opportunity is provided, they may not take advantage.
We want to create opportunities to succeed.
We don’t really know what the best opportunities are.