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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
2 2010 International Symposium on Physical Design March 15, 2010
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
3 2010 International Symposium on Physical Design March 15, 2010
Bill’s OpportunitiesASR-33 Teletype
1968: 8th grade
What Makes a Design Difficult to Route
4 2010 International Symposium on Physical Design March 15, 2010
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
5 2010 International Symposium on Physical Design March 15, 2010
What’s the Difference Between These Guys?
What Makes a Design Difficult to Route
6 2010 International Symposium on Physical Design March 15, 2010
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
7 2010 International Symposium on Physical Design March 15, 2010
Routing is From Venus, Congestion Analysis is From Mars
FloorplanningPlacement
Timing Closure
FloorplanningPlacement
Timing Closure
RoutingCongestion
Analysis
What Makes a Design Difficult to Route
8 2010 International Symposium on Physical Design March 15, 2010
Measuring Routing Quality (40-track per gcell)
What Makes a Design Difficult to Route
9 2010 International Symposium on Physical Design March 15, 2010
Routable gcell (75% full)
What Makes a Design Difficult to Route
10 2010 International Symposium on Physical Design March 15, 2010
Unroutable gcell (150% full) – 20 Nets of Overflow
What Makes a Design Difficult to Route
11 2010 International Symposium on Physical Design March 15, 2010
Example Congestion MapHorizontal Congestion Vertical Congestion
What Makes a Design Difficult to Route
12 2010 International Symposium on Physical Design March 15, 2010
Congestion Map with Better Physical SynthesisHorizontal Congestion Vertical Congestion
What Makes a Design Difficult to Route
13 2010 International Symposium on Physical Design March 15, 2010
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
14 2010 International Symposium on Physical Design March 15, 2010
Handling Routing Blockages
What Makes a Design Difficult to Route
15 2010 International Symposium on Physical Design March 15, 2010
50% Full or 95% Full?
What Makes a Design Difficult to Route
16 2010 International Symposium on Physical Design March 15, 2010
The Wire Stack
250nm 130nm 90nm 65nm 45nm32nm
What Makes a Design Difficult to Route
17 2010 International Symposium on Physical Design March 15, 2010
Resistance per mm
0
1
2
3
4
5
6
thin medium thick
65 nm45 nm32 nm
What Makes a Design Difficult to Route
18 2010 International Symposium on Physical Design March 15, 2010
Routing Tracks on 4X Metal
What Makes a Design Difficult to Route
19 2010 International Symposium on Physical Design March 15, 2010
Only 2 Tracks Left, but Not Congested
What Makes a Design Difficult to Route
20 2010 International Symposium on Physical Design March 15, 2010
Routing Tracks on 10X Metal
What Makes a Design Difficult to Route
21 2010 International Symposium on Physical Design March 15, 2010
Routing Tracks on 16X Metal
What Makes a Design Difficult to Route
22 2010 International Symposium on Physical Design March 15, 2010
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
23 2010 International Symposium on Physical Design March 15, 2010
Cross section of a gcell
1x
2x
4x
What Makes a Design Difficult to Route
24 2010 International Symposium on Physical Design March 15, 2010
Timing Closure Constrains The Router
Layer assignment / wire sizingassigns constraints for the router
What Makes a Design Difficult to Route
25 2010 International Symposium on Physical Design March 15, 2010
Is This a Congestion Problem?
1x
2x
4x
What Makes a Design Difficult to Route
26 2010 International Symposium on Physical Design March 15, 2010
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
27 2010 International Symposium on Physical Design March 15, 2010
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
28 2010 International Symposium on Physical Design March 15, 2010
Minimizing Wire Generally Improves CongestionBad placement Good placement
What Makes a Design Difficult to Route
29 2010 International Symposium on Physical Design March 15, 2010
Spread it Uniformly Doesn’t Always Work
What Makes a Design Difficult to Route
30 2010 International Symposium on Physical Design March 15, 2010
CRISP Progression
Initial Placement
Iteration 5 Iteration 10 Iteration 15
Horizontal Congestion
Vertical Congestion
What Makes a Design Difficult to Route
31 2010 International Symposium on Physical Design March 15, 2010
Effect of Timing Driven-PlacementInitial placement Timing-driven placement
What Makes a Design Difficult to Route
32 2010 International Symposium on Physical Design March 15, 2010
Effect of Timing Driven-Placement
Initial placement Timing-driven placement
What Makes a Design Difficult to Route
33 2010 International Symposium on Physical Design March 15, 2010
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
34 2010 International Symposium on Physical Design March 15, 2010
“Sitting” in the Student Section
Density
Rou
ting
diffi
culty
What Makes a Design Difficult to Route
35 2010 International Symposium on Physical Design March 15, 2010
Buffering Along A Global Route
What Makes a Design Difficult to Route
36 2010 International Symposium on Physical Design March 15, 2010
Buffer Packing
What Makes a Design Difficult to Route
37 2010 International Symposium on Physical Design March 15, 2010
Blockage Avoidance Routing
What Makes a Design Difficult to Route
38 2010 International Symposium on Physical Design March 15, 2010
The Corona Effect
What Makes a Design Difficult to Route
39 2010 International Symposium on Physical Design March 15, 2010
Corona Effect + Too Much Thick Metal
What Makes a Design Difficult to Route
40 2010 International Symposium on Physical Design March 15, 2010
Hot Spots versus Opens and Shorts
What Makes a Design Difficult to Route
41 2010 International Symposium on Physical Design March 15, 2010
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
42 2010 International Symposium on Physical Design March 15, 2010
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.
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