Congestion Analysis
Congestion occurs where routing demand exceeds available tracks or pin access, making legal detailed routing difficult or impossible.
Fix the generating cause—density, macro channels, pin concentration, net topology, or blockages—not only the visible overflow marker.
A narrow channel between two macros can appear empty yet remain unroutable because macro pins consume most available tracks at its entrance.
Physical Design flow
Follow each stage in sequence. Every stage produces information needed by the next.
Congestion Analysis—visualized
This technical view uses the actual structures and relationships associated with this stage, followed by its key terms.
Understand every concept
Overflow maps
What it is: Overflow maps is a core concept within Congestion Analysis. It describes the information, structure, or analysis engineers use at this stage of the Physical Design flow.
Why it matters: Understanding it helps you interpret the stage correctly, avoid incorrect assumptions, and connect the result to the next implementation or signoff step.
Where it fits: This topic belongs to module 9, Congestion Analysis, and its output supports the stages that follow.
Practical example: Engineer workflow: Locate hot spots in global-route and density maps. A narrow channel between two macros can appear empty yet remain unroutable because macro pins consume most available tracks at its entrance.
Root-cause analysis
What it is: Root-cause analysis is a core concept within Congestion Analysis. It describes the information, structure, or analysis engineers use at this stage of the Physical Design flow.
Why it matters: Understanding it helps you interpret the stage correctly, avoid incorrect assumptions, and connect the result to the next implementation or signoff step.
Where it fits: This topic belongs to module 9, Congestion Analysis, and its output supports the stages that follow.
Practical example: Engineer workflow: Separate macro-channel, cell-density, pin-access, and high-fanout causes. A narrow channel between two macros can appear empty yet remain unroutable because macro pins consume most available tracks at its entrance.
Placement and routing fixes
What it is: Placement and routing fixes is a core concept within Congestion Analysis. It describes the information, structure, or analysis engineers use at this stage of the Physical Design flow.
Why it matters: Understanding it helps you interpret the stage correctly, avoid incorrect assumptions, and connect the result to the next implementation or signoff step.
Where it fits: This topic belongs to module 9, Congestion Analysis, and its output supports the stages that follow.
Practical example: Engineer workflow: Apply spreading, padding, blockages, macro movement, or logic changes. A narrow channel between two macros can appear empty yet remain unroutable because macro pins consume most available tracks at its entrance.
Work through it step by step
- 1
Overflow maps
Locate hot spots in global-route and density maps.
- 2
Root-cause analysis
Separate macro-channel, cell-density, pin-access, and high-fanout causes.
- 3
Placement and routing fixes
Apply spreading, padding, blockages, macro movement, or logic changes.
- 4
Overflow maps
Re-place and reroute to compare overflow and timing.
Explore each topic
01Overflow maps
Understand the concept, connect it to the ASIC flow, study the report or behavior it produces, and apply it in a guided exercise. Check the result against the module goal before moving forward.
02Root-cause analysis
Understand the concept, connect it to the ASIC flow, study the report or behavior it produces, and apply it in a guided exercise. Check the result against the module goal before moving forward.
03Placement and routing fixes
Understand the concept, connect it to the ASIC flow, study the report or behavior it produces, and apply it in a guided exercise. Check the result against the module goal before moving forward.
Completion checklist
- ✓ Overflow decreases after the fix
- ✓ Timing does not regress severely
- ✓ Macro pin access remains open
- ✓ The solution survives detailed routing
Practise with open-source tools
These are official third-party GitHub projects selected for this learning path.