Concept of Routing Congestion

Hi friends,
What is the definition of congestion?
I heard that different tools put it differently. How is it for synopsys, cadence and magma?
What is the correct way?
What is placement congestion? Is it just the congestion at placement stage?
Why is it important?
What are the causes of congestion?
Types of congestion?
What are the different methods to analyze congestion?
How can we resolve congestion?
Is it always manual?
What are the different things tools can do to resolve it?
Can you please elaborate on what Magma tools do for the congestion aware design?

I will be very much thankful if you can reply me early.

Thanks,
Sowmya

Congestion in general referred to routing. Placement congestion is due to overlap of standard cells, it is called overlapping rather than called as congestion.
Routing congestion is difference between supplied and available tracks. A track is nothing but a routing resource. Tracks fill the entire core and routing channels are the empty space left after placing macros i.e., freezing on the floorplan. Every tool does routing in two stages. First routing is done trial routing which does not consider DRC rules, which gives an overall view of routing and congested nets. After you analyze the cause for congestion in your design, add density screen or change flooplan etc....As the Clock tree is built and timing is freezed, the tool does the detail routing in your design. This routing is done according to DRC and it is the final routing for your design.

Congestion reports is generated after each routing stages which shows the difference between supplied and demanded tracks or gcells. Use routing blockages or change placement of macros to avoid congestion.

Hi Sai Raj Kiran,
Thank you for your reply.
As far as I understood, what u explained is cadence perspective I think.
If you have any documents related to congestion or routing, it would be great if you share.

Thanks,
Sowmya

Hi,

What is role of a density screen in the context of congestion?
How it helps to avoid congestion?

Regards
Manoj

Density screen is applied to limit the density of standard cells in a area. This is helpful in reducing congestion due high pin density.