congestion_analysis

congestion_analysis
[ -gcell_width i_tracks ] 
[ -wrong_way ]

Description

Performs a congestion analysis on the active design and outputs a congestion summary to the Transcript area. If necessary, the congestion analysis builds the gcell grid, comprised of uniform square areas.

The congestion summary indicates the number of gcells of each type for each layer and statistics for each group including:

The number and percentage of overcongested gcells
The percentage of gcells grouped by the percentage of resources they are using
The percentage of gcells that have no capacity due to blockages (Blk%)

In general, it is not necessary to make an explicit congestion_analysis call during global routing. The global_route command automatically calls congestion_analysis with the default parameters. However, if you want to use a different gcell size, then you must invoke congestion_analysis with the desired gcell width, prior to global_route.

For a pictorial view of the congestion map, use show_congestion.

Arguments

`-gcell_width` i_tracks
	Specifies the width of the cell gcell, in tracks. If this argument is not given, Space-based Router and Chip Optimizer automatically determines the size of the gcells. If the specified `gcell_width` is too small for the size of the design and would create more gcells than can be represented, then the smallest possible gcell width will automatically be used instead.
`-wrong_way`	Allows global wrong-way routing in the entire design. By default, wrong-way global routing is not allowed. This option is useful if portions of a design are left unrouted because some pins require wrong-way access, and when routing channels are overcongested and could benefit if some portion switched its preferred routing direction. However, more searching is allowed if wrong-way routing is permitted, which increases the processing time.

Examples

The following example sets the gcell width to 10 tracks, then runs the global router.

congestion_analysis -gcell_width 10
global_route

The following is an example of congestion summary.

     Gcell summary
Layer/type  #Gcell  #Overcon %Overcon <10% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Blk%
---------------------------------------------------------------------------------------
metal1:cell     65         5  ( 7.69%)  9   6   1   9   3   3   3  23  13  20    0    0
metal1:edge     87         7  ( 8.05%) 34   8   1   8   0   0   0  16  12  11    0    0
metal2:cell     65         1  ( 1.54%)  9  10  12  15   4   6   1  15  15   7    0    0
metal2:edge     87         4  ( 4.60%) 32  10  14  10   0   1   0  14  11   0    0    0
metal2:down-via 65         0  ( 0.00%)
---------------------------------------------------------------------------------------

cell gcells occupy an area of the design.
edge gcells represent the region between two cell gcells on the same layer.
down-via gcells represent the region between two cell gcells on different layers.
#Gcell is the number of gcells of the given type for the given layer.
#Overcon is the number of layer/type gcells that are overcongested.
%Overcon is the percentage of layer/type gcells that are overcongested.
Each percentage grouping represents the number of layer/type gcells with congestion that meets the given heading percentage. In the example above, nine (9) metal1:cell gcells have less than 10% congestion, while twenty (20) are at least 90% congested.

Virtuoso Space-based Router Command Reference
Product Version IC23.1, September 2023