Classifying Neighbor Nets

Prior to routing, you can set the crossTalkNeighborIndex constraint to classify the relationship between two net groups. The conduit router (croute) uses this constraint to determine the placement of wires and spacing between the nets. Nets can be considered to be good neighbors (route close to each other) or bad neighbors (keep apart).

To set the crossTalkNeighborIndex constraint, do the following:

Create two net groups of type cross_talk.

create_group -name s_group1Name -set d_setObj1 -type cross_talk
create_group -name s_group2Name -set d_setObj2 -type cross_talk

Create a constraint group.
```
create_constraint_group -name s_cg
```

Assign the constraint group to the two net groups at the group level.

assign_group_group -group1 s_group1Name -group2 s_group2Name -group_group_spec s_cg

Set the crossTalkNeighborIndex constraint.

set_constraint -constraint crossTalkNeighborIndex -IntValue i_Val -group s_cg

The valid crossTalkNeighborIndex values and descriptions are given in the following table.

crossTalkNeighborIndex Constraint Values

Value	Description
0	Good neighbors. Route groups close together. This can be used to half-shield nets with power rails as described in Shielding Group of Nets.
1	Neutral. No special relationship between the net groups.
2	Bad neighbors. Route groups apart as described in Avoiding Crosstalk

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