preferredExtensionDirection

Specifies the preferred direction for via extensions on the given layer. A via with extensions aligned to the preferredExtensionDirection of the lower and upper metal layers will have the lowest cost and will be preferred for routing over another via that has the same number of cuts and the same extension dimensions but violates this constraint.

This constraint is enabled by setting the db.use_separate_pref_ext_dir environment variable to true. By default, when db.use_separate_pref_ext_dir is set false, the preferred direction for the longer via extent is given by oaPreferredRoutingDirection.

When this constraint is set, the create_derived_vias command will create preferred/non-preferred via extensions based on this constraint.

preferredExtensionDirection Quick Reference

Constraint Type	Layer
Value Types	`StringAsIntValue`
Database Types	Design, Technology
Scope	design, foundry
Category	Routing

Value Type

preferredExtensionDirection constraints have a StringAsIntValue that is input as a string value and stored as an integer value as shown in the following table.

preferredExtensionDirection Values

String	Integer Value	Preferred Extension Direction:
`horzPrefRoutingDir`	2
`vertPrefRoutingDir`	3

Examples

In this example, the preferred extension direction for Metal3 is set to vertical.

setvar db.use_separate_pref_ext_dir true

set_layer_constraint -constraint preferredExtensionDirection -layer Metal3 -StringAsIntValue vertPrefRoutingDir

Virtuoso Space-based Router Constraint Reference
Product Version IC23.1, June 2023