Specialty Routing Constraints

There are special search hierarchies for tapers, shields, and other specialty routing.

Taper Constraints

Constraints that control tapering to or from the terms on a net are determined using the taper hierarchy shown in the following figure. If a taper constraint group is not assigned to an instTerm, it will inherit taper constraints from its term’s taper constraint group, then its net’s inputtaper or outputtaper constraint group, as appropriate, and so on. By default, the taper constraint group for the default multispec is the Global net default route spec.

Search Order for Taper Constraints

Shield Constraints

Most of the constraints that control shielding are assigned to the shield constraint group for the nets to be shielded, but they can also be assigned to the shield group for specific routes of those nets. This allows you to customize constraints for routes on a net. For example, you could specify a wider width shield wire around a particular route of a net.

Constraint Name	Search Order
`minWidth minSpacing tandemWidth tandemLayerAbove tandemLayerBelow`	`shield` group for the route `shield` group for the net `shield` group of the default multispec.
`shareShields`	Design route spec
`ignoreShieldingOnLayers`	Global net default route spec

Bus, Net Pair, and Matched Length Nets Constraints

The net groups for buses, net pairs and matched length nets are created using create_group. The search order for constraints that control the routing of these specialty net groups is shown below.

Constraint Name	Search Order
`minSpacing`	Reflexive constraint for the netGroup determines the spacing between nets within the netGroup TransReflexive constraint for the netGroup determines the spacing between nets in the netGroup and nets outside the netGroup Default constraint group for the net Default constraint group for the netGroup Global net default Design route spec Foundry route spec
`minWidth validRoutingLayers validRoutingVias minNumCut`	Default constraint group for the net Default constraint group for the netGroup Global net default Design route spec Foundry route spec
`lengthPatternAccordion lengthPatternEndRun lengthPatternOff lengthPatternRWAccordion lengthPatternTrombone routeMaxLength routeMinLength`	(Matched length net groups only) Default constraint group for the route Default constraint group for the net Default constraint group for the netGroup Global net default Design route spec Foundry route spec
`msMatchPerLayer msTolerance` (or `matchTolerance`)	(Matched length net groups only) Default constraint group for the netGroup Global net default Design route spec Foundry route spec

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