net.ground

What it is ¶

net.ground(net) yields one row per net whose name reads as a ground node: GND or EARTH anywhere in the leaf name, or a VSS prefix. It is name-derived, since a directionless netlist carries the name as the only evidence that a net is ground.

net.ground is the ground-only subset of rail. rail covers both power and ground, because Model.IsPowerRail ORs the ground test into the rail test. So every net.ground net is also a rail net, and a rule reads rail(?r), not net.ground(?r) when it means “a supply rail, not ground.”

For hardware engineers ¶

Ground has to be told apart from a supply rail because rules treat the two differently. A grounded crystal case pin is not the Vdd pin of an active oscillator; a decoupling cap to ground is a different role than a cap between two supplies. During a review you query net.ground to confirm the engine recognises your ground naming, and you subtract it from rail to reason about supplies alone.

For software engineers ¶

net.ground is a filtered projection over Nets(), the same shape as rail. Rows are 1:1 with ground nets. An empty result means the read found no ground at all, which on a real design usually points at a naming convention the lexicon does not yet cover rather than a board with no ground.

A net is ground by NAME or by DECLARATION, whichever the source supports. Most formats carry only the name, and the naming lexicon exists to read it. IPC-2581 states it outright on LogicalNet/@netClass, so a net called N$17 can be authoritatively ground with nothing in the name to go on (WS1-051). The two sources are unioned at ingestion, not ranked, so a declaration never costs you a role the name would have found.

Go projector ¶

netGroundFacts in stdlib/relations/facts.go walks Model.Nets() and emits a row for each net where Model.IsGroundNet holds. That goes through check.NetHasRole, which prefers the role SET stamped at ingestion (ir.Net.roles, filled by classify.StampNetRoles) and falls back to matching the name when a net carries no roles at all. The naming lexicon’s IsGround matches GND, EARTH, or a VSS prefix on the hierarchy leaf, case-insensitive; the stamped set additionally carries any role the source declared. One row per ground net; empty when neither source finds one.

Datalog ¶

List every ground net:

net.ground(?n) => ?n

Isolate the supply rails by subtracting ground from the rail set:

rail(?n), not net.ground(?n) => ?n