net.bus_like

What it is ¶

net.bus_like(net) yields one row per net that the engine treats as a shared-distribution node rather than a point-to-point signal: a ground plane, a net marked global, or any net whose fan-out is rail-scale. The series-reach walk (net.reaches) refuses to cross these nets, and this relation names that exact predicate. So “which nets are bus-scale?” is a query, not a constant buried in the walk.

A net is bus-like when any one of three holds:

• it carries the global attribute (a power/ground rail resolved design-wide), or
• its name reads as ground (GND, VSS, AGND, …), or
• more than 16 pins connect to it (rail-scale fan-out).

It is distinct from bus(label, kind). That relation reports a reader-detected unmodeled bus label (WS1-034), a syntactic construct that the reader saw but did not expand. net.bus_like is about a solved net’s electrical role, not a source-file token.

For hardware engineers ¶

You would never trace a signal through these nets to find what it drives. They are ground, global power distribution, and any net so heavily loaded that “what connects to it” is a distribution question, not a path question. During a review you query it to sanity-check that the walk-based rules (ESD, input-protection, feedback-probe) stop where you expect. Suppose a signal net you thought was point-to-point shows up here. Then its fan-out is higher than intended, or its name reads as a ground name.

For software engineers ¶

Think of a bus-like net as a global singleton in a dependency graph, where reachability analysis must not follow an edge into it, or the whole graph collapses into one component. The series-reach walk is a bounded BFS over pass elements (resistors, inductors, ferrites, fuses); net.bus_like is its stop set. The relation is a projection over Nets() with a boolean filter, so rows are 1:1 with nets that pass the predicate, and an empty result means the design is all point-to-point (no global-marked nets, no ground-named nets, nothing over the fan-out ceiling).

Go projector ¶

netBusLikeFacts in stdlib/relations/facts.go walks Model.Nets() and emits a row for each net where check.IsBusLike(m, n) holds. IsBusLike lives in core/check/reach.go, and the Reach walk’s stop check shares that single definition, so the relation and the walk cannot drift. One row per bus-like net; empty for a purely point-to-point design.

Datalog ¶

List every bus-like net:

net.bus_like(?n) => ?n

Find components sitting on a bus-like net (the loads on rails and ground):

net.bus_like(?n), component.net(?r, ?n) => ?r

Schematic ¶