rail

What it is ¶

rail(net) yields one row per net the engine treats as a power or ground rail. It covers both polarities: a supply net (+5V, VCC, 3V3) and a ground net (GND, VSS) both answer rail. A net qualifies when it is asserted-driven (a PWR_FLAG or equivalent directive), carries the design-wide global attribute, or its name reads as a rail or ground name.

net.ground is the ground-only subset of this relation: every net.ground row is also a rail row, but a supply rail answers rail and not net.ground. So rail(?n), not net.ground(?n) isolates the supply rails.

For hardware engineers ¶

These are the distribution nets, the ones a design taps rather than routes point-to-point. During a review you query rail to check that a rule’s rail set matches your intent: a signal net that shows up here has a name that collides with a supply convention or was marked driven when it should not be. It is also the join a protection or pull-up check needs, since “does this signal reach a rail” is the shape of many connectivity rules.

For software engineers ¶

A rail is a global singleton in the design graph (see ANALOGY.md): everything tied to +5V is one electrical node, and a reachability walk must not follow an edge into it or the whole graph collapses into one component. rail is the name of that singleton set. The relation is a filtered projection over Nets(), so rows are 1:1 with nets that pass the rail predicate, and an empty result means the read found no driven, global, or rail-named net.

Go projector ¶

railFacts in check/facts.go walks Model.Nets() and emits a row for each net where Model.IsPowerRail(name) holds. IsPowerRail (in check/locate.go) ORs four conditions: the power_driven attribute, the global attribute, isGroundName, and isPowerRailName (both from the active naming lexicon in check/rolenames.go). One row per rail net; empty when the design has no rail-named, global, or asserted-driven net.

Datalog ¶

List every power or ground rail:

rail(?n) => ?n

Find the components sitting on a rail (the loads and sources on power distribution):

rail(?n), component-on-net(?r, ?n) => ?r