component.net_count

What it is ¶

component.net_count(ref_des, count) yields one row per component, pairing its reference designator with the number of distinct nets its pins connect to. It is the part-side twin of net.pin_count. Every component gets a row, so a part wired to nothing answers 0 rather than being absent.

The count is of NETS, not pins. A resistor across VBUS and VBUS_F counts 2, and a jumper with both pins on GND counts 1.

For hardware engineers ¶

Most coverage questions about passives start with “for each two-terminal part”. A resistor, capacitor or diode on exactly two nets is the ordinary case, and the question is usually about both of those nets: are they both probeable, is one of them a rail, does the part sit between a connector and a clamp. This relation picks those parts out directly.

The other two values are worth a look during a review:

• 1 is a two-terminal part with both ends on the same net. That is either a deliberate short (a zero-ohm link, a DNP jumper) or a wiring mistake that shorts the part out.
• 0 is a part placed and wired to nothing, which is usually a leftover or a footprint that never got its nets.

For software engineers ¶

This is the degree of each component node in the design graph, counting distinct neighbouring nets rather than edges. It is a derived count of component.net. For every ref it equals the number of distinct ?n in component.net(ref, ?n), and a test holds the two to that. It is total over components, so an absent row means the ref is not in the design, never that it has no connections.

It exists because a rule body has no aggregation. “Parts on exactly two nets” otherwise needs three copies of component.net and a negation (agni issue 727).

Go projector ¶

componentNetCountFacts in stdlib/relations/facts.go walks Model.Components() and then each net’s connection list, as component.net does. It emits one row per ref with the count in the numeric slot. It reads connections rather than part-type pins, so it answers on a bare netlist that carries no pin data. A ref can appear in a connection with no component record. That ref still gets a row, citing nothing because there is no placement to cite. The count is dimensionless.

Datalog ¶

Every component and how many nets it touches:

component.net_count(?r, ?c) => ?r, ?c

Capacitors on exactly two nets, with both nets named. The ?a < ?b keeps one row per part rather than one per ordering:

component.class(?r, "capacitor"), component.net_count(?r, 2), component.net(?r, ?a), component.net(?r, ?b), ?a < ?b => ?r, ?a, ?b

Parts wired to nothing:

component.net_count(?r, 0) => ?r