net.has_test_point

What it is ¶

net.has_test_point(net) holds for each net with at least one test point on it. A test point here is any component classified test_point, which by default is a part whose reference designator starts with TP, and a project can extend that class in its naming conventions. A net carrying three test points answers once.

The things it does not count matter as much. A connector pin, an exposed pad, or a via planned as a probe point gives physical access too, and none of those is a test_point part, so a net reached only that way reads as having no test point.

For hardware engineers ¶

A test point is the place a probe lands. During bring-up a scope or a meter clips on there, and in production a fixture’s spring pin (a bed of nails) or a flying probe makes contact there for in-circuit test. A net without one can still be reached at a component pin, but on a fine-pitch package or under a BGA there may be no pin anyone can touch.

So a review usually asks the negation, which nets have no test point at all, and then which of those matter: a rail, a reset line, a clock, the two ends of a part that in-circuit test should be able to measure. component.probed_both and component.probed_one build that last question out of this one.

For software engineers ¶

It is a semi-join. component.net pairs parts with the nets they sit on, component.class filters the parts to test points, and the head keeps only the net, so the answer is a set of nets with no duplicates however many test points share one.

The useful form is usually negated, not net.has_test_point(?n). A negated atom needs something else in the body to range over nets first. entity(?n, "net") is the complete list, so it finds nets that nothing else in the query would reach.

Datalog ¶

Every net with no test point:

entity(?n, "net"), not net.has_test_point(?n) => ?n

How many nets are covered, against how many there are:

net.has_test_point(?n) => count(?n)

How it is defined ¶

net.has_test_point(n: net), a derived relation in the net module, defined in Datalog in stdlib/lib/net.dl. In a clause, a bare name is another member of the same module and a dotted name is a full path.

has_test_point(?n: net) :- component.net(?tp, ?n), component.class(?tp, "test_point");

agni query --relations net.has_test_point prints the same definition. Adding a library member explains how the library is built.