implicitnet_demo.va

// implicitnet_demo.va -- Enhancement-41: implicit nets in instance connections.
//
// Per the LRM's structural-connection semantics, a plain identifier used in a
// module-instance port connection that names nothing declared in the enclosing
// module is IMPLICITLY declared as a scalar net. In the Verilog-A subset the
// `default_discipline directive is excluded (AMS LRM appendix), so the implicit
// net's discipline is derived from the CONNECTED PORT instead -- exactly what
// discipline resolution produces for the common case of joining compatible
// ports. Two connections implying conflicting disciplines for the same implicit
// net are a hard error ("declare it explicitly").
//
// Before Enhancement-41 every internal wiring node had to be declared manually
// ("'mid' was not found in the current scope"). Implicit nets are synthesized in
// the module-instantiation elaboration pass (Enhancement-5): each one becomes a
// local net of the module its instantiation appears in -- so nested implicit
// nets are alpha-renamed per instance like every other local, and two flattened
// instances of the same submodule never accidentally share one net.
//
// Undeclared identifiers ANYWHERE ELSE (e.g. inside V()/I() access functions)
// remain errors: implicit declaration is a structural-connection mechanism only.

`include "disciplines.vams"

module r1k(p, n);
    inout p, n;
    electrical p, n;
    parameter real r = 1e3 from (0:inf);
    analog I(p, n) <+ V(p, n) / r;
endmodule

// submodule with its OWN implicit internal net `w` (two 1k in series = 2k)
module ser2k(p, n);
    inout p, n;
    electrical p, n;
    r1k a1(p, w);          // `w` implicit
    r1k a2(w, n);
endmodule

// top: implicit `mid` joins two ser2k instances (4k total). Each instance's
// internal `w` must remain DISTINCT after flattening -- a cross-instance short
// would halve the resistance.
module implicitnet_demo(in, out);
    inout in, out;
    electrical in, out;
    ser2k s1(in, mid);     // `mid` implicit (positional form)
    ser2k s2(.p(mid), .n(out));   // named form on the same implicit net
endmodule