[sv-ec] RE: [sv-bc] Interface ports and hierarchical referencing

The particular example you have given below has to be illegal, because
the override of the parameter 'T' is the parameter 'T' itself and 'T'
has no default value.

I see no reason to restrict interface port actuals more just because you
can create loops in parameter overrides by misusing hierarchical
references in the actuals. There are already many other ways of creating
loops in parameter/type resolution. In test benches it is useful to use
hierarchical references to interfaces in interface port actuals.

-----Original Message-----
From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On Behalf Of
Gordon Vreugdenhil
Sent: Tuesday, January 08, 2008 8:24 AM
To: SV_EC List; SV_BC List
Subject: [sv-bc] Interface ports and hierarchical referencing


The current LRM doesn't place any restrictions on the actuals for
interface ports in an instantiation.  I think that there has been an
implicit assumption that interface flow is "downwards", but that has
never been explicitly stated in the LRM.

Consider the following:

    interface intf_def #(parameter type T);
    endinterface

    module top;
       child c(c.intf);
    endmodule

    module child(intf_def intf_inp);
       typedef intf_inp.T T;
       intf_def #(T) intf();
    endmodule


I don't think there is anything in the LRM that I can appeal to in
saying that this is illegal.

In general, how tight does everyone think the restrictions need to be?
Should an interface port actual be required to be a simple name (meaning
that it is either declared in a visible scope or is itself an interface
port)?

At a minimum, due to the type issues, when used as an interface port
actual, I don't think you should be able to reference anything below the
reference point.  In addition, there would likely need to be
restrictions regarding references through generates and array instances
as well.

Gord
--
--------------------------------------------------------------------
Gordon Vreugdenhil                                503-685-0808
Model Technology (Mentor Graphics)                gordonv@model.com


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