Re: [sv-bc] A question about interfaces and modports

Subject: Re: [sv-bc] A question about interfaces and modports
From: Peter Flake (Peter.Flake@synopsys.com)
Date: Thu Oct 23 2003 - 08:57:52 PDT

Hi Dan,

My answers are below.

At 16:05 23/10/2003 +0200, Jacobi, Dan wrote:

The system Verilog LRM clearly specifies that if no modport is used in the model header or in the port connections then, all the nets and variables in the interface are accessible and will receive a direction of an inout or a ref (proposed to change to inputs). This enabled us to use interfaces with out declaring modports.

 

However me any my colleagues were debating the following issue:

 

Lets assume we have an interface and only part of it s variables and nets are members of a specific modport declared in this interface such as the following RTL:

 

            interface i1();

            reg r1,r2;

            wire w1,w2;

            modport master  (input r1,w1);

            modport slave     (output w1,r1, input r2,w2);

            endinterface : i1

 

Then we use that modport as a port in a declared module

            module top();

            i1 myint();

            son s1(myint);

            &

            endmodule

 

            module son (myint.master p1);

            &

            endmodule

 

 

The question is, are the variables and nets that were not declared as part of the modport accessible by the

module using that modport ? if they are what is the direction of these signals.


No

 

Or in a more high level aspect, is the modport used only to define a set of directions of the interface s signals when the interface is used as a modules port, or is the modport used to specify which signals should be connected to the module ?


Both. If you want to specify the signals but not the directions you can specify them as inout or ref.

 

Back to my RTL In the model son can we access the signals p1.r2 and p1.w2 ? If we can what are the corresponding directions ?

 

No


Should we add some language that clarifies this issue

 

Yes

Peter.

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