RE: [sv-ec] virtual interfaces restriction

I believe the restriction is the same as what's written in 6.21,
"References to automatic variables and elements or members of dynamic
variables shall be limited to procedural contexts."

 

The text mentioned in mantis 1441 is really referring to implicitly
generated sensitivity lists created in non-procedural contexts. All it
really need to say is "limited to procedural contexts"

 

always @(vi,a) $display(vi.a);

 

is equivalent to 

 

always begin

            @(vi.a);

            $display(vi.a);

            end

 

And both are currently legal.

 

What's not currently legal is

 

always_comb $display(vi.a);

assign X - vi.a

 

The reason for the restriction is purely one of caution on the part of
the SV-EC committee members at the time. They did not want to open up
the functionality until gaining some experience with dynamic variables.
I have seen the desire to connect class members to ports or continuous
assignments and have been frustrated by this restriction.

 

A plausible case for relaxing this restriction is where the dynamic
variable is statically initialized as a const and null handle reference
are unlikely.

 

Dave

 

 

 

________________________________

From: owner-sv-ec@server.eda.org [mailto:owner-sv-ec@server.eda.org] On
Behalf Of Daniel Mlynek
Sent: Thursday, January 15, 2009 6:11 AM
To: sv-ec@server.eda.org
Subject: [sv-ec] virtual interfaces restriction

 

Mantis 1441 complatins that sensivity list in virtaul interface usage
restriction is not well defined.

http://www.verilog.org/mantis/view.php?id=1441
<http://www.verilog.org/mantis/view.php?id=1441> 

That is true that sensivity list should be defined.

 

But imho there is no sense for forbiding virtual interfaces on sensivity
list as this is hard to define. The 2nd restriction about assign is ok -
as vi was not added for design construct and assign is purely design
one.

Summarizing I do not see the reason to forbid the code:

 

module top;
        iface if1();
        iface if2();
        virtual iface vi=if1;

 

        always @(vi.a) begin //vi on sensivity list
                $display($time);
        end

 

        initial
                forever @(vi.a) 
                $display("2 %d",$time);

endmodule

 


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