RE: [sv-bc] RE: [sv-ec] Inconsistencies in virtual interfaces and modports

I would like to add support for Jonathan's suggestion that the standard be
more explicit that variables used in interfaces have a single source
semantic.  This has been my expectation all along, and I teach that rule in
my training courses.  Students, read "users", agree that this is an
important semantic restriction on the use of variables.  In fact, this very
topic came up in a class I was teaching today, and the student asking the
question wanted assurance that the use of variables in an interface would
enforce the single-source coding style required in their design work.

The same semantic restriction needs to be enforced when uwire is used in an
interface.

Stu
~~~~~~~~~~~~~~~~~~~~~~~~~
Stuart Sutherland
Sutherland HDL, Inc.
stuart@sutherland-hdl.com
503-692-0898
 

> -----Original Message-----
> From: owner-sv-bc@server.eda.org 
> [mailto:owner-sv-bc@server.eda.org] On Behalf Of Jonathan Bromley
> Sent: Wednesday, July 18, 2007 6:01 PM
> To: sv-ec@server.eda-stds.org; sv-bc@server.eda-stds.org
> Subject: [sv-bc] RE: [sv-ec] Inconsistencies in virtual 
> interfaces and modports
> 
> With (muted) apologies for following-up my own post...
> 
> > Recent discussion of the semantics of a modport element with
> > output direction has converged on the idea that modport output
> > to a variable in the interface represents a continuous 
> > assignment to the variable from something in the connected
> > module.  I'm fairly sure that most tools currently get 
> > this wrong
> 
> Of three major simulators:
> - One doesn't error on multiple explicit continuous assigns
>   to a variable - not even when both assigns are in the same
>   scope as the variable itself -  so it's no big surprise 
>   that it also doesn't error on multiple writes to a 
>   variable in an interface via "output" modports.
> - Two correctly report multiple explicit continuous assigns
>   to a variable, but do NOT report any error on multiple 
>   writes to an interface variable via "output" modports.
> 
> So there is *absolutely no* de-facto support for the consensus
> opinion I mentioned in the earlier post, but there is strong
> de-facto support for the "output === ref" position that I 
> mistakenly took earlier in the discussion.
> 
> Do I simply submit bug reports to three vendors, or do we need 
> some LRM clarification?
> -- 
> Jonathan Bromley, Consultant
> 
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