RE: [sv-ec] RE: [sv-bc] Hierarchical reference in clocking signal

Jonathan,

On the surface, it does look as if an interface port is just taking a
reference to an interface instance, and allowing it be used as the root
of a hierchical reference within the module.  The LRM even claims "The
syntax of interface_name.modport_name reference_name gives a local name
for a hierarchical reference." 

However, this viewpoint breaks down for modports.  The LRM also claims
"The keyword modport indicates that the directions are declared as if
inside the module." 

This was discussed in 

     http://www.eda-stds.org/sv-bc/hm/5602.html 

An 'output' qualifier on a variable in a modport is not just a synonym
for 'ref', because with an 'output' qualifier there is a continuous port
driver for the output variable components of a modport.

If 'output' were really just a synonym for 'ref' on a variable in a
modport, what purpose would that keyword serve there besides misleading
users who were expecting the "as-if" semantics of an 'output' port
declared inside a module? 

[ In reply to http://www.eda-stds.org/sv-ec/hm/4511.html .]

-- Brad

-----Original Message-----
From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of
Jonathan Bromley
Sent: Wednesday, July 11, 2007 11:45 AM
To: Arturo Salz; sv-bc@eda-stds.org; sv-ec@eda-stds.org
Subject: RE: [sv-ec] RE: [sv-bc] Hierarchical reference in clocking
signal

Arturo,

> I'm sorry if I mislead you. As we discussed in the past, we agreed to 
> remove the dotted expression forms from the clock-var

Don't apologize - I had totally forgotten about 594, which completely
deals with the issue.  Mea culpa, and thanks to Doug for highlighting
it.

> I was noting that not all dotted expressions represent hierarchical 
> expressions.

Clearly that's true, but I'm intrigued that you seem to be thinking of
the module/program's port of modport type as being something like a
struct variable.  I had always imagined it to be more like an alias for
the interface instance, with special visibility rules imposed by the
modport.  I need to go away and think harder about that - it has
significant impact on some stuff I've been exploring recently.

Thanks
--
Jonathan Bromley, Consultant

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