RE: [sv-ec] implicit sensitivity list and class dynamic members

The LRM is even less explicit about continuous assignments.

This is discussed in bugnote 2048 of Mantis 1013.

Shalom
 

> -----Original Message-----
> From: owner-sv-ec@server.eda.org 
> [mailto:owner-sv-ec@server.eda.org] On Behalf Of Rich, Dave
> Sent: Saturday, July 25, 2009 7:58 AM
> To: stuart@sutherland-hdl.com; Mark Hartoog; Vreugdenhil, Gordon
> Cc: Daniel Mlynek; sv-ec@server.eda.org
> Subject: RE: [sv-ec] implicit sensitivity list and class 
> dynamic members
> 
> The LRM says this about explicit events
> 
> Changing the value of object data members, aggregate elements, or the
> size of a dynamically sized array referenced by a method or function
> shall cause the event expression to be reevaluated. An implementation
> can cause the event expression to be reevaluated when 
> changing the value
> or size even if the members are not referenced by the method or
> function.
> 
> 
> Repeating Gordon's comment, it says nothing about implicit events.
> 
> Dave
> 
> 
> > -----Original Message-----
> > From: owner-sv-ec@server.eda.org [mailto:owner-sv-ec@server.eda.org]
> On
> > Behalf Of Stuart Sutherland
> > Sent: Friday, July 24, 2009 1:03 PM
> > To: 'Mark Hartoog'; Vreugdenhil, Gordon
> > Cc: 'Daniel Mlynek'; sv-ec@server.eda.org
> > Subject: RE: [sv-ec] implicit sensitivity list and class dynamic
> members
> > 
> > What about continuous assignments?  Will the assignment update on a
> call to
> > a method function.  For example (not in full context):
> > 
> > mailbox foo = new;
> > assign empty == (foo.num() == 0);
> >
> > Stu
> > ~~~~~~~~~~~~~~
> > Stuart Sutherland
> > stuart@sutherland-hdl.com
> > (503) 692-0898
> > 
> > 
> > > -----Original Message-----
> > > From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On 
> Behalf Of
> Mark
> > > Hartoog
> > > Sent: Friday, July 24, 2009 11:25 AM
> > > To: Gordon Vreugdenhil; Mark Hartoog
> > > Cc: Daniel Mlynek; sv-ec@eda.org
> > > Subject: RE: [sv-ec] implicit sensitivity list and class dynamic
> members
> > >
> > > I agree with you.
> > >
> > > Daniel's question was "Should such references be added to implicit
> > > sensitivity list?"
> > >
> > > I was just pointing out that if Daniel was asking if the 
> LRM should
> be
> > > changed to allow this, there are some problems with doing it.
> > >
> > > -----Original Message-----
> > > From: Gordon Vreugdenhil [mailto:gordonv@model.com]
> > > Sent: Friday, July 24, 2009 11:21 AM
> > > To: Mark Hartoog
> > > Cc: Daniel Mlynek; sv-ec@eda.org
> > > Subject: Re: [sv-ec] implicit sensitivity list and class dynamic
> members
> > >
> > >
> > > Mark,
> > >
> > > always_comb addresses the class method side directly in the text I
> > > quoted so I don't think virtual comes into play -- you 
> don't impact
> > > the sensitivity list with a virtual method call either.
> > >
> > > I view the "write rule" for always_comb as being tied to the
> > > sensitivity lists -- if we ignore methods and class objects for
> > > sensitivity, I think they should also be ignored for the
> > > "write rule".
> > >
> > > Gord.
> > >
> > >
> > >
> > > Mark Hartoog wrote:
> > > > I agree with Gord's interpretation that class objects, class
> methods and
> > > class properties do not add to the sensitivity list of always_comb
> or
> > @(*).
> > > >
> > > > If Daniel's question is should the LRM be changed to allow this,
> there
> > are
> > > a number of issues to consider.
> > > >
> > > > Always_comb sensitivity lists include sensitivities 
> from functions
> > called
> > > from the always_comb. Since class methods can be virtual, there is
> no way
> > to
> > > do this for virtual class methods.
> > > >
> > > > Always_comb also says it is an error for multiple always_comb to
> write
> > to
> > > the same variable. The aliasing problem with class 
> handles makes it
> very
> > > difficult to do this check for class fields.
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf
> Of
> > Gordon
> > > Vreugdenhil
> > > > Sent: Friday, July 24, 2009 6:49 AM
> > > > To: Daniel Mlynek
> > > > Cc: sv-ec@eda.org
> > > > Subject: Re: [sv-ec] implicit sensitivity list and class dynamic
> members
> > > >
> > > > Daniel,
> > > >
> > > > 9.2.2.2.1 explicitly deals with always_comb:
> > > >     References to class objects and method calls of 
> class objects
> do
> > > >     not add anything to the sensitivity list of an always_comb.
> > > >
> > > > 9.2.2.2.2 (on @(*)) is less clear although it claims that
> > > >     The SystemVerilog always_comb procedure differs from
> > > >     always @* (see 9.4.2.2) in the following ways:
> > > >        ...
> > > >
> > > > Whether @(*) is sensitive to class refs was never explicitly
> > > > addressed in the LRM, but it would be reasonable to interpret
> > > > the lack of comment about classes in 9.2.2.2.2 to imply that
> > > > @(*) should be sensitized to class references either.
> > > >
> > > > Gord.
> > > >
> > > > Daniel Mlynek wrote:
> > > >> I've a question related to implicit sensitivity list (@*,
> always_comb).
> > > >> This feature was assumed to help users in design code - for
> > > >> combinatorial blocks. But in blocks under @* or 
> always_comb also
> > > >> references to dynamic class members can be used - as in below
> code.
> > > >> Should such references be added to implicit sensitivity list>
> > > >>
> > > >>     class class0;
> > > >>      int x;
> > > >>     endclass
> > > >>
> > > >>     module top_006;
> > > >>      class0 c0 = new;
> > > >>      class0 c1 = new;
> > > >>
> > > >>      initial begin
> > > >>         #10 c0.x = 1;
> > > >>         #10 c0.x = 0;
> > > >>         #10 c0.x = 1;
> > > >>         #10 c0 = c1;
> > > >>      end
> > > >>      always@* $display($time, c0.x);        //should this be
> sensitive
> > > >>     to c0.x?
> > > >>     endmodule
> > > >>
> > > >> DANiel
> > > >>
> > > >> --
> > > >> This message has been scanned for viruses and
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> > > >
> > > > --
> > > >
> --------------------------------------------------------------------
> > > > Gordon Vreugdenhil                                503-685-0808
> > > > Model Technology (Mentor Graphics)
> gordonv@model.com
> > > >
> > > >
> > > > --
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> > > --
> > > 
> --------------------------------------------------------------------
> > > Gordon Vreugdenhil                                503-685-0808
> > > Model Technology (Mentor Graphics)                
> gordonv@model.com
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Intel Israel (74) Limited

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