[sv-champions] Re: [sv-sc] some comments on mantis items

Hi Tom:

I recommend that the restriction be taken out.

For example, if I wanted to write in a checker

   covergroup cg_foo @(posedge my_checkvar)
      <blah blah blah>
   endgroup

   cg_foo foo = new();

then this restriction is making me recode it as
something like

   covergroup cg_foo;
      <blah blah blah>
   endgroup

   cg_foo foo = new();

   always @(posedge my_checkvar)
       foo.sample();

If there is a reason that the semantics of these examples 
should be illegal, then both need to be forbidden.

J.H.


> Date: Thu, 31 Jul 2008 10:46:21 -0700
> From: Thomas Thatcher <Thomas.Thatcher@Sun.COM>
> Sender: Thomas.Thatcher@Sun.COM
> Cc: sv-champions@eda.org, sv-sc@eda.org
> Reply-to: Thomas.Thatcher@Sun.COM
> X-OriginalArrivalTime: 31 Jul 2008 17:46:41.0621 (UTC) FILETIME=[63FA1850:01C8F335]
> 
> Hi John,
> 
> In my opinion, there is no real reason why a checker variable could not 
> be used as the covergroup sampling event.  This restriction was 
> requested by other committee members who wanted to prevent users from 
> doing things that might have non-intuitive results.
> 
> Normally, if a checker input signal is used as the sampling event, the 
> event occurs in the Active region.  If the covergroup is sampling 
> variables assigned by non-blocking assignments or variables which are 
> assigned from non-blocking assignments, then the covergroup samples the 
> old values of the variables.
> 
> At the time, the concern was that a sampling event using a checker 
> variable would occur in the Reactive region.  At this time, all 
> non-blocking assignments have completed, so the covergroup would then 
> sample the new values of the variables.
> 
> Now however, checker inputs are defined to be sampled, so this 
> restriction is no longer needed.  I can take it out of the proposal if 
> you like.
> 
> Tom
> 
> John Havlicek wrote:
> 
> > 
> > 3.  2088  SV-SC  Allow Checker construct (0001900) to include covergroups
> > 
> > I don't understand the rationale for the restriction that the covergroup
> > event cannot reference a checker variable.  Couldn't this effect be 
> > achieved by created code in the checker that is sensitive to the 
> > checker variable and then using an active triggering mechanism (e.g.,
> > "->cg_event")?  Perhaps there are more restrictions in other checker
> > proposals that forbid this kind of code.
> > 
> 

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