Re: [sv-ec] New Mantis on Coverage Calculation Corner Cases

I had a reaction to this one that I posted internally here at Mentor 
last week; I've been encouraged to post it to SV-EC ...


If I read Mark's suggestion right, I think that is saying that all-zero 
weights propagate as zero weight upward, i.e., all coverpoints/crosses 
weighted zero imply covergroup weight = 0. Is that right?

I'm worried about a couple of things.

One is that while this works out OK for the coverpoint/cross to 
covergroup level, presumably there is also weighting among covergroups 
to form the $get_coverage() value. So now you have to answer the 
question what $get_coverage() returns if all covergroup types are 
weighted 0. Mark's argument can't apply at this level, I don't think. 
I'm a little bothered by an algorithm not general enough to apply at all 
levels.

A more serious issue, I think, is this:

covergroup ct;
type_option.weight = 1;
coverpoint i { type_option.weight = 0; }
coverpoint j { type_option.weight = 0; }
endgroup
ct cv = new;

initial $display(ct::type_option.weight);

If I have interpreted Mark's suggestion correctly, this will have to 
display 0, in contradiction of the explicit assignment.

-- Dave Scott


Mark Strickland (mastrick) wrote:
> Doug/Arturo,
>
> I agree that negative weights are not needed and could be considered an
> error.  However, I'm not sure about zero coverage when all weights are
> zero.  I would like to be able to have two possibilities for a coverage
> point I did not want to participate in the overall coverage grade: I can
> still see its grade or I don't see it at all.  The weight of zero is how
> I would achieve the first.  If a group of coverage points who all have
> weight of zero show me a grade of zero, then I am prevented from seeing
> the actual achievement for that group.  The solution that allows me to
> see the grade for a group with all weights zero but does not affect the
> overall grade is to calculate the grade as if all the weights were one
> but then assign a weight of zero to the group grade.
>
> Mark
>
> -----Original Message-----
> From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of
> Arturo Salz
> Sent: Monday, October 30, 2006 2:45 PM
> To: Warmke, Doug; sv-ec@eda.org
> Subject: RE: [sv-ec] New Mantis on Coverage Calculation Corner Cases
>
> Doug,
>
> I added a bugnote expressing my opinion:
>
> 1) If the sum of all weights (Wi) is zero then the coverage (Cg) should
> yield zero.
>
> 2) A negative weight should be an error. Unsigned weights are likely to
> just generate garbage reports and force more work upon users.
>
> 	Arturo
>
> -----Original Message-----
> From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of
> Warmke, Doug
> Sent: Saturday, October 28, 2006 4:22 PM
> To: sv-ec@eda.org
> Subject: [sv-ec] New Mantis on Coverage Calculation Corner Cases
>
> Hi All,
>
> Some simple corner cases were identified in 18.10 on Coverage
> Calculations.  The first is if the sum of all weights Wi in the
> denominator of the Cg equation is 0.
> The second is what to do about negative weights.
>
> Can you please read
>   http://eda.org/svdb/bug_view_page.php?bug_id=0001655
> and express any opinions on the two corner cases?
>
> Thanks,
> Doug
>
>