RE: [sv-ac] Re: Clock flow

Hi All,

I think: 
A) The status quo is most accurate/least troublesome. While I sympathize
with John's unclocked sequence scenario I think that case is better
handled by a default clock. To me, ended/matched are the same -- we must
remember that ended also "works" in multiple clock situations, like
matched, however it has the added restriction of checking whether clocks
are same and supposedly flags an error if not.

If we were to allow sneaking in the clock based on context for ended
even if just for unclocked sequences it breaks the consistency between
matched/ended even the meaning of them, allowing the context to
*implicitly* generate new sequence creatures worse if we add special
cases ... Not to mention this is a slippery slope of more special cases
... SO ...  

B) We can mimic this "extension" today I believe without changing
semantics while preserving consistency between ended/matched: Do
something like sequence(clk).ended/matched, right ?

Thx.
-Bassam.


--
Dr. Bassam Tabbara
Architect, R&D
Novas Software Inc.
(408) 467-7893

-----Original Message-----
From: owner-sv-ac@eda.org [mailto:owner-sv-ac@eda.org] On Behalf Of
Eduard Cerny
Sent: Wednesday, August 31, 2005 5:11 PM
To: john.havlicek@freescale.com; Manisha_Kulshrestha@mentor.com
Cc: sv-ac@eda.org
Subject: RE: [sv-ac] Re: Clock flow

I agree with you on both ended and matched.
ed
 

> -----Original Message-----
> From: owner-sv-ac@eda.org [mailto:owner-sv-ac@eda.org] On Behalf Of 
> John Havlicek
> Sent: Wednesday, August 31, 2005 7:27 PM
> To: Manisha_Kulshrestha@mentor.com
> Cc: john.havlicek@freescale.com; sv-ac@eda.org
> Subject: [sv-ac] Re: Clock flow
> 
> Hi Manisha:
> 
> > Is there any specific reason that the instance of a sequence with 
> > methods ended/matched are getting excluded in the above case ?=20
> 
> First, I believe that these restrictions can be relaxed without 
> introducing backward compatibility problems.  This is because saying 
> that the clock does not flow through ended/matched means the sequences

> instances to which these methods are applied must already have initial

> clocking events defined.  Thus, if the contextual clock flows in, it 
> will immediately be overridden by the internal clocks of the 
> sequences.
> 
> As I recall, the intuition for these restrictions was basically that a

> clock flowing into a sequence instance starts affecting the beginning 
> of that sequence, while ended/matched are references to the endpoints 
> of sequences.  Thus, there is something counterintuitive about have 
> the clock flow "backwards" to get to the start of the sequence 
> instance to which ended/matched is applied.
> 
> Also, "matched" involves synchronization between clocks, so I think 
> the committee preferred to avoid the clock flow in this case.
> 
> On the other hand, especially with "ended", I think the case can be 
> made that it is a nuisance to forbid the clock to flow in.
> 
> For example, if I want to code my sequences as unclocked and only 
> attach my clock at the top level of a property, then I want that clock

> to be able to flow to all parts of the property.  If I need to use 
> "ended", then I am stuck--I have to declare an explicit clock for each

> sequence to which I want to apply ended, and I have to make sure it 
> matches the clock in the context where ended appears.  This makes 
> those sequences less re-usable, or it forces me to a different coding 
> style in which the clock gets passed in as an argument.
> 
> My current opinion is that it would be a good thing to relax this 
> restriction for "ended", at least if "ended" is applied to an instance

> of an unclocked sequence.
> 
> In the case of matched, it is less clear to me that it is a good idea 
> to relax the restriction.
> 
> I am curious to hear other opinions on this topic.
> 
> Best regards,
> 
> John H.
> 
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> > From: "Kulshrestha, Manisha" <Manisha_Kulshrestha@mentor.com>
> > Cc: <sv-ac@eda.org>
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> > Hi John/All,
> > 
> > In section 17.12.3 (Clock Flow), P1800 draft, it says that:
> > 
> > The scope of a clocking event flows into an instance of a named 
> > property. The scope of a clocking event flows into an instance of a 
> > named sequence provided neither method ended nor method matched is 
> > applied to the instance of the sequence.
> > 
> > Is there any specific reason that the instance of a sequence with 
> > methods ended/matched are getting excluded in the above case ?=20
> > 
> > Thanks.
> > Manisha
> > 
>