[sv-ac] RE: Call to vote: Due May 16

Hi Scott,

Please, see my comments below.

Thanks,
Dmitry

From: Little Scott-B11206 [mailto:B11206@freescale.com]
Sent: Monday, May 16, 2011 17:07
To: Korchemny, Dmitry; 'sv-ac@eda-stds.org'
Subject: RE: Call to vote: Due May 16

Mantis 3213 ____ Yes __X__ No

http://www.eda-stds.org/mantis/view.php?id=3213
http://www.eda-stds.org/mantis/file_download.php?file_id=5003&type=bug

-In the introductory explanation at the top of page 2 there is still a reference to $concurrent.
[Korchemny, Dmitry] Fixed.

-In 16.5.1 the final sentence in the second item in the section is very awkward. Could it be reworded as: “For example, the sampled value at time 0 of variable y of type logic is X.”?
[Korchemny, Dmitry] This was a typo. Fixed.

-In 16.5.1, the second bullet states, “The initial value of any other variable or net is the default value of the corresponding type…” Do you mean the initial sampled value?
[Korchemny, Dmitry] This bullet states: “A sampled value of a variable in a time slot corresponding to time 0 is the initial value of this variable.” Then it explains what the initial value of a variable is. This text was moved from 16.9.3 Sampled value functions here.
Then farther down in the enumerated list you state that the initial sampled value of an automatic or local variable is undefined. I believe the second statement is what you want, but I believe the first statement should be clarified. What are the implications of making initial sampled values undefined? Is it a simulator error if an assertion needs a sampled value of an automatic variable in the initial timestep? This feels to me like it is working against the basic principles of the proposal to allow a more free use of “nonstandard” variables throughout the assertions. Why not take the default type values instead of undefined?
[Korchemny, Dmitry] My definition should be correct. The initial sampled values are used only in sampled value functions where all these undefined cases are forbidden, so there is no need to specify their behavior in simulation. However, to simplify the proposal I followed your suggestion and modifies these bullets as follows:

¾ An initial sampled value of a variable is its initial value, explicit or implicit, (see 6.8).

¾ An initial sampled value of sequence methods triggered and matched is 1’b0.

¾ An initial sampled value of an expression is defined recursively using values of its arguments.

[Note: Ed seems to be concerned about this point as well. I am not sure it is adequately addressed at this point although I don’t have any particularly good ideas about how to improve the situation.] I understand why it is done, but I think the descriptions of the sampled value functions have become somewhat confusing for the common case (static variables). “$past returns the sampled value of expression1 from the Postponed region of a particular time step strictly prior to the one in which $past is evaluated.” For static variables the sampled value doesn’t change in a timestep, so where the sampled value is grabbed doesn’t matter. I am not sure that is obvious to the casual reader. In fact, I wonder if folks may misinterpret this to mean that variables are sampled in the Postponed region instead of that the sampled value is captured in the Postponed region. I would like to see the definition of the common case more clearly stated, but I am afraid this may clutter up the definitions.

[Korchemny, Dmitry] I share Ed’s and your concerns, and I added an additional explanation at the beginning of 16.9.3 in one of the recent versions of my proposals. I will appreciate if you or other people can suggest a better language for it.

Mantis 3385 __X__ Yes ____ No

http://www.eda-stds.org/mantis/view.php?id=3385
http://www.eda-stds.org/mantis/file_download.php?file_id=4999&type=bug

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