[sv-ac] RE: Discussion of 2804 (inferring clocking event within procedure)

Hi, Erik.

As I remember, the original objective was to support the basic synthesizable subset for RTL. Anything that would be supported beyond that would be nice to have, but not essential.

The basic form has an event control with one or more event expressions, one of which is a clock, and the others are asynchronous resets.

There are extensions to that, but they are not in the minimum synthesizable subset.

Then the question was how to distinguish between the clock and the resets.

And all of this had to be done without mentioning the word "synthesis".

Disallowing the clock to be used in an expression was a way to distinguish a clock from an asynchronous reset.

There may also have been a desire to restrict the clock inference so as to get it working for the minimum synthesizable subset, but wait till a future revision with more flexible rules that might require deeper analysis.

Regards,
Shalom

> -----Original Message-----
> From: owner-sv-ac@eda.org [mailto:owner-sv-ac@eda.org] On Behalf Of
> Seligman, Erik
> Sent: Wednesday, December 29, 2010 12:36 AM
> To: Little Scott-B11206
> Cc: Korchemny, Dmitry; sv-ac@eda.org; Francoise Martinolle
> Subject: [sv-ac] RE: Discussion of 2804 (inferring clocking event
> within procedure)
>
> Hi Scott--
> I had assumed the previous restrictions were due to the difficulty of
> correctly inferring the clock when complex expressions are allowed, or
> when expressions in the always statement also appear in the body.
> Since we couldn't be sure what the user intended, it's best not to
> infer a clock. If this is the correct rationale, then in cases where
> the new rule provides a clear answer, we should be OK.
>
> If, on the other hand, the previous restriction was due to some
> implementation challenge of using a complex event expression to clock a
> procedure, or of using a procedure clock subexpression in the body, we
> need to revisit this.
>
> Does anyone recall the reasoning behind the original rules disallowing
> a complex event expression to be used as a procedure clock, and
> disallowing the clock to be used in an expression?

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