From: Steven Sharp (sharp@cadence.com)
Date: Mon Aug 12 2002 - 15:50:02 PDT
Precedence: bulk
The following reply was made to PR errata/84; it has been noted by GNATS.
From: Steven Sharp <sharp@cadence.com>
To: etf-bugs@boyd.com, Shalom.Bresticker@motorola.com
Cc:
Subject: Re: errata/84: Should @* include delay controls?
Date: Mon, 12 Aug 2002 18:43:54 -0400 (EDT)
> But, regarding the "iterative vector indexing implicit sensitivity," at least
in
> the example you give, isn't that a case where i is a temporary variable
assigned
> before its use, where we say that it will not be included in the sensitivity
> list?
There is no such exception in the standard. I don't know whether there was
an attempt to put in such an exception at some point. I don't see a good way
to add such an exception. In the general case, I believe that the question
of whether a variable is guaranteed to be assigned before being used can be
reduced to the halting problem, and is therefore uncomputable.
> I claim that we must not, if at all possible, deliberately create a situation
> where a legitimate way of writing combinational logic will simulate wrong
using
> @*.
I completely agree.
> Regarding arrays, it would be possible to say it should map to mem[addr] in
> Mac's example. In cases where that might not be sufficient, the standard could
> say that @* does not cover that case and implementations might give an error
> message if they cannot map it correctly.
>
> I also agree with the approach that it is better to give a mapping that might
be
> overkill but works, rather than something which is efficient but wrong. The
> latter is out of the question in my mind.
And I agree that if an implementation can find a way of handling some or all
memory references in a way that always gives the desired results, that it
would be nice to allow it. But it should give an error rather than do it
wrong.
Steven Sharp
sharp@cadence.com
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