RE: [sv-bc] Mantis 1345: 10.4: "illegal" unique if/case issues

Oops, I just noticed that Steven also intended to forbid side-effects in
case item expressions. Anyway, the approach I suggested is still
possible.

Shalom

> -----Original Message-----
> From: Bresticker, Shalom
> Sent: Friday, February 24, 2006 9:13 AM
> To: 'sharp@cadence.com'
> Cc: sv-bc@eda.org
> Subject: RE: [sv-bc] Mantis 1345: 10.4: "illegal" unique
> if/case issues
> 
> I haven't yet studied Greg's mail in detail, but 2 short
> comments:
> 
> 1. "How often does someone use a variable in a case item
> expression"?
> 
> Answer: Frequently. A common coding style is
> 
> case(1'b1)
> a: ...
> b: ...
> c: ...
> ...
> endcase
> 
> Frequently used with parallel_case directive.
> 
> 
> 2. Regarding side-effects, I was thinking along the same lines
> as Steven, I think. Define unique assuming no side-effects
> exist. State explicitly something like, "If side-effects exist,
> results may be indeterminate."
> 
> Shalom
> 
> 
> > -----Original Message-----
> > From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On
> > Behalf Of Steven Sharp
> > Sent: Friday, February 24, 2006 3:49 AM
> > To: sharp@cadence.com; Greg.Jaxon@synopsys.com
> > Cc: sv-bc@eda.org
> > Subject: Re: [sv-bc] Mantis 1345: 10.4: "illegal" unique
> > if/case issues
> >
> >
> > >From: Greg Jaxon <Greg.Jaxon@synopsys.com>
> >
> > >Brad has often
> > >suggested that SV prohibit side-effects here altogether,
> which
> > would
> > >probably not be practical for testbench uses;
> >
> > Can you give an example?  I think we can allow side-effects
> in
> > the
> > case expression, just not in the case item expressions.
> Since
> > >99%
> > of the time these are constants anyway, I don't see how this
> is
> > impractical.  How often does someone use a variable in a case
> > item
> > expression, much less something that could have a side
> effect,
> > like
> > an increment or assignment operator or impure function call?
> >
> > They certainly don't belong in anything synthesizable.  And
> > since
> > my understanding was that unique case was intended for
> > synthesis,
> > I don't think we should be worrying too much about them in
> > testbenches anyway.  Let's keep in mind what they are
> intended
> > for, instead of just focusing on the construct itself.