RE: [sv-bc] Assignment operator in continuous assignment

There is a difference in the way that a continuous assignment may be
scheduled.

The procedural 'always @b b = b + 1;' is really two procedural
statements: wait for an event on b, then increment b.

The continuous assignment 'assign b = b + 1;' says whenever there is an
event in an operand on the RHS, evaluate the RHS, which could leaded to
a zero-delay oscillation.

On the other hand, 'assign out = enable ? in : out ;' is OK because this
combinatorial loop will settle out.

Dave



> -----Original Message-----
> From: Bresticker, Shalom [mailto:shalom.bresticker@intel.com]
> Sent: Wednesday, October 10, 2007 1:02 AM
> To: Rich, Dave; Surya Pratik Saha; sv-bc@server.eda.org; sv-
> ec@server.eda.org
> Subject: RE: [sv-bc] Assignment operator in continuous assignment
> 
> It would have no effect.
> 
> It would be like writing
> 
> always @(b)
> 	b = b + 1;
> 
> That in itself would not be very useful.
> But one could write
> 
> assign b += c ;
> 
> which would be like
> 
> always @(b,c)
> 	b = b + c ;
> 
> which would trigger if c changed.
> 
> Many years ago, we used to sometimes write latches as
> 
> assign out = enable ? in : out ;
> 
> But I don't think it is useful enough to recommend allowing it.
> 
> Shalom
> 
> > -----Original Message-----
> > From: owner-sv-bc@server.eda.org
> > [mailto:owner-sv-bc@server.eda.org] On Behalf Of Rich, Dave
> > Sent: Wednesday, October 10, 2007 9:45 AM
> > To: Surya Pratik Saha; sv-bc@server.eda.org; sv-ec@server.eda.org
> > Subject: RE: [sv-bc] Assignment operator in continuous assignment
> >
> > This is specifically disallowed. What would it mean in terms
> > of sensitivity to have the same variable on both sides of '='?
> >
> > Dave
> >
> >
> > > -----Original Message-----
> > > From: owner-sv-bc@server.eda.org
[mailto:owner-sv-bc@server.eda.org]
> > On
> > > Behalf Of Surya Pratik Saha
> > > Sent: Wednesday, October 10, 2007 12:17 AM
> > > To: sv-bc@server.eda.org; sv-ec@server.eda.org
> > > Subject: [sv-bc] Assignment operator in continuous assignment
> > >
> > > Hi,
> > > In SV 1800, continuous assignment syntax allows only '='
assignment
> > > operator. Why '+=', '-=' types of assignment operator not
> > allowed. Why
> > > someone can't write:
> > >
> > > assign b += 1;
> > >
> > > Which is just similar to
> > > assign b = b + 1;
> > >
> > > Is there any specific reason or is it case of BNF overlook?
> > >
> > > --
> > > Regards
> > > Surya
> > >
> > >
> > >
> > >
> > >
> > >
> > > --
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