RE: [sv-ac] mantis 1550

I think the semantics of the return value of these function is no
different then the simple Verilog system function $time. 

You have to distinguish between the values returned by references to the
function versus evaluation events scheduled by a processes waiting on
the event expression. This is somewhat harder to put into words than to
actually implement it.

I think it is OK to say that the value that will be returned by the
function is updated in the postponed region because no one can schedule
a call in that region. You can also say that an update event is
scheduled for the active region of the next time slot.

Dave


> -----Original Message-----
> From: owner-sv-ac@server.eda.org [mailto:owner-sv-ac@server.eda.org]
On
> Behalf Of John Havlicek
> Sent: Thursday, November 02, 2006 6:59 AM
> To: sv-ac@server.eda-stds.org
> Subject: [sv-ac] mantis 1550
> 
> Hi Ed:
> 
> In general, I like the semantics for $sampled and $past in your 1550
> proposal, but I have some concerns that make me vote "no" at this
> time.
> 
> 1. I don't think we have yet clarified when the return values of these
>    functions change.  You say that $sampled is stable throughout the
>    simulator timestep and that $past changes in the postponed region.
> 
>    Can the return value of $past really change in the postponed
region?
> 
>    I think it is bad if there can be calls/references to any of the
>    sampled value functions between the point that the return value
>    of one changes and the point that the return value of another
>    changes in the same timestep.
> 
> 2. A related question is that of the semantics of events that refer
>    to sampled value functions.  The intuition seems to be that the
>    return values of sampled value functions change "in between" the
>    simulation timesteps, so when do we schedule something like
> 
>       @($sampled(p)) S1
> 
>    when written in various contexts (e.g., in a module, in a program)?
> 
> 
> 3. I would like to see $rose, $fell, and $stable defined in terms of
>    $sampled and $past.  I think this should be easy.
> 
> We may need to get some SV-BC or other help with items 1 and 2.
> 
> Best regards,
> 
> John H.