[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.