RE: [sv-ac] Samppled value functions

Hi John,

the change in the text is in 1737.
ed
 

> -----Original Message-----
> From: owner-sv-ac@eda.org [mailto:owner-sv-ac@eda.org] On 
> Behalf Of John Havlicek
> Sent: Tuesday, May 29, 2007 10:47 AM
> To: dmitry.korchemny@intel.com
> Cc: sv-ac@eda-stds.org
> Subject: Re: [sv-ac] Samppled value functions
> 
> Hi Dmitry:
> 
> Here is what I think the definition ought to be.
> 
> $rose, $fell, $stable compare the current timestep preponed 
> value of their first argument expression to another value.
> 
> This other value is supposed to be the preponed value of 
> the first argument expression at the nearest strictly prior
> timestep in which the clocking event occurred.  
> 
> However, if there is no such strictly prior timestep in which 
> the clocking event occurred, then I think the other value 
> should be the default initial value of the first argument expression,
> rather than just X.
> 
> I actually thought we had changed this already, but maybe it is
> in a proposal that has not yet been passed.
> 
> Do you agree?
> 
> Once we agree on a precise definition, Annex F needs to be 
> rewritten to conform to it.
> 
> J.H.
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> > From: "Korchemny, Dmitry" <dmitry.korchemny@intel.com>
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> > Hi all,
> > 
> > =20
> > 
> > There is some inconsistency between the LRM body and the formal
> > semantics. According to LRM (clause 16.8.3):
> > 
> > =20
> > 
> > A value change function detects the change in the sampled 
> value of an
> > expression. The clocking event is
> > 
> > used to obtain the sampled value of the argument expression 
> at a clock
> > tick prior to the current simulation
> > 
> > time unit. Here, the current simulation time unit refers to the
> > simulation time unit in which the function is
> > 
> > evaluated. This sampled value is compared against the value of the
> > expression determined at the Preponed
> > 
> > time of the current simulation time unit. The result of a 
> value change
> > expression is true or false and can be
> > 
> > used as a boolean expression.
> > 
> > - $rose returns true if the LSB of the expression changed to 1.
> > Otherwise, it returns false.
> > 
> > - $fell returns true if the LSB of the expression changed to 0.
> > Otherwise, it returns false.
> > 
> > - $stable returns true if the value of the expression did 
> not change.
> > Otherwise, it returns false.
> > 
> > When these functions are called at or before the first 
> clock tick of the
> > clocking event, the results are computed
> > 
> > by comparing the current sampled value of the expression to X.
> > 
> > =20
> > 
> > while according to the formal semantics (annex F.4), all 
> these functions
> > return false when called before the first tick of the 
> clocking event.
> > 
> > =20
> > 
> > Thanks,
> > 
> > Dmitry
> > 
> > 
> 
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