RE: [sv-bc] 4.10.4 "Enumerated types in numerical expressions" - unclearness

Shalom,

I agree with you that this needs to be explicit defined and is not that
difficult to do so. Variables have initial state, and require a
definition for their default initial value. Nets have an un-driven state
when they are unconnected or driven with high impedance. The only
situation where the default initial state and un-driven state for a
given type would be different is when the type is 4-state.

The question is: what's the best way to clearly define this? Can it be
fully described in a single table? Or do need a description for each
type?

Dave


> -----Original Message-----
> From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On Behalf Of
> Bresticker, Shalom
> Sent: Saturday, November 05, 2005 10:53 PM
> To: Steven Sharp; sv-bc@eda.org
> Subject: RE: [sv-bc] 4.10.4 "Enumerated types in numerical
expressions" -
> unclearness
> 
> Hi,
> 
> See below.
> 
> >In SystemVerilog, there are too many types to make this
> >approach practical.
> >What was needed was a concise generic term for the value to be
> >used in these
> >situations.  Since the most obvious place where this value is
> >used is the
> >default initial value of a variable, the term "default initial
> >value" came
> >into use.  And as the standard was clarified and new situations
> >needing an
> >"undefined" value were identified, they were generally defined
> >to use this
> >"default initial value".
> 
> 
> [Shalom: ] The phrase "default initial value" is actually only used in
a
> small number of places:
> 
> - Here in 4.10.4.3 and 4.10.4.4, regarding enumeration next() and prev
> ()
> - In 4.11, p. 30, with respect to a variable of an unpacked union type
> - In 5.6.1, with respect to dynamic arrays
> - In 5.9.6, with respect to non-existent members of associative arrays
> - In 5.13, in a similar context
> - In 5.14.1, in a similar context with respect to queues
> - In Table 6-1 with respect to variables
> - In 19.12.1, with respect to variables
> 
> Thus the phrase used in 4.10.4.3 and 4.10.4.4 as it currently stands
is
> at best not well defined. The "default initial value" of an
> "enumeration" is not well defined. What is defined is the "default
> initial value" of an enumeration variable, which is not the same
thing.
> 
> 
> >When some of the new data types were allowed on nets, this
> >phrase became
> >less accurate.  It really should have become "default initial
> >value for
> >a variable of this type", but that is no longer concise and may
> >even be
> >more confusing.  Perhaps these places should have been changed
> >to say
> >"the value from Table 6-1".
> 
> [Shalom: ] I am not sure that in the case of enumerations, "the value
> from Table 6-1" would be unambiguous. For enumerations, Table 6-1
says,
> "base type default initial value". But that brings us back to the
> original question, as "default initial value" is defined for
variables,
> not for types.
> 
> You might have to say something like "default initial value for a
> variable of the base type".
> 
> Since Table 6-1 does not apply to nets, it might be wise to avoid
saying
> "default initial value" of a type, but rather "of a variable of this
> type", as you said, even though you have some reservations about it.
> 
> Thanks,
> Shalom
>