RE: [sv-bc] 19.12.5: array of instances connection to packed array port

Yes, it definitely makes sense.

Once such notion is defined, the bit mapping between the original type
and the vector will also be needed to be defined, in both directions.
This will help in understanding how the ports of arrays of instances are
mapped.

Note that there can be some complexities in such definition. For
example:

1. Mapping from the bit vector to the original type is ambiguous, when
the original type contains packed unions.

2. Note every slice of the vector can be mapped to a single slice of the
original type. For example, if we have two dimensional array
a[1:0][1:0], which is mapped into a one-dimensional vector a'[3:0], then
the slice a'[2:0] doesn't have direct representation using a single
slice on "a".

3. If the original type contains a packed struct with one member, should
the slice on the vector that slices the whole struct be mapped to the
member of the struct, or to the whole struct?

Still, it would be much better if the notion of the vector and the
definitions of the mapping are defined explicitly, rather than left to
the imagination of LRM readers and tool implementers.

--Yulik.

-----Original Message-----
From: owner-sv-bc@server.eda.org [mailto:owner-sv-bc@server.eda.org] On
Behalf Of Jonathan Bromley
Sent: Wednesday, September 20, 2006 1:05 PM
To: sv-bc@server.eda-stds.org
Subject: RE: [sv-bc] 19.12.5: array of instances connection to packed
array port

> I think the phrase could be made more successful if it were phrased in
> terms of bit significance, starting from LSB to MSB (indirectly
> referring to the vector equivalent Steven mentioned)

Would it not be better still if we had an explicit notion of the
"equivalent vector" of any packed object?  I suspect that would be
useful in other situations too.  By defining the equivalent vector
to have a normalized subscript range [N-1:0] you could make it
rather easy to rewrite 19.12.5.

I'm not suggesting that "equivalent vector" be defined in 19.12.5,
but rather that it be a definition quite early in the LRM that
can be used in discussion of *any* packed object.

Nor am I suggesting that the equivalent vector be required to
exist as a real physical object.  It would be only a convenient
(and well-defined) fiction in the LRM.
-- 
Jonathan Bromley, Consultant

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