Re: errata/486: 12.3.3: Implicit nets are not necessarily unsigned

From: Shalom Bresticker (Shalom.Bresticker@motorola.com)
Date: Tue Sep 23 2003 - 06:40:01 PDT

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    The following reply was made to PR errata/486; it has been noted by GNATS.

    From: Shalom Bresticker <Shalom.Bresticker@motorola.com>
    To: Steven Sharp <sharp@cadence.com>
    Cc: etf-bugs@boyd.com
    Subject: Re: errata/486: 12.3.3: Implicit nets are not necessarily unsigned
    Date: Tue, 23 Sep 2003 17:23:56 +0300

     The origin of this paragraph can be found in
     
     http://boydtechinc.com/btf/archive/btf_1998/0059.html and
     http://boydtechinc.com/btf/archive/btf_1998/0060.html
     
     I agree with your suggested change.
     
     I would also suggest adding a reference to 3.5 (implicit net declarations),
     and in the example following this paragraph, change the comments on
     "a" and "e" from
     "no explicit declaration" to
     "no explicit net declaration".
     
     Shalom
     
     
     Steven Sharp wrote:
     
    > >According to 12.3.3, "Implicit nets shall be considered unsigned.",
    > >but the comments in the example below it (and common sense) contradict
    > >that.
    >
    > >And I don't know what this sentence means --
    > >
    > > "Nets connected to ports without an explicit net declaration shall
    > > be considered unsigned, unless the port is declared as signed."
    >
    > Presumably it is talking about a net that was only declared as a port.
    > Of course, that is an implicit net, which it just said was always unsigned.
    >
    > My guess is that it is distinguishing the case of an implicit net that
    > is created by a port declaration without an explicit net declaration
    > (which gets the signedness of the port declaration), from an implicit
    > net that is created by use in an instance port expression or LHS of a
    > continuous assignment (which is always a scalar, and presumably unsigned).
    >
    > Note that the first case of implicit nets was not actually mentioned in
    > the 1995 standard, but was documented in the 2001 standard. Perhaps this
    > text in 12.3.3 was written before this was changed, so that the term
    > "implicit net" didn't include ports without explicit net declarations yet.
    >
    > Assuming this was the intent, I would suggest reversing these two sentences
    > and adding the word "other", as follows:
    >
    > "Nets connected to ports without an explicit net declaration shall be
    > considered unsigned, unless the port is declared as signed. Other implicit
    > nets shall be considered unsigned."
     
     --
     Shalom Bresticker Shalom.Bresticker@motorola.com
     Design & Reuse Methodology Tel: +972 9 9522268
     Motorola Semiconductor Israel, Ltd. Fax: +972 9 9522890
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