Subject: RE: [sv-bc] Re: SV31A LRM interpretation for: unique case
From: Shalom.Bresticker@motorola.com
Date: Thu Feb 19 2004 - 04:27:43 PST
I still have some problems with the wording.
The LRM says,
"A unique case shall guarantee no overlapping case values".
(Read "items" for "values".)
This is incorrect. It does not "guarantee" anything.
It does not go and change the code I have typed in.
At most, it checks whether there are overlaps and warns me about it.
Second, the wording for "unique if" is,
"A software tool shall issue an error if it determines that more than one
condition is, or can be, true. A software tool shall also issue an error
if it determines that no condition is true, or it is possible that no
condition is true, and the final if does not have a corresponding else."
This wording implies that the check is a static one, performed at
compilation time, whereas the discussion in the last mails about
'unique case' talks about run-time errors.
Third, regarding "overlapping case items":
In the given example,
unique casex (value)
'b111x, `b11x1: $display( "case item 1 executed" ); //1st case item - has multiple true case expressions
'b1101: $display( "case item 2 executed" ); //2nd case item - has no true case expression
endcase
in actual fact, the case items DO overlap. 'b11x1 overlaps 'b1101.
'b11x1 is a superset of 'b1101. This has nothing to do with the whether or
not the value 'b1101 actually occurs during simulation. If you give this
to a lint tool, it WILL tell you that the case items overlap.
Finally, the LRM also says,
"If the case is qualified as priority or unique, the simulator shall issue
an error message if an unexpected case value is found."
The word "unexpected" is out-of-place.
The simulator has no idea what is expected or unexpected,
only whether values are specified or not, or fulfill one or more of the
case items or not.
An unspecified value can be expected, and a specified value can be
unexpected.
I suspect that after getting answers to these questions,
I will have further problems with the current or corrected language.
-- Shalom Bresticker Shalom.Bresticker@motorola.com Design & Reuse Methodology Tel: +972 9 9522268 Motorola Semiconductor Israel, Ltd. Fax: +972 9 9522890 POB 2208, Herzlia 46120, ISRAEL Cell: +972 50 441478[x]Motorola General Business Information [ ]Motorola Internal Use Only [ ]Motorola Confidential Proprietary
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