Subject: Clarification on sensitivity list
From: Craig Winters (cwinters@cadence.com)
Date: Wed Jan 09 2002 - 15:20:08 PST
Request for clarification of IEEE Std 1076.1-1999, (VHDL-AMS)
Working Group,
My question concerns the sensitivity list as described in section
8.1. This is used in the wait statement, process statement and
concurrent break statement. I believe it is the same construct
in each of these locations.
In section 8.1 is the statement:
Each signal name in the sensitivity list must be a static signal name.
To determine what is a static name, I refer to section 6.1 where
this text is found:
A name is said to be a static name if and only if one of the following
conditions holds:
- The name is a simple name or selected name [...]
- The name is an indexed name [...]
- The name is a slice name [...]
This does not seem to allow an attribute name where a static name is
required, as in the sensitivity clause. In that case, the following
would be errors:
WAIT ON q'ABOVE(e);
BREAK ON s'DELAYED(t);
However, example code in 14.1 for Q'SLEW contains such statements.
Specifically, the equivalent block contains two occurrences of:
WAIT ON q'ABOVE(qslew);
One possibility is that when the LRM uses "equivalent code" the
code is not necessarily substitutable for the construct being
defined, but only to explain to the reader what the specified
behavior is. (Please clarify this point.)
The other possibility it that, at least in the sensitivity list
some attribute names are permissible. If this is so then a number
of questions come to mind:
Can attribute names with static prefixes be considered static names?
Are certain non-static names, specifically, implicit signals, allowed
in the sensitivity list?
If attribute names which are implicit signal references can
be considered static names, does that include the case of
Q'ABOVE(E) where the expression E is non-static?
Finally, to get directly to my present issue, can a sensitivity
list, by any interpretation, contain a Q'ABOVE(E) expression where
the expression E is non-static?
Thank you for your help on this,
Craig Winters
Cadence Design Systems
cwinters@cadence.com
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