RE: [vhdl-200x] Minutes for VHDL-200X-FT meeting, San Jose Dec 4, 2003


Subject: RE: [vhdl-200x] Minutes for VHDL-200X-FT meeting, San Jose Dec 4, 2003
From: Guyler, Andrew (andrew_guyler@mentorg.com)
Date: Tue Dec 09 2003 - 09:11:49 PST


I have to agree with Andy...
 
"I would definitely NOT deprecate the use of "when" in conditional
signal assignments, since deprecation is usually applied only to
seldomly used language features, which is certainly not the situation
here. For deprecation to have any meaning, it would eventually lead to
removal from the standard, which would break untold thousands of lines
of legacy code."
  
    Andrew Guyler
    Mentor Graphics

-----Original Message-----
From: owner-vhdl-200x@eda.org [mailto:owner-vhdl-200x@eda.org]On Behalf
Of Andy D Jones
Sent: Tuesday, December 09, 2003 6:50 AM
To: VhdlCohen@aol.com
Cc: Jim@synthworks.com; vhdl-200x@eda.org
Subject: Re: [vhdl-200x] Minutes for VHDL-200X-FT meeting, San Jose Dec
4, 2003

[I subscribe to this list, but have not been able to post to it in the
past, so if it this does not make it onto the list, if one of you kind
Gentlemen would forward it, I'd appreciate it.]

WRT adding "if else" to conditional signal assignments, and possibly
deprecating "when else":

I prefer the use of "when" in concurrent assignment statements, since it
confers the context of the assignment as "whenever". Whereas "if"
confers an immediate condition that must exist at a certain time. The
actual enforcement of these meanings is performed by the (virtual)
processes surrounding each, but they remain a helpful reminder to the
reader.

If conditional assignments were allowed in sequential assignment
statements (which I do support), I would prefer that they use "if" in
those cases, to preserve the "whenever" nature of "when" in concurrent
assignments. I realize that "when" is also used in sequential case
statements without meaning "whenever", but that's a legacy of Ada and
other lanquages that do not have a concurrent statement context.

The use of "when" in concurrent conditional signal assignments is a
commonly used feature, and changing it now would be very confusing to
the majority of users. While I agree that the use of "when" is often
confused with selected signal assignments, this has been the case for
too long to change now. It has become "just one of those things you
have to know" about VHDL.

I would definitely NOT deprecate the use of "when" in conditional signal
assignments, since deprecation is usually applied only to seldomly used
language features, which is certainly not the situation here. For
deprecation to have any meaning, it would eventually lead to removal
from the standard, which would break untold thousands of lines of legacy
code.

Furthermore, in the absence of deprecating the use of "when" in
conditional assignment statements, I cannot support the addition of "one
more way" to code the same thing that is not substantially more
efficient, and does not confer substantially different context.

Andy D Jones
Lockheed Martin
Missiles & Fire Control
Dallas TX
andy.d.jones@lmco.com

VhdlCohen@aol.com wrote:

snip...

--------------------------------------------------
Add "if else" for conditional signal (deprecate when else?)
AReg <= A if rising_edge(Clk)
Ben: No objections.
--------------------------------------------------

snip....



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