Why isnt buffer used more often?

Mon Dec 05, 2011 10:44 am   

Is there any reason more people dont use the buffer port type? is
there anything you cant do with it that you can do with an internal
signal?

Is it just an old thing that old synthesisors wouldnt support it, and
it has fallen out of favour?

Mon Dec 05, 2011 10:44 am   

Probably because it could mess up the design flow understanding.

Mon Dec 05, 2011 12:17 pm   

On Mon, 05 Dec 2011 10:54:33 +0200, scrts wrote:


I don't see how, really.

It could certainly mess up the process of verifying the design, mostly
because synthesis tools would pour out thousands of spurious warnings,
presumably hangovers from a much earlier release that might have got it
wrong. (For the record I never did see an actual problem, at least as far
back as Leonardo/Galileo, but there may have been some)

There were some (to my eyes, apparently unnecessary) rules about
connecting internal Buffer ports to higher level Out ports or vice-versa,
that made it difficult to mix the two styles, so Buffer was not as useful
in practice as it looked.

- Brian

Mon Dec 05, 2011 12:33 pm   

On 05/12/2011 08:44, Tricky wrote:

With the VHDL2008 capability of reading an output port I guess it will
become obsolete?

Hans
www.ht-lab.com

Mon Dec 05, 2011 6:29 pm   

On Dec 5, 5:33 am, HT-Lab <han...@htminuslab.com> wrote:

Depends on whether reading an output in 2008 version returns the
driven value or the resolved value of the output.

Andy

Mon Dec 05, 2011 10:58 pm   

Buffer ports worked fine last time I tried it.
As I recall, it was sig'driving_value that used to fail silently in synthesis.
I don't use buffer ports now because variables can drive both ports and nodes in process scope.

-- Mike Treseler

Tue Dec 13, 2011 3:31 am   

On Dec 5, 8:29 am, Andy <jonesa...@comcast.net> wrote:

Driving value:
Ports of mode out have identical semantics to ports of mode buffer.

Jim

Thu Dec 15, 2011 4:11 pm   

On 12/05/11 09:44, Tricky wrote:

Other than on top-level, we use type BUFFER for all our block output ports. We've not had any trouble with that for over 14 years now.

Kind regards,

Pieter Hulshoff

Mon Jan 02, 2012 6:17 pm   

Tricky wrote:


The only reason people started using OUT in stead of BUFFER is because of
its name. I would say if the names were reversed, everybody still would
have used OUT with the bonus of not having to resort to ugly things a
internal signals to be able to read back the value of such a port, let
alone using INOUT for that reason.

In our company BUFFER has always been the standard for outputs. Never had
much trouble with that, except on top level, where foundries insisted on
OUT. But that was easy to fix.

Now with VHDL-2008, things have relaxed a bit more, so you can even mix
BUFFER and OUT.

--
Paul Uiterlinden
www.aimvalley.nl
e-mail addres: remove the not.