Conditional compiling, exists ?

Tue Jan 19, 2010 3:03 pm   

Hi.

Sorry for the naive question.

Is there a way to implement conditional compiling
in VHDL (as in C for example, #ifdef... #endif).

I would like to have a source with two variants
that I may decide to compile one way or another
but there are several small differences spread
across the code so...

(two separate files is difficult to maintain in sync
while design progresses)
(commenting and uncommenting parts is prone to mistakes
and messy)

Is there any hope to make my life easier ?


Luis. C.

Tue Jan 19, 2010 4:35 pm   

On Tue, 19 Jan 2010 14:03:57 +0000, LC <cupidoREMOVE_at_mail.ua.pt> wrote:


You might want to look at "m4" which is a macro preprocessor intended as
a front end to the "normal" compilation process. It's a pretty standard
Unix utility (or did it pre-date Unix?) that's now on most (all?) *ix
distributions. There are binary versions for Windows (Cygwin and native
code) and Mac.

For more info, hop over to the Wikipedia entry and go from there.

--
Rich Webb Norfolk, VA

Tue Jan 19, 2010 4:57 pm   

LC <cupidoREMOVE_at_mail.ua.pt> writes:


See generate.

Petter
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Tue Jan 19, 2010 5:05 pm   

On 19 Jan, 14:03, LC <cupidoREM...@mail.ua.pt> wrote:

I think there may be a couple of options:

1. Have 2 different architectures for the same entity and use
configurations to change which one to compile
2. Use generics to control what gets compiled based on the values:

for example:

reg_gen : if add_register generate

process(clk)
begin
if rising_edge(clk) then
out <= in;
end if;
end process;
end reg_gen

no_reg_gen : if not add_register generate

out <= in;
end no_reg_gen;


Given what you already said (2 variants on the same thing) you
probably want configurations (someone else will have to explain this
mystical VHDL concept).

Tue Jan 19, 2010 5:13 pm   

LC wrote:


There is no preprocessor.
I use packaged constants with regular
vhdl conditional statements or generics.

-- Mike Treseler

Wed Jan 20, 2010 2:24 pm   

Many thanks for the tips.

LC.

Wed Jan 20, 2010 5:04 pm   

LC wrote:

Hi LC,
we also have a little technote about this very issue:

http://www.doulos.com/knowhow/fpga/technotes/index.php#Technote2

regards
Alan

P.S. We ask you to register for it - but as I remember there's a tickbox
somewhere for you to opt out of being contacted again if you don't want
to be, Alan


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Thu Jan 21, 2010 12:59 am   

Alan Fitch wrote:

Hi Alan,

I could not imagine a better technote on the subject
You guys rock !

Many Thanks.

Luis C.