Re: pragmas

Alain RAYNAUD (alain_raynaud@mentorg.com)
Mon, 6 Jul 1998 10:01:37 +0200

On Jul 3, 2:10pm, Smith, Douglas J wrote:
>
> At the recent face-to-face meeting we discussed pragmas. One of
> the issues was a means of communicating to a synthesis tool that
> it should map directly to a multiplexer. As such I have am proposing
>
> // rtl_map_to_mux
>
> which can be associated with a case or if statement.

Sorry I missed the face-to-face meeting, so maybe this has been discussed
already.

However, I fail to understand the point of providing such a pragma. What does
it do?

As a tool writer, what should I do with it? Why not trust the optimizing engine
to generate whatever logic is best for the target architecture? What if the
same source code (with the pragma) is used to target completely different
architecture?

I don't really believe in the source code instructing the synthesizer of which
algorithm is best. Source code is known so stay around much longer than what
the original developer thought, and I'm afraid many pragmas would become
irrelevant in the process.

Basically, such pragmas tend to pollute the code with additional information
that may or may not be used. And, as you pointed out, one could make up
hundreds more of these for all kinds of cases. Until a new mapping algorithm
makes them all obsolete.

Alain.

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 Alain RAYNAUD                                            META SYSTEMS 
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