Subject: Re: [vhdl-200x] Minutes for VHDL-200X-FT meeting, San Jose Dec 4, 2003
From: Munden Rick (Rick.Munden@Siemens.com)
Date: Wed Dec 10 2003 - 19:43:42 PST
Jim,
See embedded comments.
Rick
Jim Lewis wrote:
> "if" for conditional signal assignment is ment as a trial
> balloon.
>
> We do need to remain backwards compatible, so when
> I said deprecate, I was only thinking of discouraging
> future usage of when and not eventual removal. So
> strike the word deprecate as I did not mean removal.
>
> I would be against having different syntax in concurrent
> and sequential assignment. We need consistency in
> the different contexts. I would prefer to support
> either both in both contextes or stick with "when".
>
> As Andy pointed out, this would be yet another way to
> do the same thing, but I don't always think this is bad.
> As a whole, I think we should be gravitating toward ways
> that are more concise and more readable.
>
> With respect to synthesis register coding styles,
> we have made the following progression of yet another
> way of doing things:
>
> past: wait until Clk = '1' and Clk'event ;
> current1: wait until Clk = '1' ;
> current2: wait until rising_edge(Clk) ;
> future: wait until rising_edge(Clk) and load_enable = '1' ;
>
> I like readability that everyone intuitively understands,
> so I prefer current2: "wait until rising_edge(Clk) ;".
> (However, I do have some concerns about current2 simulating
> slower than current1).
Current1 and current2 have different meanings. If current1 is what you
mean, you should use it and take the faster simulation times.
I don't see anything about this in the minutes.
>
> With "when" many confuse the statement with selected
> signal assignment and overlook prioirity select logic.
> This includes experienced users reviewing code.
> With "if" this would be harder to miss:
>
> Y <= A if SelA = '1' else
> B if SelB = '1' else
> C ;
>
> If you disagree with me, please let me know and I
> will make sure that this is modeling and productivity
> issue rather than a fast-track issue.
To me it is the "else" that signals priority encoding. So I guess I
disagree.
>
> Cheers,
> Jim
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