Re: EXTERNAL: Re: [vhdl-200x] Sizing of variables and signals from initial values

From: Jim Lewis <Jim@synthworks.com>
Date: Thu Apr 25 2013 - 09:51:10 PDT
Hi Andy,
> Adding additional operators is often clumsy, unnecessarily
 > adds bulk to the language, and needless implementation work
 > for the tool vendors.

Some have requested the ability to create a target sized result.
I would be concerned if this were to impact something other than
+ and -.  Going further for + and -, I would only want it to be
able to produce accumulate and lossless operations and not general
resizing.

In addition, how would it work for multiple operator expressions:
Y17 <= (A16 + B16) + (C16 + D16) ;


 > (e.g. "which addition operator do I use here?").
It would take some care with the operator symbols.
Taking a WAG at it, accumulate could be @+
and lossless could be #+.  Once established, I think
people know the difference between accumulation and
summing.


> After thinking about it last night, my new-for-vhdl-2008 trick for counters might be (to borrow a page from your paper):
>
> Variable count : ufixed(3 downto 0);
>
> Variable overflow : ufixed(0 downto 0);
>
> (overflow, count) := count + 1;
>
> (overflow, count) := count - 1; -- using fixed_wrap

I like this.  I will add it to the slides David and I did.
Fixed_saturate is on the package instance of fixed_pkg.
Do you use your own instance instead?


Jim
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Received on Thu Apr 25 09:52:18 2013

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