Re: Xilinx Synthesis Warning

Hello,

Xilinx is giving me the following warning during synthesis:

================================================== =======================
* Low Level
Synthesis *
================================================== =======================
WARNING:Xst:1988 - Unit <control>: instances <Mcompar__cmp_lt0001>,
<Mcompar__cmp_ge0001> of unit <LPM_COMPARE_1> and unit <LPM_COMPARE_4>
are dual, second instance is removed
WARNING:Xst:1988 - Unit <control>: instances <Mcompar__cmp_lt0000>,
<Mcompar__cmp_ge0000> of unit <LPM_COMPARE_1> and unit <LPM_COMPARE_4>
are dual, second instance is removed

Could someone please explain to me what this warning means? Can I
safely ignore it? I have followed the link for the warning code to the
Xilinx page, but it returns "page not found".

Thanks,

Mike

Moikel

On Mar 11, 8:01 pm, Moikel <obviouslyadu...@gmail.com> wrote:
> Hello,
>
> Xilinx is giving me the following warning during synthesis:
>
> ================================================== =======================
> * Low Level
> Synthesis *
> ================================================== =======================
> WARNING:Xst:1988 - Unit <control>: instances <Mcompar__cmp_lt0001>,
> <Mcompar__cmp_ge0001> of unit <LPM_COMPARE_1> and unit <LPM_COMPARE_4>
> are dual, second instance is removed
> WARNING:Xst:1988 - Unit <control>: instances <Mcompar__cmp_lt0000>,
> <Mcompar__cmp_ge0000> of unit <LPM_COMPARE_1> and unit <LPM_COMPARE_4>
> are dual, second instance is removed
>
> Could someone please explain to me what this warning means? Can I
> safely ignore it? I have followed the link for the warning code to the
> Xilinx page, but it returns "page not found".
>
> Thanks,
>
> Mike

Can't say for sure, but it looks like some intermediate stage in the
synthesizer decided to build a "less than" unit as well as a "greater
than or equal" unit, and the warning reflects its realization that, in
hardware, the two will always produce the opposite (i.e. dual) output,
hence it is replacing one of them with an inverter. My guess: this is
probably OK to ignore.

- Kenn

kennheinrich@sympatico.ca

On Mar 11, 5:01 pm, Moikel <obviouslyadu...@gmail.com> wrote:
> Hello,
>
> Xilinx is giving me the following warning during synthesis:
>
> ================================================== =======================
> * Low Level
> Synthesis *
> ================================================== =======================
> WARNING:Xst:1988 - Unit <control>: instances <Mcompar__cmp_lt0001>,
> <Mcompar__cmp_ge0001> of unit <LPM_COMPARE_1> and unit <LPM_COMPARE_4>
> are dual, second instance is removed
> WARNING:Xst:1988 - Unit <control>: instances <Mcompar__cmp_lt0000>,
> <Mcompar__cmp_ge0000> of unit <LPM_COMPARE_1> and unit <LPM_COMPARE_4>
> are dual, second instance is removed
>
> Could someone please explain to me what this warning means? Can I
> safely ignore it? I have followed the link for the warning code to the
> Xilinx page, but it returns "page not found".
>
> Thanks,
>
> Mike

To expand on what Kenn said:

XST has found something like this:

A = '1' when (B > C) else '0';
D = '0' when (C >= B) else '1';

Well, it turns out that 'A' and 'D' are the same, so it throws the 2nd
equation away (2nd instance is removed), and substitutes 'A' for every
'D'.

You can ignore these warnings. Unless you're expecting the two
signals to be different.

G.

ghelbig@lycos.com