Placement constraint of SRL16

[surf99]

Hi,

Is there a way to constraint the placement of a SRL16 to a specific LUT location (F-LUT or G-LUT) within a slice?

I am using Spartan-3E.

Thanks a lot.

[bwade]

Yes, use the BEL constraint to do this. I think the possible values for S3e are F and G.

[surf99]

Thanks bwade.

I had tried that earlier but it seems the values "F" or "G" only applicable to LUT instances. I gave me error for SRL16 instantiation.

The error:

ERROR:Pack:313 - Unable to combine the following symbols into a single slice:
       Shift symbol "clbc0r0lutf00/SRLC16E" (Output Signal = clbc0r0lutf00_x)
   Function generator clbc0r0lutf00/SRLC16E has a site constraint other than
   "G".  These symbols are part of a collection of symbols which have
   restrictive placement or routing requirements.  The collection is:
       The RPM "hset"

-------------------------

If I don't constrain the placement, by default G-LUT will be used. But I would like to have control over where to use F-LUT and where for G-LUT.

Thanks.

[bwade]

My take on this error is not that Pack is rejecting the BEL constraint in general but that it thinks this specific constraint creates a conflict with your RPM some how. If it weren't trying to follow the BEL constraint there would be no error. What other constraints are involved besides RLOC constraints?

[bwade]

A collegue has reminded me of a hardware restriction where it is not possible to put an SRL in the F LUT unless the G LUT is also used for an SRL. If you are trying to constrain to the F LUT then that is probably why the error is occurring.