10-09-2011 07:08 PM
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.
10-09-2011 10:47 PM
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.
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.
10-10-2011 07:09 AM
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?
10-10-2011 11:02 AM
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.