Answers Database
PPR 5.2: What are the SaveSig (S), eXternal (X) netflags?
Record #284
Product Family: Software
Product Line: XACT FPGA
Product Part: ppr
Product Version: 5.0
Problem Title:
PPR 5.2: What are the SaveSig (S), eXternal (X) netflags?
Problem Description:
Solution 1:
All of the net-based constraints supported in pre-5.0 versions of PPR
are still supported in 5.0, 5.1, and 5.2. The Save (S) flag and the External (X) Flag are both suppo
rted through the XNF file, and should have the same effect as they had for designs processed with pr
ior versions.
The X attribute on a net tells PPR to ensure that the net is placed outside
of a CLB, rather than internal to a CLB. If using the Xchecker to debug
your design in circuit, using the X attribute makes it more likely for your
signal to be a probable point.
The S attribute on a net tells the XACT tools to save this signal. The
S attribute is useful if you want a net preserved in your placed and routed implementation. If you
are processing a design that is incomplete and you want to preserve the net and the associated logic
so that PPR can give you an
accurate estimate of the resource utilization, then use this attribute. Though you can also use th
e -savesig attribute with XNFPREP to more easily
accomplish this problem.
End of Record #284 - Last Modified: 11/15/96 18:56 |
