Answers Database

EDIF2XNF 5.x: S Netflag does not save unconnected nets and symbols


Record #397

Product Family:  Software

Product Line:  Mentor

Problem Title:
EDIF2XNF 5.x: S Netflag does not save unconnected nets and symbols


Problem Description:
The S property can be appended to nets as a NETFLAG property, so that the
net can be left sourceless or loadless without the associated logic being
deleted from the netlist by XNFPrep.  This is useful for making preliminary
evaluations of a design that is not complete. Unfortunately, the S property
is seemingly ignored by XNFPrep when it is added to a Mentor design.

The cause of this problem is that EDIF2XNF 5.x does not write the dangling
net itself into the XNF netlist, although it does write the record
indicating the presence of the S flag. For example, in a normal XNF file, a
fully-attached IBUF record might look like this:

   SYM, BUFME, IBUF, SCHNM=IBUF, LIBVER=2.0.0
   PIN, O, O, OUT
   PIN, I, I, IN
   END

The I pin and O pin are both represented. If the O pin were dangling, you
would still expect it to be instantiated in the XNF as shown above. If the
net had an S flag on it, you would also expect to see the following line:

   SIG, OUT, S

EDIF2XNF writes the SIG line correctly, but leaves off the corresponding
PIN record for the attached symbol. Following our above example, if the net
OUT were loadless, EDIF2XNF would write out:

   SYM, BUFME, IBUF, SCHNM=IBUF, LIBVER=2.0.0
   PIN, I, I, IN
   END

XNFPrep now loses the connection between the SIG line and the IBUF record.


Solution 1:

Attach a "dummy" buffer to the dangling end of the net. This will cause the
PIN records for the net to be written correctly in the XNF. The buffer
itself will be deleted automatically from the netlist.



End of Record #397