Answers Database

PPR: Guidelines for using manually edited LCAs as PPR guide files


Record #952

Product Family:  Software

Product Line:  FPGA Core

Problem Title:
PPR:  Guidelines for using manually edited LCAs as PPR guide files


Problem Description:
Guidelines and restrictions when using manually edited LCA files as guide files.


Solution 1:

An LCA file created by PPR may be manipulated in XDE and still be
used as a guide, *IF* only the XDE "SAFE mode" commands are used:
this includes operations like SwapBlk and SwapSig.  You should be
able to go into XDE, modify the placement and/or routing (including
unrouting some nets, and/or pre-routing critical ones).

Other, non-safe operations:

Among non-safe mode operations, the DeleteBlk command
can also safely be used to delete logic in an LCA that will be used as a
guide file.  Deleting blocks is *usually* safe (although DeleteBlk
is not available in XDE's safe mode, so the rule breaks down a bit).

DeleteNet:  There are some problems with using this operation when
modifying a guide file as you may end up with missing-but-used nets.
Since DeleteBlk will delete the appropriate pins (and nets, if the
last pin is deleted), it is recommended that any deletions be done
via the DeleteBlk command.

Other restrictions:

The original design needs to be generated by PPR, and it must
be PPR 5.0.0 or later.

Adding logic manually is not allowed if you plan to use the
resulting LCA as a guide (this is a non-SAFE mode operation).
The problem with adding logic with EditlLCA (XDE) is that EditLCA
will not write INTNET records for the nets that are internal to a CLB.
The INTNET records are required by PPR when uses an LCA file as
a guide.

Additionally, note that you must be very careful about any constraints
(in the netlist or in a CST file). In general, PPR processes constraints
first (before it does guide), and this can cause some problems.




End of Record #952