In either standard or timing-driven mode, use incremental placement to preserve the timing of a design after a successful place-and-route, even if you change part of the netlist. Incremental placement has no effect the first time you run layout. During design iteration, incremental placement attempts to preserve the placement information for any unchanged macros in a modified netlist.
As a result, the timing relationships for unchanged macros approximate their initial values, decreasing the execution time to perform Layout. By forcing Designer to retain the placement information for a portion of the design, some flexibility for optimal design layout may be lost. Therefore, do not use incremental placement to place your design in pieces. You should only use it if you have successfully run Layout and you have minor changes to your design.
Incremental placement requires prior completion of place. Do not use incremental placement if the previous Layout failed to meet performance goals.
When the Lock Existing Placement option is selected in the Layout dialog box, all unchanged macros are treated as locked (fixed) placements during an incremental placement. This is the strongest level of control, but it may be too restrictive for the new placement to successfully complete. The default ON setting treats unchanged macro locations as placement hints, but alters their locations as needed to successfully complete placement. Refer to ChipEditor for details on locking macros.
For ProASIC and ProASICPLUS designs, you can export a GCF constraint file to get all of the constraint information. From the File menu, choose Export > Constraint Files, type a file name and click Save, and then select All GCF constraints in the Export GCF File dialog box. Blocks with locked placement constraints generate locked placement constraints, while the others generate initial placement constraints. You can edit a GCF file to remove existing constraints or add new constraints. You must then import the modified GCF file as well as the netlist back into Designer. See Importing Source Files for more information about importing files.