In Low Reuse mode, reuse is determined by the
<objects> -incremental <reference>.dcp switch. In this mode:
- The user can target cell types, hierarchical cells, clock regions and SLRs to be reused.
- The Target WNS is always 0.
- Incremental directives are ignored and the directives from the default place and route algorithms are used.
Low reuse mode is most effective on designs that are exhibiting challenges to the place and route in specific areas. Examples of use cases are:
- Reusing Block Memory or DSP placement from a good run can improve the total number of good runs at each place and route iteration.
- Reusing a particular level of hierarchy that closes timing intermittently.
You can determine if the tool is in low reuse mode by examining the log file after place_design has started for the following message:
INFO: [Place 46-42] Incremental Compile is being run in Low Reuse Mode.