When closing timing on challenging designs, users might choose to run many
different place_design directives to select the best timing result. Auto directives use
machine learning to predict the best directives to run. Users can benefit by only
running these directives instead of the full sweep of directives listed in Available Directives.
Note: When
running with the Auto directives, the directive setup happens slightly later in the
flow than when the directive is directly specified which can result is slightly
different results.
Machine learning prediction of directives have a margin of error. As a
consequence, it is recommended to run 3 Auto_n directives and take
the best result. The directives predicted are equivalent to the ones mentioned in Available Directives, so there is no benefit in running auto directives in
addition to these. The directive selected by the tool is reported in the log file. An
example of the message is as
follows:
INFO: [Place 30-1947] Predicted directive using ML models is: EarlyBlockPlacementTo enable the feature, set the place_design -directive
<value> where value is:
- Auto_1
- High performing predicted directive
- Auto_2
- Second best predicted directive
- Auto_3
- Third best predicted directive