Retrofitting phys_opt_design Netlist Changes - 2022.1 English

Vivado Design Suite User Guide: Implementation (UG904)

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2022.1 English

The design flow involving retrofit is described in the following figure.

Figure 1. Design Flow Involving Retrofit

Two runs are involved, which are the “original run,” where phys_opt_design is run after place_design and the “replay run,” where phys_opt_design netlist changes are performed before placement.

After the original run, the phys_opt_design optimizations are saved to a Tcl script file using the Tcl command write_iphys_opt_tcl. The script contains a series of iphys_opt_design Tcl commands to recreate exactly the design changes performed by phys_opt_design in the original run. You can save the optimizations from the current design in memory or after opening an implemented design or checkpoint where phys_opt_design has performed optimization.

The same design and constraints are used for the replay run. Before place_design runs, the read_iphys_opt_tcl command processes the iphys_opt_design command script and applies the netlist changes from the original run. As a result of the netlist changes, the design in the replay run might be more suitable for placement than the original run. The design now incorporates the benefits of the phys_opt_design optimizations before placement, such as fewer high-fanout nets after replication and fewer long distance paths from block RAM outputs.

Similar to the phys_opt_design command, the read_iphys_opt_tcl command has options to limit the replayed design steps to certain types, such as fanout optimization, block RAM register optimization, and rewiring.