Report High Fanout Nets Options - 2023.2 English

Vivado Design Suite User Guide: Design Analysis and Closure Techniques (UG906)

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2023.2 English


In the Results Name field at the top of the Report High Fanout Nets dialog box, specify the name of the graphical window for the report.

Equivalent Tcl option:

 -name <windowName>


Minimum and maximum limits can be set to report only nets with the specified fanout.

Equivalent Tcl commands:

-fanout_greater_than 1 
-fanout_lesser_than 100000 


It is possible to limit the report based on objects. You can scope the report to specific hierarchical cells. When selected, all the sources are in the scoped cell. You can also report on clocks. By default, clocks are not reported but these can be specified in the report using a switch.

Equivalent Tcl commands:

-cells [get_cells <hierarchical cell>] 
-clocks [get_clocks <clock object>] 

Max Nets

By default, 10 nets are reported. It is possible to change this by specifying the -max_nets switch. The worst case slack on the net can also be added to the report.

Equivalent Tcl commands:

-max_nets <n> 

Load Distribution

Load types, clock regions, and SLRs can be added the report. If access to all is required, the command must be run multiple times.

Equivalent Tcl commands:



It is possible to show a histogram containing the fanout counts and the number of nets in a given bucket. This histogram can be used to determine if lower fanout nets represent a challenge if they are high in number. This table is only available in text mode. An example of the table is shown in the following figure.

Figure 1. Histogram Table

Equivalent Tcl command:

Note: Fanout is also shown in timing reports for each net and can be determined using the FLAT_PIN_COUNT property on nets.

To address high fanout issues, refer to this link and this link in UltraFast Design Methodology Guide for FPGAs and SoCs (UG949).