Report Asynchronous CDC Command

The Timing Analyzer’s Reports > Clock Domain Crossings > Report Asynchronous CDC... command allows you to classify and report all asynchronous clock-domain-crossing (CDC) transfers in your design.

Asynchronous CDCs include single-bit transfers, multibit transfers, and asynchronous reset CDCs. Designs often contain unintended CDCs or transfers. Use this report to ensure that the Timing Analyzer correctly detects all CDCs.

Table 1. Report Asynchronous CDC Information Settings
Option Available Settings
Clocks Filters the report to only show CDCs that originate from From clock and terminate at To clock.
Targets Filters the report to only show CDCs that originate from From register and terminate at To register. Both the From and To must be registers. This option is optional with the Clocks option.
Entries Limits the number of entries that are reported per CDC category
Detail Chooses whether to show a summary of all CDC’s or give detail on each individual CDC
CDC Categories Specifies the CDC categories to be reported.
Report panel name

Specifies the name of the report panel. You can optionally enable File name to write the information to a file. If you append .htm or .html as a suffix, the Timing Analyzer produces the report as HTML. If you enable File name, you can overwrite or append the file with latest data.

Tcl command

Displays the Tcl syntax that corresponds with the GUI options you select. You can copy the command from the Console into a Tcl file.

The summary view of the Asynchronous CDC Report provides an overview of the number of CDC’s that fall into each category in your design. CDC Count gives the number of topologies detected for a category. Total Transfer Width shows the total number of CDC crossings for a category. This value is different than CDC Count for multibit CDC’s because each topology consists of multiple crossings.

The full view of the Asynchronous CDC report shows the source and destination registers and clocks for each detected CDC topology in your design. You may click on any row of this report. Clicking on a row that contains the name of a CDC category brings up the description for that category and associated Design Assistant rules that check for such topologies. Clicking on a row that contains a CDC brings up detailed information on that CDC in the CDC Statistics table. The information available varies depending on the topology of the CDC.