The Report CDC (report_cdc) command performs a
structural analysis of the clock domain crossings in your design. You can use this
information to identify potentially unsafe CDCs that might cause metastability or data
coherency issues. Report CDC is similar to the Clock Interaction report, but Report CDC
focuses on structures and related timing constraints. Report CDC does not provide timing
information because timing slack does not make sense on paths that cross asynchronous
clock domains.
Report CDC identifies the most common CDC topologies as follows:
- Single bit synchronizers
- Multi-bit synchronizers for buses
- Asynchronous reset synchronizers
- MUX and CE controlled circuitry
- Combinatorial logic before synchronizer
- Multi-clock fanin to synchronizer
- Fanout to destination clock domain
For more information on the report_cdc
command, see this link in the
Vivado
Design Suite User Guide: Design Analysis and Closure
Techniques (UG906). Also, see report_cdc in the
Vivado
Design Suite Tcl Command Reference Guide (UG835).
Specific constraints should be applied to prevent default timing analysis on asynchronous clock domain crossings.