Description

I am using a DCM with external feedback. The output feedback clock is generated with the ODDR clock forwarding scheme. I have included the appropriate FEEDBACK constraint on the forwarded clock on the DCM and I still get the following warning during MAP:

"WARNING:PhysDesignRules:1236 - Unknown DCM_ADV feedback loop"

What does the warning mean?

解决方案

This warning can be safely ignored and timing will be analyzed properly. A CR has been filed to investigate this issue and correct the message.