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AR# 39988

Virtex-4 - I get a DCM feedback warning starting with: PhysDesignRules:1236. Can it be ignored?


When implementing a design I get the following warning. Is it valid?

WARNING:PhysDesignRules:1236 - Unknown DCM_ADV feedback loop. The signal
dcm1_u/CLKFB_IBUFG on the CLKFB pin of DCM_ADV comp dcm1_u/DCM_ADV_INST was
driven by an IOB site but the signal loop could not be traced back to the
CLK0 pin of comp dcm1_u/DCM_ADV_INST. The signal out the CLK0 pin must drive
an IOB input pin with programming out to the PAD.


You need to ensure that the feedback path of the DCM is correct. The FEEDBACK must originate from the same DCM it is being fed back to; it cannot be sourced from another CLK or DCM.
AR# 39988
Date Created 01/25/2011
Last Updated 12/15/2012
Status Active
Type General Article
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