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AR# 32457

11.1 Timing Known Issue - OFFSET IN with FALLING keyword appears to be off by a whole clock cycle


When I review my OFFSET IN with FALLING keyword, I notice the clock arrival time was a whole clock cycle off when compared with the OFFSET IN with RISING keyword. 


In the timing report: 

Rising Edge Clock Arrival: -2.051 ns (both setup and hold) 

Falling Edge Clock Arrival: 12.949 ns (both setup and hold) 


I thought the clock arrival times are supposed to be the same; when is this going to be fixed?


The clock arrival times should be the same. This issue is caused by the negative phase-shifting performed in the DCM/PLL/MMCM components.  


To work around this problem, perform positive-phaseshifting; the clock arrival times will then be the same. 


This issue is scheduled to be fixed in the next major release of the software.

AR# 32457
Date Created 04/10/2009
Last Updated 05/23/2014
Status Archive
Type General Article