AR# 32457

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

Description

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?

Solution

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 05/23/2014
Status Archive
Type General Article