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

AR#	32457	Search For Another Answer
Topic	SW-Timing Analyzer/TRCE
Last Updated	04/20/2009
Status	Active

Description

Keywords: arrival time

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.