AR# 9296

12.1 Timing/Constraint - How do I perform skew checking with the BUFGMUX?

Description

My design has two clocks in the BUFGMUX, and has a period constraint on both. If one of the two clocks drives synchronous elements before the BUFGMUX, and other synchronous elements after the BUFGMUX, how do I perform skew checking between these two synchronous elements?

Solution

To perform skew checking for elements before and after the BUFGMUX, you can apply a FROM:TO constraint. If the elements before the BUFGMUX are grouped in TIMEGRP A, and the elements after are grouped in TIMEGRP B, the syntax is as follows:

TIMESPEC TS01 = FROM A TO B 12ns;

Another option is to have related PERIOD constraints for TIMEGRP A and TIMEGRP B. If these two PERIOD constraints are related to each other, then the clock skew will be analyzed correctly.

For more information, see (Xilinx Answer 7221).

AR# 9296
Date 12/15/2012
Status Active
Type General Article