AR# 2913

6.3i CPLD, CPLDFit - "WARNING: CPLD:819 or CPLD:823 - Clock CLK appearing in an OFFSET timespec currently must be explicitly declared as a global clock..."

Description

General Description:

When I place an OFFSET constraint on my design, the following message appears during implementation:

"WARNING: Cpld:819 - Clock CLK appearing in an OFFSET timespec currently must be explicitly declared as a global clock input (BUFG) in your design. The OFFSET constraint referring to this clock will be ignored."

Solution

The OFFSET constraint applies only to CPLDs when the clock is on a global clock net. This can be achieved by performing one of the following:

1. Placing the following constraint on the clock net

NET myclock BUFG=CLK;

(replace myclock with the name of the clock signal).

2. Inserting a BUFG component in the clock path immediately after the input pin.

Either of the above will force the CPLD Implementation tools to use a global clock pin of the CPLD for this input. You might also pin assign to a specific global clock pin if desired.

Currently OFFSET constraints may not be applied to clocks on non-global clock nets. To work around this issue, apply From:To constraints for the clock path and the data paths individually.

AR# 2913
Date 05/07/2014
Status Archive
Type General Article