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AR# 4778

A1.5/F1.5 PAR - PAR ignores constraint in pcf file for IOB placement

Description

Keywords: M1.5, par, pcf, bufg

Urgency: Standard

General Description : Some pin locking constraints entered directly into the physical constraints file (.pcf file) are ignored by par. The resulting placement has a constrained component placed in a different IOB than the one indicated in the .pcf file.

Solution

Detailed Description :
If the design contains an off-chip signal which is being routed to a global clock, and the user manually inputs the pin locking constraint into the .pcf file, par will ignore it if the IPAD is directly connected to a BUFG and the desired IOB is not a dedicated global clock pad.

Under the above circumstances, par will not generate any warnings or errors about the invalid constraint in the .pcf file and will place the IOB wherever there is a free global clock IOB.


Work-around:
There are two work-arounds.

First, the constraint can be entered into the .ucf file instead of the .pcf file. This results only in an error message being issued about the invalid constraint.

Second, an IBUF can be inserted between the IPAD and BUFG. This allows the designer to use the same .pcf file and results in correct placement of the constrained component.
AR# 4778
Date Created 08/31/2007
Last Updated 10/21/2008
Status Archive
Type General Article