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AR# 12702

4.1i Virtex-II PAR - DDR IOBs may be placed in an unroutable configuration.


Keywords: DDR, unrouted, unroutable, IOB

Urgency: Hot

General Description:
The 4.1i release contained a bug fix that introduced a new problem regarding DDR IOB placement. The change incorrectly causes a placement optimization algorithm to run that does not take into account the routing limitations of DDR IOBs due to shared clock routing resources.

NOTE: For more information on DDR IOB clock routing limitations, please see (Xilinx Answer 11747).


This problem is fixed in the latest 4.1i Service Pack, available at:
The first service pack containing the fix is 4.1i Service Pack 2.

Meanwhile, the problem can be avoided by locking all DDR IOBs and prohibiting any empty IOB sites that have shared DDR clock connectivity.
AR# 12702
日期 10/23/2008
状态 Archive
Type 综合文章