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AR# 12704

4.1i Virtex-II MAP - The mapper is rejecting a valid Virtex-II clock-forwarding scheme


General Description:

MAP is not recognizing the clock-forwarding structure of an output DDR flop, with one input tied high and the other tied low, as a forwarded clock. Therefore, when I use this configuration for external feedback, MAP fails with the following error:

ERROR:MapLib:289 - DCM symbol "DCM_A" (output signal=dcm_locked_out_c) CLKFB is driven by an input buffer, but neither CLK0, CLK2X or CLKFX of the DCM is driving loads off-chip.

However, this is a valid configuration for the DCM.


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.
AR# 12704
Date Created 08/29/2007
Last Updated 07/08/2010
Status Archive
Type General Article