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AR# 20532

EDK 6.3 - OPB_EMC 1.10.b input/output/3-state registers cannot be packed into IOBs


General Description: 

The registers in the OPB_EMC and the PLB_EMC, pushed outside of the IOBs, which causes reasonable offset-out-after constraints to fail.  


The input register resets are qualified in "emc.vhd" by input_datareg_rst. Because this signal is not the same as the 3-state and output register reset signals (Bus2IP_Rst), these registers cannot share the IOB so one of the two is left outside and that makes it fail timing. 


The reason that the 3-state registers cannot be pushed into the IOB is because the registers are optimized down to one register and all of the 3-state lines are driven from the one slice register. A save attribute will probably keep XST from doing this optimization.  


This has been fixed in emc_common_v2_00_a, which is included in OPB_EMC_V2_00_A.


This problem is fixed in the latest 6.3 EDK Service Pack, available at: 

The first service pack containing the fix is EDK 6.3 Service Pack 2.

AR# 20532
Date Created 09/03/2007
Last Updated 05/16/2014
Status Archive
Type General Article