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3.1i Virtex MAP - Some eligible registers are not being packed into IOBs.
Keywords: registers, flops, FFs, -pr ,IOB=TRUE, IOB
A case has been seen where 3.1i MAP, when run with the switch "-pr b,"
did not pack as many registers into IOBs as it was able to in 2.1i.
1 This problem is fixed in the latest 3.1i Service Pack available at:
http://support.xilinx.com/support/techsup/sw_updates/. The first
service pack containing the fix was Service Pack 1.
2 This problem can be worked around by assigning the same
BLKNM attribute to all comps that belong in the same IOB.
The following is an example of UCF syntax:
INST "pad_name" BLKNM = "IOB1" ;
INST "ibuf_name" BLKNM = "IOB1" ;
INST "inreg_name" BLKNM = "IOB1" ;