Using Synplify, how do I synthesize the OE FF in the SpartanXL, XC4000XLA/XV, and Virtex IOB?
For Spartan-XL and XC4000XLA/XV devices, the methodology was introduced in M1.5i as a hard macro within Epic. Please see (Xilinx Answer 5140) for details.
For Virtex, the fact that the FF is generic ("anonymous" ), should not be an issue if MAP knows how to pull the FF into an IOB location. The current Virtex mapper knows how to do this if the FF has the "IOB=TRUE" attribute. Please see (Xilinx Answer 5675) for details on IOB flip-flops within Virtex.
Synplify does provide a mechanism for passing attributes through the HDL. Please see (Xilinx Answer 2867) for details on merging flip-flops to the XC4000XLA/XV and Spartan-XL families.
Please see (Xilinx Answer 9178) for details on merging flip-flops to the Virtex/Virtex-E and Spartan-II families.