Why does my Virtex-5 multiplier that is not fully pipelined give incorrect output results in post-MAP simulation, post-PAR simulation, and hardware?
This is a known issue that causes the MAP to incorrectly use the MREG.
You can work around the issue by setting the following environment variable:
XIL_MAP_NO_DSP48E_AUTOREG = 1
For information on setting environment variables, see (Xilinx Answer 11630).
This problem has been fixed in the latest 8.2i Service Pack available at:
The first service pack containing the fix is 8.2i Service Pack 2.