Why are the results of my interpolating half-band filter incorrect when I use the optimize for speed option?
This issue is resolved in the FIR Compiler v.3.1.
This issue is due to a bug in the way the center tap is created for interpolating half-band filters when the optimize for speed option is used. You can work around this issue by not using the optimize for speed option.
See (Xilinx Answer 29138) for a detailed list of LogiCORE FIR Compiler Release Notes and Known Issues.