Why isn't symmetry exploited for the Multiply Accumulate Filter Architecture with Symmetric Coefficient Structure for an Interpolating filter and targeting a Virtex, Virtex-E, Virtex-II, Virtex-II Pro, Spartan-II, Spartan-IIE, Spartan-3, Spartan-3E, or Spartan-3A device?
When specified to use the MAC FIR structure for these devices, the MAC FIR v5.1 Core is used and, as is stated in the data sheet for the MAC FIR v5.1 Core, it does not utilize symmetry.
This problem does not affect Virtex-4, Virtex-5, or Spartan-3A DSP, in all versions of the FIR Compiler.
The limitation has been removed from the FIR Compiler v3.2 and utilization of symmetry will be supported for all families.
Please see (Xilinx Answer 29138) for a detailed list of LogiCORE FIR Compiler Release Notes and Known Issues.