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AR# 8252

LogiCORE FFT - Which FFT cores are supported by Spartan-II/E architecture?


In the CORE Generator GUI, the supported families for the 16-point, 64-point, 256-point, and 1024-point Xilinx FFT cores are: Virtex, Virtex-E, Virtex-II, and Virtex-II Pro.

As they have similar architectures, are the Spartan-II and Spartan-IIE families supported as well?


The Spartan-II family of FPGAs is not supported by these FFTs, as none of the parts in this family are large enough to work with these FFT cores.

The only FFT core available for the Spartan-II device is the parameterizable 32-point FFT. However, not all the parameters create a core that will fit in the largest Spartan-II, due to the RLOCs on the core. Enough slices exist in the device, but the shape of the core (as defined by the RLOCs) may be larger in height or width than the largest Spartan-II device. Smaller values of data input-width and twiddle factor-width create usable cores in Spartan-II.

The same is true for Spartan-IIE devices, although larger values can be supported for the core's parameters as the family has a larger device.

If the selected parameters create a core that is too large, PAR will fail and report messages similar to the following:

"WARNING:Place:78 - The SLICE component "uut_fft/N169" could not be placed.

SLICE "uut_fft/N169"."
AR# 8252
Date 07/28/2010
Status Archive
Type General Article