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C5505 computating Large FFTs does only work partially

Hi there,

I try to implement a 8192 Bit FFT on the C5505 using the HWAFFT.

First I use the HWA Bitreverse and split the data in 8.
HWAFFT each part and at the end use a 3 stage FFT routine on the main processor to combine the data.

To gain speed while just testing I used 128 and 256 bit FFT and it works like a Charm.

But when using 512 or 1024 I get wrong results. The peaks have the wrong distance to each other and are repeated multiple times.
The data is already faulty after the HWAFFT 

Without splitting the 1024 FFT does work properly.

Correct result (8x256)

Wrong result (8x 512)

The second graph is actually double the size but just mirrored.

From one to another I just replaced every 256 with 512 in my code