Digital Signal Processing - IP and Algorithms

[lrsmith]

Is the FFT Core (7.1) capable of accepting bit-reversed inputs and outputing the data in natural order?  Specifically, I have a signal that I want to process using a forward FFT core configured to output the result in bit-reversed order.  I then want to take the resulting data into an inverse FFT core, also configured to output the data in bit-reversed order, resulting in its output data being in natural order.  I am able to successfully simulate with both cores configured for natural order inputs/outputs, but to save on resoursces/latency, I would like to configure the forward and inverse FFT cores to use bit-reversed outputs.

[lrsmith]

Any insight on this question would be much appreciated, even if the answer is no.  I'm led to believe the FFT core is not compatible with bit-reversed inputs, but would like confirmation from those more experienced in the matter since I am relatively new to using this core.

[bpelger]

Actually I'm interested in this topic too.

An option for bit-reversed inputs would be especially useful for doing fast convolution using overlap-discard and overlap-add methods. Since this is basically a FFT followed by an IFFT, it would be very resource efficient if both cores could work with bit-reversed outputs and inputs respectively.

Unfortunately this is not possible since the FFT/IFFT cores support  only bit reversed outputs, and I don't see an easy way of getting a bit-reversed input IFFT from a bit-reversed output IFFT. 

I wonder how am I supposed to implement fast convolution using coregen-FFTs. The only options I can think of is using the BRAM-expensive natural order FFT and IFFT.

[bwiec]

bpelger is correct, Bit reverse input is not supported at this time.

Natural order FFT/IFFT will allow implementation of fast convolution algorithms.

[bpelger]

I just had the impression that fast convolution is such a standard task, that I must be missing an option or something else in coregen. Thanks for the clarification. 

[ywu]

Could you please open a webcase requesting FFT core supporting inputs in bit-reversed order? If yes, please send me the webcase number via PM.

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bpelger wrote:

I just had the impression that fast convolution is such a standard task, that I must be missing an option or something else in coregen. Thanks for the clarification. 

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[tomnguyen_2]

Did anyone open up a ticket for this as mentioned in the last response by Jimwu?
I am very interested in FFT core with bit reversal output and input back into IFFT (with the same bit reversal order) and get natural order out.

Thanks

[bwiec]

Yes, a case was opened for this. The possibility for bit reversed input is being investigated. No firm plans at this point, though.

I recommend you contact your FAE and provide feedback to them so they can communicate with marketing.