Hi,

In most of the cases, the core takes fewer cycles than the FFT accelerator. However, the difference in number of cycles is comparatively less for small FFT and becomes much more significant for large FFTs.

For more information kindly refer to the FFT Accelerator (FFTA) chapter on ADSP-2158x Hardware Reference Manual. The link for the manual is given below:
www.analog.com/.../SC58x-2158x-hrm.pdf

If you are looking for a way to compare the performance of the FFT accelerator vs the performance of the core, the comparison data is already available, we would request you to kindly refer to the ADSP-214xx Hardware Reference Manual on page 444/1304 (Pg.No 7-80)which does the throughput comparison of the Hardware Accelerator w.r.t Core for FIR/IIR and FFT, which might be helpful to you.

The link for the manual is given below:
www.analog.com/.../ADSP-214xx_hwr_rev1.1.pdf

As you can see, as the window size increases, initially the accelerator consumes more cycles than the core. However, after a threshold, the accelerator performs better than the core.

Regards,
Santhakumari.K

Hi,
Thanks.  Does the graph in the ADSP-214xx hardware reference really apply to the ADSP-2158x?  In the document here: 

https://ez.analog.com/dsp/sharc-processors/adsp-sc5xxadsp-215xx/w/documents/5133/how-fft-accelerator-ffta-on-adsp-sc58x-adsp-2158x-is-different-as-compared-to-adsp-214xx-processors-what-are-the-major-features-of-ffta-on-adsp-sc58x-adsp-2158x 

It states that "FFT Accelerator on ADSP-SC58x/ADSP-2158x is a completely new design as compared to the FFT accelerator on ADSP-214xx processors."

Is there a similar graph available for the ADSP-2158x?

If they perform the same, then the FFT accelerator performance is never as fast as the core.(ADSP-214xx hardware reference fig. 7-15)  In what way then can the FFT accelerator be used to any benefit?

The point about the increased window size applies to the FIR throughput graphs of increasing 'N' value, not the FFT.

Thanks,
Matt

Hi,
Thanks.  Does the graph in the ADSP-214xx hardware reference really apply to the ADSP-2158x?  In the document here: 

https://ez.analog.com/dsp/sharc-processors/adsp-sc5xxadsp-215xx/w/documents/5133/how-fft-accelerator-ffta-on-adsp-sc58x-adsp-2158x-is-different-as-compared-to-adsp-214xx-processors-what-are-the-major-features-of-ffta-on-adsp-sc58x-adsp-2158x 

It states that "FFT Accelerator on ADSP-SC58x/ADSP-2158x is a completely new design as compared to the FFT accelerator on ADSP-214xx processors."

Is there a similar graph available for the ADSP-2158x?

If they perform the same, then the FFT accelerator performance is never as fast as the core.(ADSP-214xx hardware reference fig. 7-15)  In what way then can the FFT accelerator be used to any benefit?

The point about the increased window size applies to the FIR throughput graphs of increasing 'N' value, not the FFT.

Thanks,
Matt

Hello Matt,

Unfortunately we don't have similar kind of comparison data available for ADSP-215xx processor.

However, please refer the attached image "FFTA.PNG" that show more details on FFT performance benchmark (both core and accelerator)for ADSP-SC58x which might be helpful to you.

Also note that, The FFT accelerator units are capable of performing the filters and FFT without core intervention.

There is also a good discussion related to the FFT accelerator APIs available at the discussion below.

ADSP-SC58x/2158x FFT Accelerator: Example code
ez.analog.com/.../adsp-sc58x-2158x-fft-accelerator-example-code

Regards,
Santhakumari.K