FFT on nRF9160

[flau]

Hi Everyone,

I am wondering if anyone have done FFT with a nRF9160.  I found discussion about FFT on nRF52, but nothing on nRF9160.  Can it be done?  An example would be nice.  Thank you in advance.

Cheers,

Floyd

[Raoul]

Hi Floyd,

I haven't seen it done so far, but it's certainly possible!

Among the nRF52-related discussion you found, you might have seen references to the CMSIS-DSP Library, which supports performing FFTs. The CMSIS libraries are available for many Cortex-M devices, including the Cortex-M33 in the nRF9160.

The CMSIS-DSP library had to be added manually before, but is now distributed with Zephyr.

First off, add the following to your prj.conf (taken from this case):

CONFIG_CMSIS_DSP=y
CONFIG_NEWLIB_LIBC=y
CONFIG_FPU=y

#if  printf should be able to print float
CONFIG_NEWLIB_LIBC_FLOAT_PRINTF=y

And then include:

 #include "arm_math.h"

To make the functions available for use.

To keep space requirements low, some of the DSP functions might require setting additional Kconfig flags. You can browse those here: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/kconfig/index.html#!CMSIS_DSP

For examples on how to perform FFT using the DSP library, I found the following links:

Practical FFT on microcontrollers using CMSIS DSP

ARM CMSIS DSP FFT Library - Youtube

https://www.keil.com/pack/doc/CMSIS/DSP/html/arm_fft_bin_example_f32_8c-example.html (example from the library itself)

Hope that helps!

Best regards,

Raoul

[flau]

Thank you.  Will give that a try.