MSP430FR6889: Use of "DSPLib.h" library to measure FFT

Part Number: MSP430FR6889

Hello,

I am using MSP430 and BMI160 in a project. I am using the BMI160 accelerometer to measure vibration. The idea is to use the DSPLib's FFT function to determine the dominant frequency in a vibration event. Based on my current understanding of FFT analysis, I realized that I need the number of samples, which should be 2^n data points, and I will also need the sampling frequency. When I am using this function:

msp_status msp_fft_fixed_q15	(	const msp_fft_q15_params * 	params,
int16_t * 	src 
)	

I am passing the "params" and "src" parameters (source):

params: Pointer to the real FFT parameter structure. 
src: Pointer to the real data array to perform the FFT on.

And I think this is the parameter structure (source: DSPLib_transform.h):

typedef struct msp_fft_q15_params {
    //! \details
    //! Length of the source data, must be a power of two.
    uint16_t length;
    //! \details
    //! Perform bit-reversal of the input before transformation. This step is
    //! mandatory, this parameter only exists for applications that might handle
    //! bit reversal when storing the data samples to memory. If not this needs
    //! to be set to true.
    bool bitReverse;
    //! \details
    //! Pointer to the twiddle coefficient table with size greater than or equal
    //! to the source length. When using LEA this can be a NULL pointer.
    const _q15 *twiddleTable;
} msp_fft_q15_params;

When I am sending the "scr" parameter, I am sending the actual data points and their amplitude. So, for example, if I am taking 1024 samples from the z-axis of the accelerometer, I am storing the amplitudes of 1024 consecutive samples in that array.

But I am not sure how I am passing the sampling frequency of the samples to the FFT function. I would really appreciate it if someone could explain how this FFT function is doing the FFT analysis.

Thank you.