For detailed example samples, refer to the following link: http://www.nuvoton.com/hq/resource-download.jsp?tp_GUID=EC0120160922110158
Enable the DSP function:

1. In Keil, select Target Options, switch to the C/C ++ window and then enter ARM_MATH_CM4 = 1 in the Define text field.

2. In the Library section, add arm_cortexM4lf_math.lib at \Library\CMSIS\Lib\ARM.

3. Include arm_math.h to the main function. After that, the DSP library can be called in the main function.

First, the even-numbers in the data format to be calculated are real numbers and the odd-numbers are imaginary numbers, e.g. 1+0.5i, 2+4i, 3+2i=>testinput={1, 0.5, 2, 4, 3, 2}, FFTsize=3.
Then, call the function arm_cfft_radix4_init_f32(&S, fftSize, ifftFlag, doBitReverse) to do the initial settings for Fast Fourier operation, including the number of operations, the need for fast Fourier or inverse fast Fourier transform.
Call the function arm_cfft_radix4_f32(&S, testinput) for fast Fourier transform operations, and the results are stored in the array testinput, where the results are complex.
Take the absolute value of the complex number to get the frequency intensity, and output the results to Output. Since the result is left-right symmetry, the amount of computation is fftSize/2, arm_cmplx_mag_f32(testinput, Output, fftSize/2).
Get the frequency intensity as y-axis data, and then calculate the x-axis for each frequency mode as

The calculation results are shown as follows. The strongest frequency of the signal can be about 1 kHz.

Products:	Microcontrollers ,Arm Cortex-M4 MCUs ,M451 Base Series ,M451M Series ,M452 USB Series ,M453 CAN Series ,M4TK Touch Key Series ,NUC442/472 Series ,NUC505 Series
Applications:
Function:	Peripherals,ARM,DSP,FPU,Connectivity,I2C

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How to use the DSP function in the NuMicro® M4 series for spectrum analysis? Issue Date：2017-02-02

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