Stm32f4 MCU ADC sampling and FFT of ARM-DSP Library

The analog signal passes through ADC After sampling, it becomes a digital signal , Digital signals can be used FFT operation , It is easier to analyze the characteristics of the signal in the frequency domain . How will this be used STM32F4 In the process of ADC sampling , And make use of ARMDSP In the database FFT Algorithm to ADC The sampled values are subjected to fast Fourier transform .

I'm using STM32F407VG Single chip microcomputer , Because of the need ADC More sampling values （ Collected 4096 A little bit ）, So it's configured STM32 Of ADC and DMA, Use DMA take ADC It is more efficient to transfer the sampling value to memory . When configuring peripherals , Use APB2 Of the clock 2 Frequency division as ADCCLK,ADC The sampling time is 84 individual ADCCLK,Tconv（ Total conversion time ） = Sampling time +12 individual ADCCLK, Theoretically ADC The sampling frequency is about 4,375,00Hz. In order to ensure the integrity of the signal , According to Nyquist theorem, the sampling frequency needs to be greater than the highest frequency in the signal 2 times , Therefore, the signal frequency measured by the peripheral configuration method should not be greater than 218,750Hz. The peripheral configuration code is as follows ：

GPIO_InitTypeDef GPIO_InitStructure;
ADC_InitTypeDef ADC_InitStructure;
ADC_CommonInitTypeDef ADC_CommonInitStructure; 
DMA_InitTypeDef DMA_InitStructure;
NVIC_InitTypeDef  NVIC_InitStructure;	

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_DMA2|RCC_AHB1Periph_GPIOC,ENABLE);	
while(DMA_GetCmdStatus(DMA2_Stream0)!=DISABLE);				
RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE); 	
RCC_APB2PeriphResetCmd(RCC_APB2Periph_ADC1,ENABLE);  	
RCC_APB2PeriphResetCmd(RCC_APB2Periph_ADC1,DISABLE); 	
//init GPIO ADC1, channel 14
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_4;	
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;					
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;			
GPIO_Init(GPIOC, &GPIO_InitStructure);
	
DMA_InitStructure.DMA_Channel = DMA_Channel_0;
DMA_InitStructure.DMA_PeripheralBaseAddr = (unsigned int)&(ADC1->DR);
DMA_InitStructure.DMA_Memory0BaseAddr = (unsigned int)&(fft.ADC_ConvertedValue[0]);
DMA_InitStructure.DMA_DIR = DMA_DIR_PeripheralToMemory;
DMA_InitStructure.DMA_BufferSize = 4096;
DMA_InitStructure.DMA_PeripheralInc = DMA_PeripheralInc_Disable;
DMA_InitStructure.DMA_MemoryInc = DMA_MemoryInc_Enable;
DMA_InitStructure.DMA_PeripheralDataSize = DMA_PeripheralDataSize_HalfWord;
DMA_InitStructure.DMA_MemoryDataSize = DMA_MemoryDataSize_HalfWord;
DMA_InitStructure.DMA_Priority = DMA_Priority_High;
DMA_InitStructure.DMA_Mode = DMA_Mode_Normal;
DMA_InitStructure.DMA_FIFOMode = DMA_FIFOMode_Disable;
DMA_InitStructure.DMA_FIFOThreshold = DMA_FIFOThreshold_HalfFull;
DMA_InitStructure.DMA_MemoryBurst = DMA_MemoryBurst_Single;
DMA_InitStructure.DMA_PeripheralBurst = DMA_PeripheralBurst_Single;
DMA_Init(DMA2_Stream0,&DMA_InitStructure);

NVIC_InitStructure.NVIC_IRQChannel = DMA2_Stream0_IRQn;
NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
NVIC_Init(&NVIC_InitStructure);

DMA_ClearFlag(DMA2_Stream0,DMA_IT_TC);
DMA_ITConfig(DMA2_Stream0,DMA_IT_TC,ENABLE);// Enable data stream transmission completion interrupt 
DMA_Cmd(DMA2_Stream0,ENABLE);

ADC_CommonInitStructure.ADC_DMAAccessMode = ADC_DMAAccessMode_Disabled;
ADC_CommonInitStructure.ADC_Mode = ADC_Mode_Independent;
ADC_CommonInitStructure.ADC_Prescaler = ADC_Prescaler_Div2;//84M/2 = 42M
ADC_CommonInitStructure.ADC_TwoSamplingDelay = ADC_TwoSamplingDelay_20Cycles;
ADC_CommonInit(&ADC_CommonInitStructure);
	
ADC_InitStructure.ADC_Resolution = ADC_Resolution_12b;
ADC_InitStructure.ADC_ScanConvMode = DISABLE;
ADC_InitStructure.ADC_ContinuousConvMode = ENABLE;
ADC_InitStructure.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;
ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;
ADC_InitStructure.ADC_NbrOfConversion = 1;
ADC_Init(ADC1,&ADC_InitStructure);
ADC_Cmd(ADC1,ENABLE);
	
ADC_RegularChannelConfig(ADC1,ADC_Channel_14,1,ADC_SampleTime_84Cycles);// Conversion time 84 individual ADC cycle 
 
ADC_SoftwareStartConv(ADC1);
ADC_DMARequestAfterLastTransferCmd(ADC1,ENABLE);
ADC_DMACmd(ADC1,ENABLE);

Next , take ADC The sampling value of is converted to the corresponding voltage value , utilize DSP Library FFT Algorithm FFT operation , Calculate the amplitude frequency characteristics . here , I use base 4 floating-point FFT Algorithm , The base 4 Algorithm biki 2 Our algorithm is faster . The code is as follows ：

#define FFT_LENGTH 4096
void FFTTestTask(void *arg)
{
    OS_ERR err;
    CPU_TS ts;
    arm_cfft_radix4_instance_f32 scfft;
    int i = 0;
    unsigned char str[10];
	
    arm_cfft_radix4_init_f32(&scfft,FFT_LENGTH,0,1);//FFT initialization 
    while(1)
    {
        OSTaskSemPend(0,OS_OPT_PEND_BLOCKING,&ts,&err);// Waiting for transmission completion semaphore 
	for(i=0;i<FFT_LENGTH;i++)
	{
    	    fft.fft_input[2*i] = (float)fft.ADC_ConvertedValue[i]*3.3f/4096.0f;// The real part is ADC Sampling value 
	    fft.fft_input[2*i+1] = 0;// The imaginary part is 0
	}		
	arm_cfft_radix4_f32(&scfft,fft.fft_input);//FFT operation 
	arm_cmplx_mag_f32(fft.fft_input,fft.fft_output,FFT_LENGTH);// Calculate the modulus of each point 
	for(i=0;i<FFT_LENGTH;i++)
	{
            sprintf((char*)str,"%.2f\r\n",fft.fft_output[i]);
	    board.UART4Send(str,strlen((char*)str));// Print the data to the serial port assistant , Convenient for observation 
	    OSTimeDly(1,OS_OPT_TIME_DLY,&err);
	}
	OSTimeDly(500,OS_OPT_TIME_DLY,&err);
	board.ADC1_DMA2Enable();// Restart ADC Conversion and DMA transmission 
    }
}

In the experiments , I use FPGA and DAC Did DDS Signal generator , The generated waveform function is . The voltage signal is collected by the above method FFT operation , Finally using MATLAB Some amplitude frequency characteristic curves are drawn . The theoretical amplitude of DC component is 6758.4, actual value 7168.2; The theoretical amplitude of the fundamental component is 3379.2, actual value 3454.3.

Please correct the deficiencies .

The code download ： STM32F4 ADC sampling FFT Operation test code