I want to read ADC data to float buffer in STM32L4 (with FPU)
I read ADC with DMA. When the buffer is full, then callback set flag and perform FFT calculations. To do this I need ADC data stored in a float buffer. Here is a problem, values of this are for example 1.51059974e-042. When I get value (adc_val = HAL_ADC_GetValue (&hadc1);) (uint32_t) data is good. Casting to float has the same result. When I calculate fft values are equal 0. I done some test with signal stored in vector and function for fft is proper, so problem is in ADC reading.
ADC.c
oid MX_ADC1_Init(void)
{
/* USER CODE BEGIN ADC1_Init 0 */
/* USER CODE END ADC1_Init 0 */
ADC_ChannelConfTypeDef sConfig = {0};
/* USER CODE BEGIN ADC1_Init 1 */
/* USER CODE END ADC1_Init 1 */
/** Common config
*/
hadc1.Instance = ADC1;
hadc1.Init.ClockPrescaler = ADC_CLOCK_ASYNC_DIV2;
hadc1.Init.Resolution = ADC_RESOLUTION_12B;
hadc1.Init.DataAlign = ADC_DATAALIGN_RIGHT;
hadc1.Init.ScanConvMode = ADC_SCAN_DISABLE;
hadc1.Init.EOCSelection = ADC_EOC_SINGLE_CONV;
hadc1.Init.LowPowerAutoWait = DISABLE;
hadc1.Init.ContinuousConvMode = DISABLE;
hadc1.Init.NbrOfConversion = 1;
hadc1.Init.DiscontinuousConvMode = DISABLE;
hadc1.Init.ExternalTrigConv = ADC_SOFTWARE_START;
hadc1.Init.ExternalTrigConvEdge = ADC_EXTERNALTRIGCONVEDGE_NONE;
hadc1.Init.DMAContinuousRequests = ENABLE;
hadc1.Init.Overrun = ADC_OVR_DATA_PRESERVED;
hadc1.Init.OversamplingMode = DISABLE;
hadc1.Init.DFSDMConfig = ADC_DFSDM_MODE_ENABLE;
if (HAL_ADC_Init(&hadc1) != HAL_OK)
{
Error_Handler();
}
/** Configure Regular Channel
*/
sConfig.Channel = ADC_CHANNEL_8;
sConfig.Rank = ADC_REGULAR_RANK_1;
sConfig.SamplingTime = ADC_SAMPLETIME_247CYCLES_5;
sConfig.SingleDiff = ADC_SINGLE_ENDED;
sConfig.OffsetNumber = ADC_OFFSET_NONE;
sConfig.Offset = 0;
if (HAL_ADC_ConfigChannel(&hadc1, &sConfig) != HAL_OK)
{
Error_Handler();
}
/* USER CODE BEGIN ADC1_Init 2 */
/* USER CODE END ADC1_Init 2 */
}
void HAL_ADC_MspInit(ADC_HandleTypeDef* adcHandle)
{
GPIO_InitTypeDef GPIO_InitStruct = {0};
RCC_PeriphCLKInitTypeDef PeriphClkInit = {0};
if(adcHandle->Instance==ADC1)
{
/* USER CODE BEGIN ADC1_MspInit 0 */
/* USER CODE END ADC1_MspInit 0 */
/** Initializes the peripherals clock
*/
PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_ADC;
PeriphClkInit.AdcClockSelection = RCC_ADCCLKSOURCE_PLLSAI1;
PeriphClkInit.PLLSAI1.PLLSAI1Source = RCC_PLLSOURCE_HSI;
PeriphClkInit.PLLSAI1.PLLSAI1M = 1;
PeriphClkInit.PLLSAI1.PLLSAI1N = 12;
PeriphClkInit.PLLSAI1.PLLSAI1P = RCC_PLLP_DIV2;
PeriphClkInit.PLLSAI1.PLLSAI1Q = RCC_PLLQ_DIV2;
PeriphClkInit.PLLSAI1.PLLSAI1R = RCC_PLLR_DIV2;
PeriphClkInit.PLLSAI1.PLLSAI1ClockOut = RCC_PLLSAI1_ADC1CLK;
if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit) != HAL_OK)
{
Error_Handler();
}
/* ADC1 clock enable */
__HAL_RCC_ADC_CLK_ENABLE();
__HAL_RCC_GPIOA_CLK_ENABLE();
/**ADC1 GPIO Configuration
PA3 ------> ADC1_IN8
*/
GPIO_InitStruct.Pin = GPIO_PIN_3;
GPIO_InitStruct.Mode = GPIO_MODE_ANALOG_ADC_CONTROL;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOA, &GPIO_InitStruct);
/* ADC1 DMA Init */
/* ADC1 Init */
hdma_adc1.Instance = DMA1_Channel1;
hdma_adc1.Init.Request = DMA_REQUEST_ADC1;
hdma_adc1.Init.Direction = DMA_PERIPH_TO_MEMORY;
hdma_adc1.Init.PeriphInc = DMA_PINC_DISABLE;
hdma_adc1.Init.MemInc = DMA_MINC_ENABLE;
hdma_adc1.Init.PeriphDataAlignment = DMA_PDATAALIGN_WORD;
hdma_adc1.Init.MemDataAlignment = DMA_MDATAALIGN_WORD;
hdma_adc1.Init.Mode = DMA_CIRCULAR;
hdma_adc1.Init.Priority = DMA_PRIORITY_VERY_HIGH;
if (HAL_DMA_Init(&hdma_adc1) != HAL_OK)
{
Error_Handler();
}
__HAL_LINKDMA(adcHandle,DMA_Handle,hdma_adc1);
/* USER CODE BEGIN ADC1_MspInit 1 */
/* USER CODE END ADC1_MspInit 1 */
}
}
void HAL_ADC_MspDeInit(ADC_HandleTypeDef* adcHandle)
{
if(adcHandle->Instance==ADC1)
{
/* USER CODE BEGIN ADC1_MspDeInit 0 */
/* USER CODE END ADC1_MspDeInit 0 */
/* Peripheral clock disable */
__HAL_RCC_ADC_CLK_DISABLE();
/**ADC1 GPIO Configuration
PA3 ------> ADC1_IN8
*/
HAL_GPIO_DeInit(GPIOA, GPIO_PIN_3);
/* ADC1 DMA DeInit */
HAL_DMA_DeInit(adcHandle->DMA_Handle);
/* USER CODE BEGIN ADC1_MspDeInit 1 */
/* USER CODE END ADC1_MspDeInit 1 */
}
}
so problem is in ADC reading
The problem is not with the ADC - the ADC produces integer sample values, and the DMA just copies the ADC DR to successive memory locations. It cannot do the conversion either.
The problem will be in how or where you performed the cast. A safer solution would be on occurrence of the DMA transfer interrupt and convert the data to a float buffer in an iteration.
Bear in mind that simply casting an integer to a float will simply give you a float representation of the same magnitude. So for example a value 2000 simply becomes 2000.0f. That may not be what your FFT expects. Rather the input might be
require normalisation : 1.0 > s > -1.0 or 1.0 > s > 0 if not "signed".
For signed samples you would need to subtract the DC offset from the incoming signal, which may not be at the mid-point of the ADC range, and may in any case be variable or non-deterministic. To deal with that you might need to apply a DC-blocking High-Pass filter (with a very low cut-off frequency).
In the end you cannot operate on the DMA buffer data directly in your FFT if your FFT expects float data. Either transform the data to a form the FFT requires (a simple cast won't cut it) or use an integer FFT function.