Posted on March 10, 2018 at 21:40Hello,
I have a Nucleo-L476RG board and I'm trying to make a lowpass filter with the FIR function (using cmsis libraries) to filter the samples I get from the ADC in realtime.
Then I'd like to get the processed signal out through the DAC.
Both ADC and DAC work at a sampling frequency of 20khz, triggered by two (tim6 and tim7) timers. They use DMA.
FIR function is called every time the ADC ends a conversion.
I'm using arrays of 1 element as buffers, so the number of blocks of the FIR function is 1.
I can get a signal on the output, but it does not match what the input signal processed through the filter would be.
Thank you very much for your help. I hope my explanation is good enough.
Here is my code:
#include <math.h>
#include 'arm_math.h'
uint32_t adcValue[1];
uint32_t adcValue1[1];
int i;
float32_t signal_in = 0;
float32_t signal_out = 0;
#define TEST_LENGTH_SAMPLES 1
#define BLOCK_SIZE 1
#define NUM_TAPS 29
arm_fir_instance_f32 S;
static float32_t firStateF32[BLOCK_SIZE + NUM_TAPS - 1];
static float32_t firCoeffs[NUM_TAPS] = {-0.0018225230f, -0.0015879294f, +0.0000000000f, +0.0036977508f, +0.0080754303f,
+0.0085302217f, -0.0000000000f, -0.0173976984f, -0.0341458607f, -0.0333591565f,
+0.0000000000f, +0.0676308395f, +0.1522061835f, +0.2229246956f, +0.2504960933f,
+0.2229246956f, +0.1522061835f, +0.0676308395f, +0.0000000000f, -0.0333591565f,
-0.0341458607f, -0.0173976984f, -0.0000000000f, +0.0085302217f, +0.0080754303f,
+0.0036977508f, +0.0000000000f, -0.0015879294f, -0.0018225230f};
uint32_t blockSize = BLOCK_SIZE;
uint32_t numBlocks = TEST_LENGTH_SAMPLES/BLOCK_SIZE;
void SystemClock_Config(void);
int main(void)
{
HAL_Init();
/* Configure the system clock */
SystemClock_Config();
/* Initialize all configured peripherals */
MX_GPIO_Init();
MX_DMA_Init();
MX_DAC1_Init();
MX_TIM6_Init();
MX_ADC1_Init();
MX_TIM7_Init();
MX_ADC2_Init();
//Timers
HAL_TIM_Base_Start(&htim6);
HAL_TIM_Base_Start(&htim7);
//ADC Start
HAL_ADC_Start_DMA(&hadc1, adcValue, 1 );
//DAC Start
HAL_DAC_Start(&hdac1,DAC_CHANNEL_1);
HAL_DAC_Start_DMA(&hdac1, DAC_CHANNEL_1, (uint32_t*)adcValue1, 1, DAC_ALIGN_12B_R);
//FIR Init
arm_fir_init_f32(&S, NUM_TAPS, (float32_t *)&firCoeffs[0], (float32_t *)&firStateF32[0], blockSize);
/* Infinite loop */
while (1)
{
}
}
void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc)
{
if(hadc->Instance == ADC1)
{
signal_in = (float32_t)adcValue[0];
arm_fir_f32(&S, &signal_in, &signal_out, blockSize);
adcValue1[0] = (uint32_t)signal_out; //signal_out;
}
}
