Error with arm_fir_f32()

[ASpie.11]

Hi,

i'm using the arm_fir_f32() funktion to filter a real time input signal.

My problem is, that the funktion return '-nan' for each input.

#include "foc.h"

#include "tim.h"

#include "adc.h"

#include "debug.h"

#include "arm_math.h"

/* FIR-FILTER */

#define BLOCK_SIZE 8

#define NUM_TAPS 10

uint16_t blocksize = BLOCK_SIZE;

arm_fir_instance_f32 S;

static float32_t firStateF32[BLOCK_SIZE + NUM_TAPS -1];

const float32_t firCoeffs32[NUM_TAPS] = {

 0.1f, 0.1f, 0.1f, 0.1f, 0.1f, 0.1f, 0.1f, 0.1f, 0.1f, 0.1f,

};

float32_t in[8]={0, 0, 0, 0, 0, 0, 0, 0};

float32_t out[8]={0, 0, 0, 0, 0, 0, 0, 0};

/* Init FIR-Filter */

arm_fir_init_f32(&S, NUM_TAPS, (float32_t *)&firCoeffs32[0], &firStateF32[0], blocksize);

/* This funktion is called after the adc-conversion is finished (20000Hz) */

void FOCLOOP(void)

{

   Get_Angle_rad(ADC_Value[3], &theta_rad_mech[0]);

   Convert_Angle_rad(&theta_rad_mech[0], &theta_rad_el[0], motor_1.PPZ);

   theta_grad_el = radtograd(theta_rad_el[0]);

   CalcOmega(&theta_rad_mech[0], &omega_el[0], freq);

   for(int i = BLOCK_SIZE; i>=1; i--) {

      in[i] = in[i-1];

   }

   in[0] = omega_el[0];

   arm_fir_f32(&S, &in[0], &out[0], blocksize);

}

[Tesla DeLorean]

Perhaps find and review others examples for usage?

STM32Cube_FW_F4_V1.21.0\Drivers\CMSIS\DSP_Lib\Examples\arm_signal_converge_example\ARM\arm_signal_converge_example_f32.c

[AvaTar]

The float datatype has a limited precision of only 24 bytes, which makes "divisions by almost zero" much more probable.

I suggest to single-step through your code, and check where the problem occurs. You might be able to tweek filter coefficients and input data (angles ?) to avoid the problem.

[Piranha]

To not confuse some newbies, I'll correct - in C language float datatype has a size of 32 bits, but precision of 24 bits (not bytes). 🙂