overflow with arm_biquad_cascade_df2T_f32 function

Posted on June 25, 2013 at 14:40

Hi,

I try to implement a IIR filter with the ''

arm_biquad_cascade_df2T_f32

'' function from the CMIS dsp libraries and I encountered a problem: my output datas and my pstate table are overflowed after few iterations. I generated my coefficients with fdatool from matlab. They are stored in the followed order:

{b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}

float32_t iir_coeff[30] = {
1, -0.0249943904456238, 0.999999999999993, -1.77729633861929, 0.845140679514385,
1, -1.42288228590609, 0.999999999999998, -1.72245970919624, 0.896574493119215,
1, -1.99973299802181, 1, -1.91581723732986, 0.929183550605981,
1, -1.5986745646875, 1, -1.72677706239042, 0.969582040573283,
1, -1.99845599796938, 0.999999999999999, -1.97568100711438, 0.981035519941801,
1, -1.99766610993993, 1, -1.99201600960503, 0.995968747765197
};

I don't know how to incorporate the ''Scale factors''. I try to add it to my coeff table as follow but it dosn't work.

float32_t iir_coeff[35] = {
0.001843832549177, 0, 0, 0, 0,
1, -0.0249943904456238, 0.999999999999993, -1.77729633861929, 0.845140679514385,
1, -1.42288228590609, 0.999999999999998, -1.72245970919624, 0.896574493119215,
1, -1.99973299802181, 1, -1.91581723732986, 0.929183550605981,
1, -1.5986745646875, 1, -1.72677706239042, 0.969582040573283,
1, -1.99845599796938, 0.999999999999999, -1.97568100711438, 0.981035519941801,
1, -1.99766610993993, 1, -1.99201600960503, 0.995968747765197
};

Here a part of my code:

#define NUM_STAGE 7 // if I don't incorporate the ''Scale factors'' NUM_STAGE = 6 

static
float32_t iirStateF32X[2*NUM_STAGE];
arm_biquad_cascade_df2T_instance_f32 SX;
int
main(
void
)
{ 
arm_biquad_cascade_df2T_init_f32(&SX, NUM_STAGE, (float32_t *)&iir_coeff[0], &iirStateF32X[0]);
...
// in the interruption:
float32_t *inputF32X, *outputF32X
inputF32X = &temp_buffer[0];
outputF32X = &AccBufferX_filter[0]; 
arm_biquad_cascade_df2T_f32(&SX, inputF32X, outputF32X, FILTER_BUFFER_SIZE);

This code works with the fir functions. Does someone know where the problem is ? Thanks.