RM0020 datasheet(49/69 Pages) STMICROELECTRONICS

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RM0020

Function API

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unsigned short N;

void main(void)

{

/* filter the samples in x with second-order IIR filter, */

/* write result into y */

N = 256;

iir_float_2nd(N, x, y, c, s);

}

6.26

iir_float_casc - cascade of float second-order IIR filters

Function call:

#define iir_float_casc

iir_float_casc_c

void iir_float_casc_c(unsigned short N, float *x, float *y, float

*c,

float *s, unsigned short m);

Arguments:

Description:

Computes the cascade of second-order IIR filters on float data. The input samples

are stored in the array x, output samples are written to the array y. The function calls

the iir_float_2nd function for each second-order IIR filter in the cascade.

Algorithm:

The filter equation for the i-order IIR filter (i = 2*m):

Table 26.

iir_float_casc arguments(1)

The arrays x,y,s must be double-word aligned, the array c must be word aligned (implicit alignment

of float data). There must be 16 bytes of readable memory behind the array x and y. There are

returned new values of x(-2), x(-1), y(-2), y(-1) in the array s to be ready for next function call.

Nin

number of input and output samples (N must be multiple of 4, must be

>= 8)

array of input samples of length N, x(0) x(1) ... x(N-1)

out

array of output samples of length N, y(0) y(1) ... y(N-1)

cin

array of filter coefficients for each second-order IIR filter, c[m*5] =

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

...,

bm0, bm1, bm2, am1, am2}

in/out

array of previous input and output values (state vector), s[m*4] =

{x1(-2), x1(-1), y1(-2), y1(-1), x2(-2), x2(-1), y2(-2), y2(-1),

...,

xm(-2), xm(-1), ym(-2), ym(-1)}

number of second-order IIR filters in the cascade

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