RM0020 datasheet(48/69 Pages) STMICROELECTRONICS

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Function API

RM0020

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Arguments:

Description:

Computes the second-order IIR filter on float data. The input samples are stored in

the array x, output samples are written to the array y.

Algorithm:

Equation 40

for each n from 0 to N-1

Performance: See Section 7 and Table 56.

Example 25. iir_float_2nd

#include "libdsp2.h"

/* #pragma and ALIGN macros used to align to 8 bytes */

#ifdef __ghs__

#pragma alignvar (8)

#endif

ALIGN_DCC(8)

float x[256/*+4*/] ALIGN_MWERKS(8); /* +4 to ensure there are 16

bytes of readable memory behind x */

#ifdef __ghs__

#pragma alignvar (8)

#endif

ALIGN_DCC(8)

float y [256] ALIGN_MWERKS(8);

#ifdef __ghs__

#pragma alignvar (8)

#endif

ALIGN_DCC(8)

float s[4] ALIGN_MWERKS(8) = {0,0,0,0};

float c[5]

{0.3115387742F,0.6230775485F,0.3115387742F,0.0736238464F,0.17253125

05F};

Table 25.

iir_float_2nd 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. 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)

array of filter coefficients, c[5] = {b0, b1, b2, a1, a2}

in/out

array of previous input and output values (state vector), s[4] = {x(-2),

x(-1), y(-2), y(-1)}



xn

 b1

xn 1

–

 b2

xn 2

–

 a1

yn 1

–



–

yn 2

–



–

RM0020 Datasheet(PDF) 48 Page - STMicroelectronics

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