RM0020 datasheet(52/69 Pages) STMICROELECTRONICS

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Function API

RM0020

52/69

short x[256/*+2*/] ALIGN_MWERKS(4); /* +2 to ensure there are 4

bytes of readable memory behind x */

#ifdef __ghs__

#pragma alignvar (4)

#endif

ALIGN_DCC(4)

short y[256] ALIGN_MWERKS(4);

#ifdef __ghs__

#pragma alignvar (4)

#endif

ALIGN_DCC(4)

short s[2] ALIGN_MWERKS(4) = {0,0};

short c[3]

= {16899,16899,1030};

unsigned short N;

void main(void)

{

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

/* write result into y */

N = 256;

iir_frac16_1st(N, x, y, c, s);

}

6.28

iir_frac16_2nd - frac16 second-order IIR filter

Function call:

void iir_frac16_2nd(unsigned short N, short *x, short *y, short *c,

short *s);

Arguments:

Description:

Computes the second-order IIR filter on frac16 data. The input samples are stored in

the array x, output samples are written to the array y. There is used the arithmetic with

saturation so the output will never overflow.

Table 28.

iir_frac16_2nd arguments(1)

The x,y,c,s data are in fractional 16-bit format in range -1 to 1. The arrays x,y,s must be word

aligned, the array c must be half-word aligned (implicit alignment of short data). There must be 4

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.

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

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}

sin/out

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

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

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