RM0020 datasheet(45/69 Pages) STMICROELECTRONICS

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RM0020

Function API

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ntaps = 33;

fir_float(N, ntaps, x, y, hr);

}

6.23

fir_frac16 - frac16 FIR filter

Function call:

void fir_frac16(unsigned short N, unsigned short ntaps, short *x,

short *y, short *h);

Arguments:

Description:

Computes the real FIR filter on frac16 data. The input samples are stored in the array

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

Algorithm:

Equation 37

for each n from 0 to N-1

Note: The coefficients stored in the array h must be scaled to prevent a saturation, i.e. the

sum of the absolute values of all coefficients must be lower than 215:

Equation 38

The filter coefficients must be stored in reversed order.

Performance: See Section 7 and Table 54.

Example 23. fir_frac16

#include "libdsp2.h"

/* #pragma and ALIGN macros used to align to 4 bytes */

Table 23.

fir_frac16 arguments(1)

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

the array h must be half-word aligned (implicit alignment of short data). There must be 2 bytes of

readable memory behind the array h and 4 bytes of readable memory behind the array x.

length of output array y (must be multiple of 2)

ntaps

number of filter coefficients (must be >= 4)

xin

array of input samples of length N+ntaps-1, x(-ntaps+1) x(-ntaps+2)

... x(0) x(1) ... x(N-1)

out

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

hin

array of filter coefficients stored in reversed order, h(ntaps-1) ... h(1)

h(0)



 xn k

–





ntaps

–





ntaps

–





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