IIR ARMA 16-bit filter

UM0304

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IIR ARMA 16-bit filter

2.1

Description

The IIR filter function performs an ARMA filter with 4 auto-regressive filter coefficients and 5

moving-average filter coefficients respectively for ny output samples. This is a 16-bit fixed-

point implementation. Reference [1] may be used to explore more about IIR filters.

2.2

Function

void iirarma_arm9e(void *y, void *x, short *h2, short *h1, int ny);

2.3

Arguments and variables

●

Output array vector y[ny+4] (used in actual computation. first four elements must have

the previous outputs. Thus the first output starts y[4] when ny = 0)

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Input array vector x[ny+4]

●

Moving-average filter coefficients vector h2[5]

●

Auto-regressive filter coefficients h1[5] and h1[0] are not used

●

Number of output samples ny is a multiple of 4 and must be

≥ 8

2.3.1

Calling the function from C

Set the arguments and variables as appropriate in C main program and call the function.

In the STR91x DSPLIB this is set in the 91x_dsp.h header file.

2.3.2

Calling the function from assembly

Use the following registers equivalent to arguments/variables.

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R0 to the address of output vector y[]

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R1 to the address of input vector x[]

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R2 to the address of coefficient vector h2[]

●

R3 to the address of coefficient vector h1[]

●

R12 to the address of ny

Then use the BL instruction to call the function.