PM0014 datasheet(39/46 Pages) STMICROELECTRONICS

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PM0014

Signal processing library functions

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6.3.3

fir_q31_q31_q31

fir_q31_q31_q31(struct Filter *FirPtr).

Description:

Real FIR filter of 32-bit fractional inputs, coefficients and outputs.

Argument:

FirPtr

Filter pointer.

Algorithm:

y(n) =

bi * x(n - i)

Note:

The delay line must be stored in DPRAM. Its size is 2*2*nb_coeff.

Before the first call to the function, the delay line must be initialized

to 0.

There is a saturation to 1 (respectively -1) if the computed output

sample is greater than 1 (respectively lower than -1).

Example of the use for fir_q31_q31_q31:

#define FirNumberCoeffs NumberOfCoefficients

#define NbOutput NumberOfOutputSamples

iram short Delayline[FirNumberCoeffs];

iram short Coeff[2*FirNumberCoeffs];//coef are 32-bit wide

void main ()

{

// Data definition

short Input[2*NbOutput];//Input are 32-bit wide

short Out[2* NbOutput];//Output are 32-bit wide

// Here should be the coef[] and input[] initialization.

See the Test part...

// Declare a filter structure

struct Filter *Filt;

// Initialisation of filt

Filt.NumberCoeffs = FirNumberCoeffs;

Filt.NumberOutputSamples = NbOutput;

Filt.CoeffPtr = Coeff;

Filt.InputPtr = Input;

Filt.OutputPtr = Out;

Filt.DelayLinePtr = Delayline;

//Filter processing

fir_q31_q31_q31(&Filt);

}

Coefficients must be stored in memory as follows:

addr

Filt.CoeffPtr

----> a0 lsb

addr

Filt.CoeffPtr + 2 ----> a0

msb

...

addr

Filt.CoeffPtr + 4 *(FirNumberCoeffs -2)---->

aFirNumberCoeffs-1 msb

Inputs and Outputs are stored in memory as follows:

addr

Filt.InputPtr

----> x0 lsb

addr

Filt.InputPtr + 2 ----> x0

msb

...

addr

Filt.Input + 4 *(NbOutput -2)----> aNbOutput-1 msb

addr

Filt.OutputPtr

----> y0 lsb

addr

Filt.OutputPtr + 2 ----> y0

msb

...

addr

Filt.OutputPtr + 4 *(NbOutput -2)----> aNbOutput-1 msb

nbcoeff

–



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