Embedded Software and Motor Control Libraries for PXR40xx

Function GDFLIB_FilterIIR2_F16
freq_bot = 400;
freq_top = 625;
T_sampling = 100e-6;
[b,a]= butter(1,[freq_bot freq_top]*T_sampling *2, 'bandpass');
sys =tf(b,a,T_sampling);
bode(sys,[freq_bot:1:freq_top]*2*pi)
f16B0 = b(1)/8;
f16B1 = b(2)/8;
f16B2 = b(3)/8;
f16A1 = a(2)/8;
f16A2 = a(3)/8;
disp (' Coefficients for GDFLIB_FilterIIR2 function :');
disp ([ 'f16B0 = FRAC16(' num2str( f16B0 ) ')']);
disp ([ 'f16B1 = FRAC16(' num2str( f16B1 ) ')']);
disp ([ 'f16B2 = FRAC16(' num2str( f16B2 ) ')']);
disp ([ 'f16A1 = FRAC16(' num2str( f16A1 ) ')']);
disp ([ 'f16A2 = FRAC16(' num2str( f16A2 ) ')']);
Note
The filter delay line includes four delay buffers which should
be reset after filter initialization. This can be done by assigning
to the filter instance a
GDFLIB_FILTER_IIR2_DEFAULT_F16 macro during
instance declaration or by calling the
GDFLIB_FilterIIR2Init_F16 function.
CAUTION
Because of fixed point implementation, and to avoid overflow
during the calculation of the GDFLIB_FilterIIR2_F16 function,
filter coefficients must be divided by eight. Function output is
internally multiplied by eight to correct the coefficient scaling.
4.16.5 Re-entrancy
The function is re-entrant.
4.16.6 Code Example
#include "gdflib.h"
tFrac16 f16In;
tFrac16 f16Out;
GDFLIB_FILTER_IIR2_T_F16 f16trMyIIR2 = GDFLIB_FILTER_IIR2_DEFAULT_F16;
void main(void)
{
// input value = 0.25
f16In = FRAC16 (0.25);
// filter coefficients (BPF 400-625Hz, Ts=100e-6)
Embedded Software and Motor Control Libraries for PXR40xx, Rev. 1.0
190 Freescale Semiconductor, Inc.