Embedded Software and Motor Control Libraries for PXR40xx

Equation GDFLIB_FilterFIR_Eq1
where: x[n] is the input signal, y[n] is the output signal, h i are the filter coefficients, and
N is the filter order. It should be noted, that the number of taps of the filter is N + 1 in
this case.
The function assumes that the filter order is at least one, which is equivalent to two taps.
The filter also cannot contain more than 0xffffffff(hexadecimal) taps, which is equivalent
to the order of 0xfffffffe (hexadecimal).
The input values are recorded by the function in the provided state structure in a circular
buffer, pointed to by the state structure member pState->pInBuf. The buffer index is
stored in pState->u32Idx, which points to the buffer element where a new input signal
sample will be stored.
The filter coefficients are stored in the parameter structure, in the structure member
pParam->pCoefBuf.
The first call to the function must be preceded by an initialization, which can be made
through the GDFLIB_FilterFIRInit_FLT function. The GDFLIB_FilterFIRInit_FLT and
then the GDFLIB_FilterFIR_FLT functions should be called with the same parameters.
4.6.5 Re-entrancy
The function is re-entrant only if the calling code is provided with a distinct instance of
the structure pointed to by pState.
Note
From the performance point of view, the function is designed to
work with filters with a larger number of taps (equal order + 1).
As a rule of thumb, if the number of taps is lower than 5, a
different algorithm should be considered.
4.6.6 Code Example
#include "gdflib.h"
#define FIR_NUMTAPS 16
#define FIR_NUMTAPS_MAX 64
#define FIR_ORDER (FIR_NUMTAPS - 1)
Embedded Software and Motor Control Libraries for PXR40xx, Rev. 1.0
Chapter 4 API References
Freescale Semiconductor, Inc. 165