Project Ne10
An open, optimized software library for the ARM architecture.

Functions  
ne10_result_t  ne10_fir_interpolate_init_float (ne10_fir_interpolate_instance_f32_t *S, ne10_uint8_t L, ne10_uint16_t numTaps, ne10_float32_t *pCoeffs, ne10_float32_t *pState, ne10_uint32_t blockSize) 
Initialization function for the floatingpoint FIR interpolator. More...  
void  ne10_fir_interpolate_float_c (const ne10_fir_interpolate_instance_f32_t *S, ne10_float32_t *pSrc, ne10_float32_t *pDst, ne10_uint32_t blockSize) 
Specific implementation of ne10_fir_interpolate_float using plain C. More...  
void  ne10_fir_interpolate_float_neon (const ne10_fir_interpolate_instance_f32_t *S, ne10_float32_t *pSrc, ne10_float32_t *pDst, ne10_uint32_t blockSize) asm("ne10_fir_interpolate_float_neon") 
Specific implementation of ne10_fir_interpolate_float using NEON SIMD capabilities. More...  
Variables  
void(*  ne10_fir_interpolate_float )(const ne10_fir_interpolate_instance_f32_t *S, ne10_float32_t *pSrc, ne10_float32_t *pDst, ne10_uint32_t blockSize) 
Processing function for the floatingpoint FIR interpolator. More...  
L
, the signal should be filtered by a lowpass filter with a normalized cutoff frequency of 1/L
in order to eliminate high frequency copies of the spectrum. The user of the function is responsible for providing the filter coefficients.The FIR interpolator functions provided in the CMSIS DSP Library combine the upsampler and FIR filter in an efficient manner. The upsampler inserts L1
zeros between each sample. Instead of multiplying by these zero values, the FIR filter is designed to skip them. This leads to an efficient implementation without any wasted effort. The functions operate on blocks of input and output data. pSrc
points to an array of blockSize
input values and pDst
points to an array of blockSize*L
output values.
The library provides functions for floatingpoint data types.
y[n] = b[0] * x[n] + b[L] * x[n1] + ... + b[L*(phaseLength1)] * x[nphaseLength+1] y[n+1] = b[1] * x[n] + b[L+1] * x[n1] + ... + b[L*(phaseLength1)+1] * x[nphaseLength+1] ... y[n+(L1)] = b[L1] * x[n] + b[2*L1] * x[n1] + ....+ b[L*(phaseLength1)+(L1)] * x[nphaseLength+1]This approach is more efficient than straightforward upsamplethenfilter algorithms. With this method the computation is reduced by a factor of
1/L
when compared to using a standard FIR filter. pCoeffs
points to a coefficient array of size numTaps
. numTaps
must be a multiple of the interpolation factor L
and this is checked by the initialization functions. Internally, the function divides the FIR filter's impulse response into shorter filters of length phaseLength=numTaps/L
. Coefficients are stored in time reversed order. {b[numTaps1], b[numTaps2], b[N2], ..., b[1], b[0]}
pState
points to a state array of size blockSize + phaseLength  1
. Samples in the state buffer are stored in the order: {x[nphaseLength+1], x[nphaseLength], x[nphaseLength1], x[nphaseLength2]....x[0], x[1], ..., x[blockSize1]}The state variables are updated after each block of data is processed, the coefficients are untouched.
ne10_fir_interpolate_instance_f32_t S = {L, phaseLength, pCoeffs, pState};where
L
is the interpolation factor; phaseLength=numTaps/L
is the length of each of the shorter FIR filters used internally, pCoeffs
is the address of the coefficient buffer; pState
is the address of the state buffer. Be sure to set the values in the state buffer to zeros when doing static initialization.void ne10_fir_interpolate_float_c  (  const ne10_fir_interpolate_instance_f32_t *  S, 
ne10_float32_t *  pSrc,  
ne10_float32_t *  pDst,  
ne10_uint32_t  blockSize  
) 
Specific implementation of ne10_fir_interpolate_float using plain C.
Definition at line 679 of file NE10_fir.c.
void ne10_fir_interpolate_float_neon  (  const ne10_fir_interpolate_instance_f32_t *  S, 
ne10_float32_t *  pSrc,  
ne10_float32_t *  pDst,  
ne10_uint32_t  blockSize  
) 
Specific implementation of ne10_fir_interpolate_float using NEON SIMD capabilities.
ne10_result_t ne10_fir_interpolate_init_float  (  ne10_fir_interpolate_instance_f32_t *  S, 
ne10_uint8_t  L,  
ne10_uint16_t  numTaps,  
ne10_float32_t *  pCoeffs,  
ne10_float32_t *  pState,  
ne10_uint32_t  blockSize  
) 
Initialization function for the floatingpoint FIR interpolator.
[in,out]  *S  points to an instance of the floatingpoint FIR interpolator structure. 
[in]  L  upsample factor. 
[in]  numTaps  number of filter coefficients in the filter. 
[in]  *pCoeffs  points to the filter coefficient buffer. 
[in]  *pState  points to the state buffer. 
[in]  blockSize  number of input samples to process per call. 
numTaps
is not a multiple of the interpolation factor L
.Description:
pCoeffs
points to the array of filter coefficients stored in time reversed order: {b[numTaps1], b[numTaps2], b[numTaps2], ..., b[1], b[0]}The length of the filter
numTaps
must be a multiple of the interpolation factor L
. pState
points to the array of state variables. pState
is of length (numTaps/L)+blockSize1
words where blockSize
is the number of input samples processed by each call to arm_fir_interpolate_f32()
. Definition at line 164 of file NE10_fir_init.c.
void(* ne10_fir_interpolate_float) (const ne10_fir_interpolate_instance_f32_t *S, ne10_float32_t *pSrc, ne10_float32_t *pDst, ne10_uint32_t blockSize) 
Processing function for the floatingpoint FIR interpolator.
[in]  *S  points to an instance of the floatingpoint FIR interpolator structure. 
[in]  *pSrc  points to the block of input data. 
[out]  *pDst  points to the block of output data. 
[in]  blockSize  number of input samples to process per call. 
Points to ne10_fir_interpolate_float_c or ne10_fir_interpolate_float_neon.
Definition at line 174 of file NE10_init_dsp.c.