CMSISDSP
Version 1.5.2
CMSIS DSP Software Library

Functions  
void  arm_fir_interpolate_f32 (const arm_fir_interpolate_instance_f32 *S, float32_t *pSrc, float32_t *pDst, uint32_t blockSize) 
Processing function for the floatingpoint FIR interpolator. More...  
arm_status  arm_fir_interpolate_init_f32 (arm_fir_interpolate_instance_f32 *S, uint8_t L, uint16_t numTaps, float32_t *pCoeffs, float32_t *pState, uint32_t blockSize) 
Initialization function for the floatingpoint FIR interpolator. More...  
arm_status  arm_fir_interpolate_init_q15 (arm_fir_interpolate_instance_q15 *S, uint8_t L, uint16_t numTaps, q15_t *pCoeffs, q15_t *pState, uint32_t blockSize) 
Initialization function for the Q15 FIR interpolator. More...  
arm_status  arm_fir_interpolate_init_q31 (arm_fir_interpolate_instance_q31 *S, uint8_t L, uint16_t numTaps, q31_t *pCoeffs, q31_t *pState, uint32_t blockSize) 
Initialization function for the Q31 FIR interpolator. More...  
void  arm_fir_interpolate_q15 (const arm_fir_interpolate_instance_q15 *S, q15_t *pSrc, q15_t *pDst, uint32_t blockSize) 
Processing function for the Q15 FIR interpolator. More...  
void  arm_fir_interpolate_q31 (const arm_fir_interpolate_instance_q31 *S, q31_t *pSrc, q31_t *pDst, uint32_t blockSize) 
Processing function for the Q31 FIR interpolator. More...  
These functions combine an upsampler (zero stuffer) and an FIR filter. They are used in multirate systems for increasing the sample rate of a signal without introducing high frequency images. Conceptually, the functions are equivalent to the block diagram below:
After upsampling by a factor of 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 separate functions for Q15, Q31, and 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.
arm_fir_interpolate_instance_f32 S = {L, phaseLength, pCoeffs, pState}; arm_fir_interpolate_instance_q31 S = {L, phaseLength, pCoeffs, pState}; arm_fir_interpolate_instance_q15 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 arm_fir_interpolate_f32  (  const arm_fir_interpolate_instance_f32 *  S, 
float32_t *  pSrc,  
float32_t *  pDst,  
uint32_t  blockSize  
) 
[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. 
References blockSize, arm_fir_interpolate_instance_f32::L, arm_fir_interpolate_instance_f32::pCoeffs, arm_fir_interpolate_instance_f32::phaseLength, and arm_fir_interpolate_instance_f32::pState.
arm_status arm_fir_interpolate_init_f32  (  arm_fir_interpolate_instance_f32 *  S, 
uint8_t  L,  
uint16_t  numTaps,  
float32_t *  pCoeffs,  
float32_t *  pState,  
uint32_t  blockSize  
) 
[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()
. References ARM_MATH_LENGTH_ERROR, ARM_MATH_SUCCESS, arm_fir_interpolate_instance_f32::L, arm_fir_interpolate_instance_f32::pCoeffs, arm_fir_interpolate_instance_f32::phaseLength, arm_fir_interpolate_instance_f32::pState, and status.
arm_status arm_fir_interpolate_init_q15  (  arm_fir_interpolate_instance_q15 *  S, 
uint8_t  L,  
uint16_t  numTaps,  
q15_t *  pCoeffs,  
q15_t *  pState,  
uint32_t  blockSize  
) 
[in,out]  *S  points to an instance of the Q15 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_q15()
. References ARM_MATH_LENGTH_ERROR, ARM_MATH_SUCCESS, arm_fir_interpolate_instance_q15::L, arm_fir_interpolate_instance_q15::pCoeffs, arm_fir_interpolate_instance_q15::phaseLength, arm_fir_interpolate_instance_q15::pState, and status.
arm_status arm_fir_interpolate_init_q31  (  arm_fir_interpolate_instance_q31 *  S, 
uint8_t  L,  
uint16_t  numTaps,  
q31_t *  pCoeffs,  
q31_t *  pState,  
uint32_t  blockSize  
) 
[in,out]  *S  points to an instance of the Q31 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_q31()
. References ARM_MATH_LENGTH_ERROR, ARM_MATH_SUCCESS, arm_fir_interpolate_instance_q31::L, arm_fir_interpolate_instance_q31::pCoeffs, arm_fir_interpolate_instance_q31::phaseLength, arm_fir_interpolate_instance_q31::pState, and status.
void arm_fir_interpolate_q15  (  const arm_fir_interpolate_instance_q15 *  S, 
q15_t *  pSrc,  
q15_t *  pDst,  
uint32_t  blockSize  
) 
[in]  *S  points to an instance of the Q15 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. 
Scaling and Overflow Behavior:
References blockSize, arm_fir_interpolate_instance_q15::L, arm_fir_interpolate_instance_q15::pCoeffs, arm_fir_interpolate_instance_q15::phaseLength, and arm_fir_interpolate_instance_q15::pState.
void arm_fir_interpolate_q31  (  const arm_fir_interpolate_instance_q31 *  S, 
q31_t *  pSrc,  
q31_t *  pDst,  
uint32_t  blockSize  
) 
[in]  *S  points to an instance of the Q31 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. 
Scaling and Overflow Behavior:
1/(numTaps/L)
. since numTaps/L
additions occur per output sample. After all multiplyaccumulates are performed, the 2.62 accumulator is truncated to 1.32 format and then saturated to 1.31 format. References blockSize, arm_fir_interpolate_instance_q31::L, arm_fir_interpolate_instance_q31::pCoeffs, arm_fir_interpolate_instance_q31::phaseLength, and arm_fir_interpolate_instance_q31::pState.