Functions | |
| 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) |
| void | arm_fir_interpolate_f32 (const arm_fir_interpolate_instance_f32 *S, float32_t *pSrc, float32_t *pDst, uint32_t blockSize) |
| 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) |
| void | arm_fir_interpolate_q31 (const arm_fir_interpolate_instance_q31 *S, q31_t *pSrc, q31_t *pDst, uint32_t blockSize) |
| 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) |
| void | arm_fir_interpolate_q15 (const arm_fir_interpolate_instance_q15 *S, q15_t *pSrc, q15_t *pDst, uint32_t blockSize) |
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:
Components included in the FIR Interpolator functions
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 L-1 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 floating-point data types.
y[n] = b[0] * x[n] + b[L] * x[n-1] + ... + b[L*(phaseLength-1)] * x[n-phaseLength+1]
y[n+1] = b[1] * x[n] + b[L+1] * x[n-1] + ... + b[L*(phaseLength-1)+1] * x[n-phaseLength+1]
...
y[n+(L-1)] = b[L-1] * x[n] + b[2*L-1] * x[n-1] + ....+ b[L*(phaseLength-1)+(L-1)] * x[n-phaseLength+1]
This approach is more efficient than straightforward upsample-then-filter 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[numTaps-1], b[numTaps-2], b[N-2], ..., 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[n-phaseLength+1], x[n-phaseLength], x[n-phaseLength-1], x[n-phaseLength-2]....x[0], x[1], ..., x[blockSize-1]}
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.| 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 floating-point FIR interpolator.
| [in,out] | *S | points to an instance of the floating-point 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[numTaps-1], b[numTaps-2], b[numTaps-2], ..., 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)+blockSize-1 words where blockSize is the number of input samples processed by each call to arm_fir_interpolate_f32(). Definition at line 68 of file arm_fir_interpolate_init_f32.c.
| 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 floating-point FIR interpolator.
| [in] | *S | points to an instance of the floating-point 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. |
Definition at line 135 of file arm_fir_interpolate_f32.c.
| 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.
| [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[numTaps-1], b[numTaps-2], b[numTaps-2], ..., 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)+blockSize-1 words where blockSize is the number of input samples processed by each call to arm_fir_interpolate_q31(). Definition at line 69 of file arm_fir_interpolate_init_q31.c.
| 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.
| [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 multiply-accumulates are performed, the 2.62 accumulator is truncated to 1.32 format and then saturated to 1.31 format. Definition at line 63 of file arm_fir_interpolate_q31.c.
| 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.
| [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[numTaps-1], b[numTaps-2], b[numTaps-2], ..., 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)+blockSize-1 words where blockSize is the number of input samples processed by each call to arm_fir_interpolate_q15(). Definition at line 68 of file arm_fir_interpolate_init_q15.c.
| 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.
| [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:
Definition at line 62 of file arm_fir_interpolate_q15.c.
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