/* ---------------------------------------------------------------------- * Copyright (C) 2010-2013 ARM Limited. All rights reserved. * * $Date: 17. January 2013 * $Revision: V1.4.1 * * Project: CMSIS DSP Library * Title: arm_fir_decimate_f32.c * * Description: FIR decimation for floating-point sequences. * * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * - Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * - Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * - Neither the name of ARM LIMITED nor the names of its contributors * may be used to endorse or promote products derived from this * software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * -------------------------------------------------------------------- */ #include "arm_math.h" /** * @ingroup groupFilters */ /** * @defgroup FIR_decimate Finite Impulse Response (FIR) Decimator * * These functions combine an FIR filter together with a decimator. * They are used in multirate systems for reducing the sample rate of a signal without introducing aliasing distortion. * Conceptually, the functions are equivalent to the block diagram below: * \image html FIRDecimator.gif "Components included in the FIR Decimator functions" * When decimating by a factor of M, the signal should be prefiltered by a lowpass filter with a normalized * cutoff frequency of 1/M in order to prevent aliasing distortion. * The user of the function is responsible for providing the filter coefficients. * * The FIR decimator functions provided in the CMSIS DSP Library combine the FIR filter and the decimator in an efficient manner. * Instead of calculating all of the FIR filter outputs and discarding M-1 out of every M, only the * samples output by the decimator are computed. * 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/M output values. * In order to have an integer number of output samples blockSize * must always be a multiple of the decimation factor M. * * The library provides separate functions for Q15, Q31 and floating-point data types. * * \par Algorithm: * The FIR portion of the algorithm uses the standard form filter: * 
    
 *    y[n] = b[0] * x[n] + b[1] * x[n-1] + b[2] * x[n-2] + ...+ b[numTaps-1] * x[n-numTaps+1]    
 *
* where, b[n] are the filter coefficients. * \par * The pCoeffs points to a coefficient array of size numTaps. * Coefficients are stored in time reversed order. * \par * 
    
 *    {b[numTaps-1], b[numTaps-2], b[N-2], ..., b[1], b[0]}    
 *
* \par * pState points to a state array of size numTaps + blockSize - 1. * Samples in the state buffer are stored in the order: * \par * 
    
 *    {x[n-numTaps+1], x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2]....x[0], x[1], ..., x[blockSize-1]}    
 *
* The state variables are updated after each block of data is processed, the coefficients are untouched. * * \par Instance Structure * The coefficients and state variables for a filter are stored together in an instance data structure. * A separate instance structure must be defined for each filter. * Coefficient arrays may be shared among several instances while state variable array should be allocated separately. * There are separate instance structure declarations for each of the 3 supported data types. * * \par Initialization Functions * There is also an associated initialization function for each data type. * The initialization function performs the following operations: * - Sets the values of the internal structure fields. * - Zeros out the values in the state buffer. * - Checks to make sure that the size of the input is a multiple of the decimation factor. * To do this manually without calling the init function, assign the follow subfields of the instance structure: * numTaps, pCoeffs, M (decimation factor), pState. Also set all of the values in pState to zero. * * \par * Use of the initialization function is optional. * However, if the initialization function is used, then the instance structure cannot be placed into a const data section. * To place an instance structure into a const data section, the instance structure must be manually initialized. * The code below statically initializes each of the 3 different data type filter instance structures * 
    
 *arm_fir_decimate_instance_f32 S = {M, numTaps, pCoeffs, pState};    
 *arm_fir_decimate_instance_q31 S = {M, numTaps, pCoeffs, pState};    
 *arm_fir_decimate_instance_q15 S = {M, numTaps, pCoeffs, pState};    
 *
* where M is the decimation factor; numTaps is the number of filter coefficients in the filter; * 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. * * \par Fixed-Point Behavior * Care must be taken when using the fixed-point versions of the FIR decimate filter functions. * In particular, the overflow and saturation behavior of the accumulator used in each function must be considered. * Refer to the function specific documentation below for usage guidelines. */ /** * @addtogroup FIR_decimate * @{ */ /** * @brief Processing function for the floating-point FIR decimator. * @param[in] *S points to an instance of the floating-point FIR decimator structure. * @param[in] *pSrc points to the block of input data. * @param[out] *pDst points to the block of output data. * @param[in] blockSize number of input samples to process per call. * @return none. */ void arm_fir_decimate_f32( const arm_fir_decimate_instance_f32 * S, float32_t * pSrc, float32_t * pDst, uint32_t blockSize) { float32_t *pState = S->pState; /* State pointer */ float32_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ float32_t *pStateCurnt; /* Points to the current sample of the state */ float32_t *px, *pb; /* Temporary pointers for state and coefficient buffers */ float32_t sum0; /* Accumulator */ float32_t x0, c0; /* Temporary variables to hold state and coefficient values */ uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */ uint32_t i, tapCnt, blkCnt, outBlockSize = blockSize / S->M; /* Loop counters */ #ifndef ARM_MATH_CM0_FAMILY uint32_t blkCntN4; float32_t *px0, *px1, *px2, *px3; float32_t acc0, acc1, acc2, acc3; float32_t x1, x2, x3; /* Run the below code for Cortex-M4 and Cortex-M3 */ /* S->pState buffer contains previous frame (numTaps - 1) samples */ /* pStateCurnt points to the location where the new input data should be written */ pStateCurnt = S->pState + (numTaps - 1u); /* Total number of output samples to be computed */ blkCnt = outBlockSize / 4; blkCntN4 = outBlockSize - (4 * blkCnt); while(blkCnt > 0u) { /* Copy 4 * decimation factor number of new input samples into the state buffer */ i = 4 * S->M; do { *pStateCurnt++ = *pSrc++; } while(--i); /* Set accumulators to zero */ acc0 = 0.0f; acc1 = 0.0f; acc2 = 0.0f; acc3 = 0.0f; /* Initialize state pointer for all the samples */ px0 = pState; px1 = pState + S->M; px2 = pState + 2 * S->M; px3 = pState + 3 * S->M; /* Initialize coeff pointer */ pb = pCoeffs; /* Loop unrolling. Process 4 taps at a time. */ tapCnt = numTaps >> 2; /* Loop over the number of taps. Unroll by a factor of 4. ** Repeat until we've computed numTaps-4 coefficients. */ while(tapCnt > 0u) { /* Read the b[numTaps-1] coefficient */ c0 = *(pb++); /* Read x[n-numTaps-1] sample for acc0 */ x0 = *(px0++); /* Read x[n-numTaps-1] sample for acc1 */ x1 = *(px1++); /* Read x[n-numTaps-1] sample for acc2 */ x2 = *(px2++); /* Read x[n-numTaps-1] sample for acc3 */ x3 = *(px3++); /* Perform the multiply-accumulate */ acc0 += x0 * c0; acc1 += x1 * c0; acc2 += x2 * c0; acc3 += x3 * c0; /* Read the b[numTaps-2] coefficient */ c0 = *(pb++); /* Read x[n-numTaps-2] sample for acc0, acc1, acc2, acc3 */ x0 = *(px0++); x1 = *(px1++); x2 = *(px2++); x3 = *(px3++); /* Perform the multiply-accumulate */ acc0 += x0 * c0; acc1 += x1 * c0; acc2 += x2 * c0; acc3 += x3 * c0; /* Read the b[numTaps-3] coefficient */ c0 = *(pb++); /* Read x[n-numTaps-3] sample acc0, acc1, acc2, acc3 */ x0 = *(px0++); x1 = *(px1++); x2 = *(px2++); x3 = *(px3++); /* Perform the multiply-accumulate */ acc0 += x0 * c0; acc1 += x1 * c0; acc2 += x2 * c0; acc3 += x3 * c0; /* Read the b[numTaps-4] coefficient */ c0 = *(pb++); /* Read x[n-numTaps-4] sample acc0, acc1, acc2, acc3 */ x0 = *(px0++); x1 = *(px1++); x2 = *(px2++); x3 = *(px3++); /* Perform the multiply-accumulate */ acc0 += x0 * c0; acc1 += x1 * c0; acc2 += x2 * c0; acc3 += x3 * c0; /* Decrement the loop counter */ tapCnt--; } /* If the filter length is not a multiple of 4, compute the remaining filter taps */ tapCnt = numTaps % 0x4u; while(tapCnt > 0u) { /* Read coefficients */ c0 = *(pb++); /* Fetch state variables for acc0, acc1, acc2, acc3 */ x0 = *(px0++); x1 = *(px1++); x2 = *(px2++); x3 = *(px3++); /* Perform the multiply-accumulate */ acc0 += x0 * c0; acc1 += x1 * c0; acc2 += x2 * c0; acc3 += x3 * c0; /* Decrement the loop counter */ tapCnt--; } /* Advance the state pointer by the decimation factor * to process the next group of decimation factor number samples */ pState = pState + 4 * S->M; /* The result is in the accumulator, store in the destination buffer. */ *pDst++ = acc0; *pDst++ = acc1; *pDst++ = acc2; *pDst++ = acc3; /* Decrement the loop counter */ blkCnt--; } while(blkCntN4 > 0u) { /* Copy decimation factor number of new input samples into the state buffer */ i = S->M; do { *pStateCurnt++ = *pSrc++; } while(--i); /* Set accumulator to zero */ sum0 = 0.0f; /* Initialize state pointer */ px = pState; /* Initialize coeff pointer */ pb = pCoeffs; /* Loop unrolling. Process 4 taps at a time. */ tapCnt = numTaps >> 2; /* Loop over the number of taps. Unroll by a factor of 4. ** Repeat until we've computed numTaps-4 coefficients. */ while(tapCnt > 0u) { /* Read the b[numTaps-1] coefficient */ c0 = *(pb++); /* Read x[n-numTaps-1] sample */ x0 = *(px++); /* Perform the multiply-accumulate */ sum0 += x0 * c0; /* Read the b[numTaps-2] coefficient */ c0 = *(pb++); /* Read x[n-numTaps-2] sample */ x0 = *(px++); /* Perform the multiply-accumulate */ sum0 += x0 * c0; /* Read the b[numTaps-3] coefficient */ c0 = *(pb++); /* Read x[n-numTaps-3] sample */ x0 = *(px++); /* Perform the multiply-accumulate */ sum0 += x0 * c0; /* Read the b[numTaps-4] coefficient */ c0 = *(pb++); /* Read x[n-numTaps-4] sample */ x0 = *(px++); /* Perform the multiply-accumulate */ sum0 += x0 * c0; /* Decrement the loop counter */ tapCnt--; } /* If the filter length is not a multiple of 4, compute the remaining filter taps */ tapCnt = numTaps % 0x4u; while(tapCnt > 0u) { /* Read coefficients */ c0 = *(pb++); /* Fetch 1 state variable */ x0 = *(px++); /* Perform the multiply-accumulate */ sum0 += x0 * c0; /* Decrement the loop counter */ tapCnt--; } /* Advance the state pointer by the decimation factor * to process the next group of decimation factor number samples */ pState = pState + S->M; /* The result is in the accumulator, store in the destination buffer. */ *pDst++ = sum0; /* Decrement the loop counter */ blkCntN4--; } /* Processing is complete. ** Now copy the last numTaps - 1 samples to the satrt of the state buffer. ** This prepares the state buffer for the next function call. */ /* Points to the start of the state buffer */ pStateCurnt = S->pState; i = (numTaps - 1u) >> 2; /* copy data */ while(i > 0u) { *pStateCurnt++ = *pState++; *pStateCurnt++ = *pState++; *pStateCurnt++ = *pState++; *pStateCurnt++ = *pState++; /* Decrement the loop counter */ i--; } i = (numTaps - 1u) % 0x04u; /* copy data */ while(i > 0u) { *pStateCurnt++ = *pState++; /* Decrement the loop counter */ i--; } #else /* Run the below code for Cortex-M0 */ /* S->pState buffer contains previous frame (numTaps - 1) samples */ /* pStateCurnt points to the location where the new input data should be written */ pStateCurnt = S->pState + (numTaps - 1u); /* Total number of output samples to be computed */ blkCnt = outBlockSize; while(blkCnt > 0u) { /* Copy decimation factor number of new input samples into the state buffer */ i = S->M; do { *pStateCurnt++ = *pSrc++; } while(--i); /* Set accumulator to zero */ sum0 = 0.0f; /* Initialize state pointer */ px = pState; /* Initialize coeff pointer */ pb = pCoeffs; tapCnt = numTaps; while(tapCnt > 0u) { /* Read coefficients */ c0 = *pb++; /* Fetch 1 state variable */ x0 = *px++; /* Perform the multiply-accumulate */ sum0 += x0 * c0; /* Decrement the loop counter */ tapCnt--; } /* Advance the state pointer by the decimation factor * to process the next group of decimation factor number samples */ pState = pState + S->M; /* The result is in the accumulator, store in the destination buffer. */ *pDst++ = sum0; /* Decrement the loop counter */ blkCnt--; } /* Processing is complete. ** Now copy the last numTaps - 1 samples to the start of the state buffer. ** This prepares the state buffer for the next function call. */ /* Points to the start of the state buffer */ pStateCurnt = S->pState; /* Copy numTaps number of values */ i = (numTaps - 1u); /* copy data */ while(i > 0u) { *pStateCurnt++ = *pState++; /* Decrement the loop counter */ i--; } #endif /* #ifndef ARM_MATH_CM0_FAMILY */ } /** * @} end of FIR_decimate group */