CMSIS DSP Library from CMSIS 2.0. See http://www.onarm.com/cmsis/ for full details
Dependents: K22F_DSP_Matrix_least_square BNO055-ELEC3810 1BNO055 ECE4180Project--Slave2 ... more
Diff: src/Cortex-M4-M3/FilteringFunctions/arm_fir_decimate_fast_q15.c
- Revision:
- 0:1014af42efd9
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/src/Cortex-M4-M3/FilteringFunctions/arm_fir_decimate_fast_q15.c Thu Mar 10 15:07:50 2011 +0000 @@ -0,0 +1,196 @@ +/* ---------------------------------------------------------------------- +* Copyright (C) 2010 ARM Limited. All rights reserved. +* +* $Date: 29. November 2010 +* $Revision: V1.0.3 +* +* Project: CMSIS DSP Library +* Title: arm_fir_decimate_fast_q15.c +* +* Description: Fast Q15 FIR Decimator. +* +* Target Processor: Cortex-M4/Cortex-M3 +* +* Version 1.0.3 2010/11/29 +* Re-organized the CMSIS folders and updated documentation. +* +* Version 1.0.2 2010/11/11 +* Documentation updated. +* +* Version 1.0.1 2010/10/05 +* Production release and review comments incorporated. +* +* Version 1.0.0 2010/09/20 +* Production release and review comments incorporated. +* -------------------------------------------------------------------- */ + +#include "arm_math.h" + +/** + * @ingroup groupFilters + */ + +/** + * @addtogroup FIR_decimate + * @{ + */ + +/** + * @brief Processing function for the Q15 FIR decimator (fast variant). + * @param[in] *S points to an instance of the Q15 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 + * + * <b>Scaling and Overflow Behavior:</b> + * \par + * This fast version uses a 32-bit accumulator with 2.30 format. + * The accumulator maintains full precision of the intermediate multiplication results but provides only a single guard bit. + * Thus, if the accumulator result overflows it wraps around and distorts the result. + * In order to avoid overflows completely the input signal must be scaled down by log2(numTaps) bits (log2 is read as log to the base 2). + * The 2.30 accumulator is then truncated to 2.15 format and saturated to yield the 1.15 result. + * + * \par + * Refer to the function <code>arm_fir_decimate_q15()</code> for a slower implementation of this function which uses 64-bit accumulation to avoid wrap around distortion. + * Both the slow and the fast versions use the same instance structure. + * Use the function <code>arm_fir_decimate_init_q15()</code> to initialize the filter structure. + */ + +void arm_fir_decimate_fast_q15( + const arm_fir_decimate_instance_q15 * S, + q15_t * pSrc, + q15_t * pDst, + uint32_t blockSize) +{ + q15_t *pState = S->pState; /* State pointer */ + q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ + q15_t *pStateCurnt; /* Points to the current sample of the state */ + q15_t *px; /* Temporary pointer for state buffer */ + q15_t *pb; /* Temporary pointer coefficient buffer */ + q31_t x0, c0; /* Temporary variables to hold state and coefficient values */ + q31_t sum0; /* Accumulators */ + uint32_t numTaps = S->numTaps; /* Number of taps */ + uint32_t i, blkCnt, tapCnt, outBlockSize = blockSize / S->M; /* Loop counters */ + + + /* 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 sum to zero */ + sum0 = 0; + + /* 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 Read b[numTaps-1] and b[numTaps-2] coefficients */ + c0 = *__SIMD32(pb)++; + + /* Read x[n-numTaps-1] and x[n-numTaps-2]sample */ + x0 = *__SIMD32(px)++; + + /* Perform the multiply-accumulate */ + sum0 = __SMLAD(x0, c0, sum0); + + /* Read the b[numTaps-3] and b[numTaps-4] coefficient */ + c0 = *__SIMD32(pb)++; + + /* Read x[n-numTaps-2] and x[n-numTaps-3] sample */ + x0 = *__SIMD32(px)++; + + /* Perform the multiply-accumulate */ + sum0 = __SMLAD(x0, c0, sum0); + + /* 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 = __SMLAD(x0, c0, sum0); + + /* 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; + + /* Store filter output , smlad returns the values in 2.14 format */ + /* so downsacle by 15 to get output in 1.15 */ + *pDst++ = (q15_t) ((sum0 >> 15)); + + /* Decrement the loop counter */ + blkCnt--; + } + + /* 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) >> 2u; + + /* copy data */ + while(i > 0u) + { + *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; + *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; + + /* Decrement the loop counter */ + i--; + } + + i = (numTaps - 1u) % 0x04u; + + /* copy data */ + while(i > 0u) + { + *pStateCurnt++ = *pState++; + + /* Decrement the loop counter */ + i--; + } +} + +/** + * @} end of FIR_decimate group + */