/* ---------------------------------------------------------------------- * Project: CMSIS DSP Library * Title: arm_fir_q7.c * Description: Q7 FIR filter processing function * * $Date: 27. January 2017 * $Revision: V.1.5.1 * * Target Processor: Cortex-M cores * -------------------------------------------------------------------- */ /* * Copyright (C) 2010-2017 ARM Limited or its affiliates. All rights reserved. * * SPDX-License-Identifier: Apache-2.0 * * Licensed under the Apache License, Version 2.0 (the License); you may * not use this file except in compliance with the License. * You may obtain a copy of the License at * * www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an AS IS BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ #include "arm_math.h" /** * @ingroup groupFilters */ /** * @addtogroup FIR * @{ */ /** * @param[in] *S points to an instance of the Q7 FIR filter 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 samples to process per call. * @return none. * * Scaling and Overflow Behavior: * \par * The function is implemented using a 32-bit internal accumulator. * Both coefficients and state variables are represented in 1.7 format and multiplications yield a 2.14 result. * The 2.14 intermediate results are accumulated in a 32-bit accumulator in 18.14 format. * There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved. * The accumulator is converted to 18.7 format by discarding the low 7 bits. * Finally, the result is truncated to 1.7 format. */ void arm_fir_q7( const arm_fir_instance_q7 * S, q7_t * pSrc, q7_t * pDst, uint32_t blockSize) { #if defined (ARM_MATH_DSP) /* Run the below code for Cortex-M4 and Cortex-M3 */ q7_t *pState = S->pState; /* State pointer */ q7_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ q7_t *pStateCurnt; /* Points to the current sample of the state */ q7_t x0, x1, x2, x3; /* Temporary variables to hold state */ q7_t c0; /* Temporary variable to hold coefficient value */ q7_t *px; /* Temporary pointer for state */ q7_t *pb; /* Temporary pointer for coefficient buffer */ q31_t acc0, acc1, acc2, acc3; /* Accumulators */ uint32_t numTaps = S->numTaps; /* Number of filter coefficients in the filter */ uint32_t i, tapCnt, blkCnt; /* Loop counters */ /* S->pState points to state array which contains previous frame (numTaps - 1) samples */ /* pStateCurnt points to the location where the new input data should be written */ pStateCurnt = &(S->pState[(numTaps - 1U)]); /* Apply loop unrolling and compute 4 output values simultaneously. * The variables acc0 ... acc3 hold output values that are being computed: * * acc0 = b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0] * acc1 = b[numTaps-1] * x[n-numTaps] + b[numTaps-2] * x[n-numTaps-1] + b[numTaps-3] * x[n-numTaps-2] +...+ b[0] * x[1] * acc2 = b[numTaps-1] * x[n-numTaps+1] + b[numTaps-2] * x[n-numTaps] + b[numTaps-3] * x[n-numTaps-1] +...+ b[0] * x[2] * acc3 = b[numTaps-1] * x[n-numTaps+2] + b[numTaps-2] * x[n-numTaps+1] + b[numTaps-3] * x[n-numTaps] +...+ b[0] * x[3] */ blkCnt = blockSize >> 2; /* First part of the processing with loop unrolling. Compute 4 outputs at a time. ** a second loop below computes the remaining 1 to 3 samples. */ while (blkCnt > 0U) { /* Copy four new input samples into the state buffer */ *pStateCurnt++ = *pSrc++; *pStateCurnt++ = *pSrc++; *pStateCurnt++ = *pSrc++; *pStateCurnt++ = *pSrc++; /* Set all accumulators to zero */ acc0 = 0; acc1 = 0; acc2 = 0; acc3 = 0; /* Initialize state pointer */ px = pState; /* Initialize coefficient pointer */ pb = pCoeffs; /* Read the first three samples from the state buffer: * x[n-numTaps], x[n-numTaps-1], x[n-numTaps-2] */ x0 = *(px++); x1 = *(px++); x2 = *(px++); /* Loop unrolling. Process 4 taps at a time. */ tapCnt = numTaps >> 2; i = tapCnt; while (i > 0U) { /* Read the b[numTaps] coefficient */ c0 = *pb; /* Read x[n-numTaps-3] sample */ x3 = *px; /* acc0 += b[numTaps] * x[n-numTaps] */ acc0 += ((q15_t) x0 * c0); /* acc1 += b[numTaps] * x[n-numTaps-1] */ acc1 += ((q15_t) x1 * c0); /* acc2 += b[numTaps] * x[n-numTaps-2] */ acc2 += ((q15_t) x2 * c0); /* acc3 += b[numTaps] * x[n-numTaps-3] */ acc3 += ((q15_t) x3 * c0); /* Read the b[numTaps-1] coefficient */ c0 = *(pb + 1U); /* Read x[n-numTaps-4] sample */ x0 = *(px + 1U); /* Perform the multiply-accumulates */ acc0 += ((q15_t) x1 * c0); acc1 += ((q15_t) x2 * c0); acc2 += ((q15_t) x3 * c0); acc3 += ((q15_t) x0 * c0); /* Read the b[numTaps-2] coefficient */ c0 = *(pb + 2U); /* Read x[n-numTaps-5] sample */ x1 = *(px + 2U); /* Perform the multiply-accumulates */ acc0 += ((q15_t) x2 * c0); acc1 += ((q15_t) x3 * c0); acc2 += ((q15_t) x0 * c0); acc3 += ((q15_t) x1 * c0); /* Read the b[numTaps-3] coefficients */ c0 = *(pb + 3U); /* Read x[n-numTaps-6] sample */ x2 = *(px + 3U); /* Perform the multiply-accumulates */ acc0 += ((q15_t) x3 * c0); acc1 += ((q15_t) x0 * c0); acc2 += ((q15_t) x1 * c0); acc3 += ((q15_t) x2 * c0); /* update coefficient pointer */ pb += 4U; px += 4U; /* Decrement the loop counter */ i--; } /* If the filter length is not a multiple of 4, compute the remaining filter taps */ i = numTaps - (tapCnt * 4U); while (i > 0U) { /* Read coefficients */ c0 = *(pb++); /* Fetch 1 state variable */ x3 = *(px++); /* Perform the multiply-accumulates */ acc0 += ((q15_t) x0 * c0); acc1 += ((q15_t) x1 * c0); acc2 += ((q15_t) x2 * c0); acc3 += ((q15_t) x3 * c0); /* Reuse the present sample states for next sample */ x0 = x1; x1 = x2; x2 = x3; /* Decrement the loop counter */ i--; } /* Advance the state pointer by 4 to process the next group of 4 samples */ pState = pState + 4; /* The results in the 4 accumulators are in 2.62 format. Convert to 1.31 ** Then store the 4 outputs in the destination buffer. */ acc0 = __SSAT((acc0 >> 7U), 8); *pDst++ = acc0; acc1 = __SSAT((acc1 >> 7U), 8); *pDst++ = acc1; acc2 = __SSAT((acc2 >> 7U), 8); *pDst++ = acc2; acc3 = __SSAT((acc3 >> 7U), 8); *pDst++ = acc3; /* Decrement the samples loop counter */ blkCnt--; } /* If the blockSize is not a multiple of 4, compute any remaining output samples here. ** No loop unrolling is used. */ blkCnt = blockSize % 4U; while (blkCnt > 0U) { /* Copy one sample at a time into state buffer */ *pStateCurnt++ = *pSrc++; /* Set the accumulator to zero */ acc0 = 0; /* Initialize state pointer */ px = pState; /* Initialize Coefficient pointer */ pb = (pCoeffs); i = numTaps; /* Perform the multiply-accumulates */ do { acc0 += (q15_t) * (px++) * (*(pb++)); i--; } while (i > 0U); /* The result is in 2.14 format. Convert to 1.7 ** Then store the output in the destination buffer. */ *pDst++ = __SSAT((acc0 >> 7U), 8); /* Advance state pointer by 1 for the next sample */ pState = pState + 1; /* Decrement the samples 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; tapCnt = (numTaps - 1U) >> 2U; /* copy data */ while (tapCnt > 0U) { *pStateCurnt++ = *pState++; *pStateCurnt++ = *pState++; *pStateCurnt++ = *pState++; *pStateCurnt++ = *pState++; /* Decrement the loop counter */ tapCnt--; } /* Calculate remaining number of copies */ tapCnt = (numTaps - 1U) % 0x4U; /* Copy the remaining q31_t data */ while (tapCnt > 0U) { *pStateCurnt++ = *pState++; /* Decrement the loop counter */ tapCnt--; } #else /* Run the below code for Cortex-M0 */ uint32_t numTaps = S->numTaps; /* Number of taps in the filter */ uint32_t i, blkCnt; /* Loop counters */ q7_t *pState = S->pState; /* State pointer */ q7_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ q7_t *px, *pb; /* Temporary pointers to state and coeff */ q31_t acc = 0; /* Accumlator */ q7_t *pStateCurnt; /* Points to the current sample of the state */ /* S->pState points to state array which contains previous frame (numTaps - 1) samples */ /* pStateCurnt points to the location where the new input data should be written */ pStateCurnt = S->pState + (numTaps - 1U); /* Initialize blkCnt with blockSize */ blkCnt = blockSize; /* Perform filtering upto BlockSize - BlockSize%4 */ while (blkCnt > 0U) { /* Copy one sample at a time into state buffer */ *pStateCurnt++ = *pSrc++; /* Set accumulator to zero */ acc = 0; /* Initialize state pointer of type q7 */ px = pState; /* Initialize coeff pointer of type q7 */ pb = pCoeffs; i = numTaps; while (i > 0U) { /* acc = b[numTaps-1] * x[n-numTaps-1] + b[numTaps-2] * x[n-numTaps-2] + b[numTaps-3] * x[n-numTaps-3] +...+ b[0] * x[0] */ acc += (q15_t) * px++ * *pb++; i--; } /* Store the 1.7 format filter output in destination buffer */ *pDst++ = (q7_t) __SSAT((acc >> 7), 8); /* Advance the state pointer by 1 to process the next sample */ pState = pState + 1; /* 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; /* Copy numTaps number of values */ i = (numTaps - 1U); /* Copy q7_t data */ while (i > 0U) { *pStateCurnt++ = *pState++; i--; } #endif /* #if defined (ARM_MATH_DSP) */ } /** * @} end of FIR group */