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src/Cortex-M4-M3/FilteringFunctions/arm_biquad_cascade_df1_q15.c@0:1014af42efd9, 2011-03-10 (annotated)

Committer:: simon
Date:: Thu Mar 10 15:07:50 2011 +0000
Revision:: 0:1014af42efd9

Who changed what in which revision?

User	Revision	Line number	New contents of line
simon	0:1014af42efd9	1	/* ----------------------------------------------------------------------
simon	0:1014af42efd9	2	* Copyright (C) 2010 ARM Limited. All rights reserved.
simon	0:1014af42efd9	3	*
simon	0:1014af42efd9	4	* $Date: 29. November 2010
simon	0:1014af42efd9	5	* $Revision: V1.0.3
simon	0:1014af42efd9	6	*
simon	0:1014af42efd9	7	* Project: CMSIS DSP Library
simon	0:1014af42efd9	8	* Title: arm_biquad_cascade_df1_q15.c
simon	0:1014af42efd9	9	*
simon	0:1014af42efd9	10	* Description: Processing function for the
simon	0:1014af42efd9	11	* Q15 Biquad cascade DirectFormI(DF1) filter.
simon	0:1014af42efd9	12	*
simon	0:1014af42efd9	13	* Target Processor: Cortex-M4/Cortex-M3
simon	0:1014af42efd9	14	*
simon	0:1014af42efd9	15	* Version 1.0.3 2010/11/29
simon	0:1014af42efd9	16	* Re-organized the CMSIS folders and updated documentation.
simon	0:1014af42efd9	17	*
simon	0:1014af42efd9	18	* Version 1.0.2 2010/11/11
simon	0:1014af42efd9	19	* Documentation updated.
simon	0:1014af42efd9	20	*
simon	0:1014af42efd9	21	* Version 1.0.1 2010/10/05
simon	0:1014af42efd9	22	* Production release and review comments incorporated.
simon	0:1014af42efd9	23	*
simon	0:1014af42efd9	24	* Version 1.0.0 2010/09/20
simon	0:1014af42efd9	25	* Production release and review comments incorporated.
simon	0:1014af42efd9	26	*
simon	0:1014af42efd9	27	* Version 0.0.5 2010/04/26
simon	0:1014af42efd9	28	* incorporated review comments and updated with latest CMSIS layer
simon	0:1014af42efd9	29	*
simon	0:1014af42efd9	30	* Version 0.0.3 2010/03/10
simon	0:1014af42efd9	31	* Initial version
simon	0:1014af42efd9	32	* -------------------------------------------------------------------- */
simon	0:1014af42efd9	33
simon	0:1014af42efd9	34	#include "arm_math.h"
simon	0:1014af42efd9	35
simon	0:1014af42efd9	36	/**
simon	0:1014af42efd9	37	* @ingroup groupFilters
simon	0:1014af42efd9	38	*/
simon	0:1014af42efd9	39
simon	0:1014af42efd9	40	/**
simon	0:1014af42efd9	41	* @addtogroup BiquadCascadeDF1
simon	0:1014af42efd9	42	* @{
simon	0:1014af42efd9	43	*/
simon	0:1014af42efd9	44
simon	0:1014af42efd9	45	/**
simon	0:1014af42efd9	46	* @brief Processing function for the Q15 Biquad cascade filter.
simon	0:1014af42efd9	47	* @param[in] *S points to an instance of the Q15 Biquad cascade structure.
simon	0:1014af42efd9	48	* @param[in] *pSrc points to the block of input data.
simon	0:1014af42efd9	49	* @param[out] *pDst points to the location where the output result is written.
simon	0:1014af42efd9	50	* @param[in] blockSize number of samples to process per call.
simon	0:1014af42efd9	51	* @return none.
simon	0:1014af42efd9	52	*
simon	0:1014af42efd9	53	*
simon	0:1014af42efd9	54	* <b>Scaling and Overflow Behavior:</b>
simon	0:1014af42efd9	55	* \par
simon	0:1014af42efd9	56	* The function is implemented using a 64-bit internal accumulator.
simon	0:1014af42efd9	57	* Both coefficients and state variables are represented in 1.15 format and multiplications yield a 2.30 result.
simon	0:1014af42efd9	58	* The 2.30 intermediate results are accumulated in a 64-bit accumulator in 34.30 format.
simon	0:1014af42efd9	59	* There is no risk of internal overflow with this approach and the full precision of intermediate multiplications is preserved.
simon	0:1014af42efd9	60	* The accumulator is then shifted by <code>postShift</code> bits to truncate the result to 1.15 format by discarding the low 16 bits.
simon	0:1014af42efd9	61	* Finally, the result is saturated to 1.15 format.
simon	0:1014af42efd9	62	*
simon	0:1014af42efd9	63	* \par
simon	0:1014af42efd9	64	* Refer to the function <code>arm_biquad_cascade_df1_fast_q15()</code> for a faster but less precise implementation of this filter.
simon	0:1014af42efd9	65	*/
simon	0:1014af42efd9	66
simon	0:1014af42efd9	67	void arm_biquad_cascade_df1_q15(
simon	0:1014af42efd9	68	const arm_biquad_casd_df1_inst_q15 * S,
simon	0:1014af42efd9	69	q15_t * pSrc,
simon	0:1014af42efd9	70	q15_t * pDst,
simon	0:1014af42efd9	71	uint32_t blockSize)
simon	0:1014af42efd9	72	{
simon	0:1014af42efd9	73	q15_t pIn = pSrc; / Source pointer */
simon	0:1014af42efd9	74	q15_t pOut = pDst; / Destination pointer */
simon	0:1014af42efd9	75	q31_t in; /* Temporary variable to hold input value */
simon	0:1014af42efd9	76	q31_t out; /* Temporary variable to hold output value */
simon	0:1014af42efd9	77	q15_t b0; /* Temporary variable to hold bo value */
simon	0:1014af42efd9	78	q31_t b1, a1; /* Filter coefficients */
simon	0:1014af42efd9	79	q31_t state_in, state_out; /* Filter state variables */
simon	0:1014af42efd9	80	q63_t acc; /* Accumulator */
simon	0:1014af42efd9	81	int32_t shift = (15 - (int32_t) S->postShift); /* Post shift */
simon	0:1014af42efd9	82	q15_t pState = S->pState; / State pointer */
simon	0:1014af42efd9	83	q15_t pCoeffs = S->pCoeffs; / Coefficient pointer */
simon	0:1014af42efd9	84	q31_t pState_q31; / 32-bit state pointer for SIMD implementation */
simon	0:1014af42efd9	85	uint32_t sample, stage = (uint32_t) S->numStages; /* Stage loop counter */
simon	0:1014af42efd9	86
simon	0:1014af42efd9	87
simon	0:1014af42efd9	88
simon	0:1014af42efd9	89	do
simon	0:1014af42efd9	90	{
simon	0:1014af42efd9	91	/* Initialize state pointer of type q31 */
simon	0:1014af42efd9	92	pState_q31 = (q31_t *) (pState);
simon	0:1014af42efd9	93
simon	0:1014af42efd9	94	/* Read the b0 and 0 coefficients using SIMD */
simon	0:1014af42efd9	95	b0 = *__SIMD32(pCoeffs)++;
simon	0:1014af42efd9	96
simon	0:1014af42efd9	97	/* Read the b1 and b2 coefficients using SIMD */
simon	0:1014af42efd9	98	b1 = *__SIMD32(pCoeffs)++;
simon	0:1014af42efd9	99
simon	0:1014af42efd9	100	/* Read the a1 and a2 coefficients using SIMD */
simon	0:1014af42efd9	101	a1 = *__SIMD32(pCoeffs)++;
simon	0:1014af42efd9	102
simon	0:1014af42efd9	103	/* Read the input state values from the state buffer: x[n-1], x[n-2] */
simon	0:1014af42efd9	104	state_in = (q31_t) (*pState_q31++);
simon	0:1014af42efd9	105
simon	0:1014af42efd9	106	/* Read the output state values from the state buffer: y[n-1], y[n-2] */
simon	0:1014af42efd9	107	state_out = (q31_t) (*pState_q31);
simon	0:1014af42efd9	108
simon	0:1014af42efd9	109	/* Apply loop unrolling and compute 2 output values simultaneously. */
simon	0:1014af42efd9	110	/* The variable acc hold output values that are being computed:
simon	0:1014af42efd9	111	*
simon	0:1014af42efd9	112	* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
simon	0:1014af42efd9	113	* acc = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
simon	0:1014af42efd9	114	*/
simon	0:1014af42efd9	115	sample = blockSize >> 1u;
simon	0:1014af42efd9	116
simon	0:1014af42efd9	117	/* First part of the processing with loop unrolling. Compute 2 outputs at a time.
simon	0:1014af42efd9	118	** a second loop below computes the remaining 1 sample. */
simon	0:1014af42efd9	119	while(sample > 0u)
simon	0:1014af42efd9	120	{
simon	0:1014af42efd9	121
simon	0:1014af42efd9	122	/* Read the input */
simon	0:1014af42efd9	123	in = *__SIMD32(pIn)++;
simon	0:1014af42efd9	124
simon	0:1014af42efd9	125	/* out = b0 * x[n] + 0 * 0 */
simon	0:1014af42efd9	126	out = (q31_t) b0 * ((q15_t) in);
simon	0:1014af42efd9	127	/* acc += b1 * x[n-1] + b2 * x[n-2] + out */
simon	0:1014af42efd9	128	acc = __SMLALD(b1, state_in, out);
simon	0:1014af42efd9	129	/* acc += a1 * y[n-1] + a2 * y[n-2] */
simon	0:1014af42efd9	130	acc = __SMLALD(a1, state_out, acc);
simon	0:1014af42efd9	131
simon	0:1014af42efd9	132	/* The result is converted from 3.29 to 1.31 if postShift = 1, and then saturation is applied */
simon	0:1014af42efd9	133	out = __SSAT((acc >> shift), 16);
simon	0:1014af42efd9	134
simon	0:1014af42efd9	135	/* Every time after the output is computed state should be updated. */
simon	0:1014af42efd9	136	/* The states should be updated as: */
simon	0:1014af42efd9	137	/* Xn2 = Xn1 */
simon	0:1014af42efd9	138	/* Xn1 = Xn */
simon	0:1014af42efd9	139	/* Yn2 = Yn1 */
simon	0:1014af42efd9	140	/* Yn1 = acc */
simon	0:1014af42efd9	141	/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
simon	0:1014af42efd9	142	/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
simon	0:1014af42efd9	143	state_in = __PKHBT(in, state_in, 16);
simon	0:1014af42efd9	144	state_out = __PKHBT(out, state_out, 16);
simon	0:1014af42efd9	145
simon	0:1014af42efd9	146	/* out = b0 * x[n] + 0 * 0 */
simon	0:1014af42efd9	147	out = (q31_t) b0 * ((q15_t) (in >> 16));
simon	0:1014af42efd9	148	/* acc += b1 * x[n-1] + b2 * x[n-2] + out */
simon	0:1014af42efd9	149	acc = __SMLALD(b1, state_in, out);
simon	0:1014af42efd9	150	/* acc += a1 * y[n-1] + a2 * y[n-2] */
simon	0:1014af42efd9	151	acc = __SMLALD(a1, state_out, acc);
simon	0:1014af42efd9	152
simon	0:1014af42efd9	153	/* The result is converted from 3.29 to 1.31 if postShift = 1, and then saturation is applied */
simon	0:1014af42efd9	154	out = __SSAT((acc >> shift), 16);
simon	0:1014af42efd9	155
simon	0:1014af42efd9	156	/* Store the output in the destination buffer. */
simon	0:1014af42efd9	157	*__SIMD32(pOut)++ = __PKHBT(state_out, out, 16);
simon	0:1014af42efd9	158
simon	0:1014af42efd9	159	/* Every time after the output is computed state should be updated. */
simon	0:1014af42efd9	160	/* The states should be updated as: */
simon	0:1014af42efd9	161	/* Xn2 = Xn1 */
simon	0:1014af42efd9	162	/* Xn1 = Xn */
simon	0:1014af42efd9	163	/* Yn2 = Yn1 */
simon	0:1014af42efd9	164	/* Yn1 = acc */
simon	0:1014af42efd9	165	/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
simon	0:1014af42efd9	166	/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
simon	0:1014af42efd9	167	state_in = __PKHBT(in >> 16, state_in, 16);
simon	0:1014af42efd9	168	state_out = __PKHBT(out, state_out, 16);
simon	0:1014af42efd9	169
simon	0:1014af42efd9	170	/* Decrement the loop counter */
simon	0:1014af42efd9	171	sample--;
simon	0:1014af42efd9	172
simon	0:1014af42efd9	173	}
simon	0:1014af42efd9	174
simon	0:1014af42efd9	175	/* If the blockSize is not a multiple of 2, compute any remaining output samples here.
simon	0:1014af42efd9	176	** No loop unrolling is used. */
simon	0:1014af42efd9	177
simon	0:1014af42efd9	178	if((blockSize & 0x1u) != 0u)
simon	0:1014af42efd9	179	{
simon	0:1014af42efd9	180	/* Read the input */
simon	0:1014af42efd9	181	in = *pIn++;
simon	0:1014af42efd9	182
simon	0:1014af42efd9	183	/* out = b0 * x[n] + 0 * 0 */
simon	0:1014af42efd9	184	out = (q31_t) in *b0;
simon	0:1014af42efd9	185	/* acc = b1 * x[n-1] + b2 * x[n-2] + out */
simon	0:1014af42efd9	186	acc = __SMLALD(b1, state_in, out);
simon	0:1014af42efd9	187	/* acc += a1 * y[n-1] + a2 * y[n-2] */
simon	0:1014af42efd9	188	acc = __SMLALD(a1, state_out, acc);
simon	0:1014af42efd9	189
simon	0:1014af42efd9	190	/* The result is converted from 3.29 to 1.31 if postShift = 1, and then saturation is applied */
simon	0:1014af42efd9	191	out = __SSAT((acc >> shift), 16);
simon	0:1014af42efd9	192
simon	0:1014af42efd9	193	/* Store the output in the destination buffer. */
simon	0:1014af42efd9	194	*pOut++ = (q15_t) out;
simon	0:1014af42efd9	195
simon	0:1014af42efd9	196	/* Every time after the output is computed state should be updated. */
simon	0:1014af42efd9	197	/* The states should be updated as: */
simon	0:1014af42efd9	198	/* Xn2 = Xn1 */
simon	0:1014af42efd9	199	/* Xn1 = Xn */
simon	0:1014af42efd9	200	/* Yn2 = Yn1 */
simon	0:1014af42efd9	201	/* Yn1 = acc */
simon	0:1014af42efd9	202	/* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
simon	0:1014af42efd9	203	/* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
simon	0:1014af42efd9	204	state_in = __PKHBT(in, state_in, 16);
simon	0:1014af42efd9	205	state_out = __PKHBT(out, state_out, 16);
simon	0:1014af42efd9	206
simon	0:1014af42efd9	207	}
simon	0:1014af42efd9	208
simon	0:1014af42efd9	209	/* The first stage goes from the input wire to the output wire. */
simon	0:1014af42efd9	210	/* Subsequent numStages occur in-place in the output wire */
simon	0:1014af42efd9	211	pIn = pDst;
simon	0:1014af42efd9	212
simon	0:1014af42efd9	213	/* Reset the output pointer */
simon	0:1014af42efd9	214	pOut = pDst;
simon	0:1014af42efd9	215
simon	0:1014af42efd9	216	/* Store the updated state variables back into the state array */
simon	0:1014af42efd9	217	*__SIMD32(pState)++ = __PKHBT(state_in, (state_in >> 16), 16);
simon	0:1014af42efd9	218	*__SIMD32(pState)++ = __PKHBT(state_out, (state_out >> 16), 16);
simon	0:1014af42efd9	219
simon	0:1014af42efd9	220	/* Decrement the loop counter */
simon	0:1014af42efd9	221	stage--;
simon	0:1014af42efd9	222
simon	0:1014af42efd9	223	} while(stage > 0u);
simon	0:1014af42efd9	224	}
simon	0:1014af42efd9	225
simon	0:1014af42efd9	226
simon	0:1014af42efd9	227	/**
simon	0:1014af42efd9	228	* @} end of BiquadCascadeDF1 group
simon	0:1014af42efd9	229	*/

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Type:	Library
Created:	10 Mar 2011
Imports:	907
Forks:	1
Commits:	3
Dependents:	5
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src/Cortex-M4-M3/FilteringFunctions/arm_biquad_cascade_df1_q15.c@0:1014af42efd9, 2011-03-10 (annotated)

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