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# arm_biquad_cascade_df1_q15.c

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    00001 /* ----------------------------------------------------------------------
    00002 * Copyright (C) 2010 ARM Limited. All rights reserved.
    00003 *
    00004 * $Date:        29. November 2010
    00005 * $Revision:    V1.0.3
    00006 *
    00007 * Project:      CMSIS DSP Library
    00008 * Title:        arm_biquad_cascade_df1_q15.c
    00009 *
    00010 * Description:  Processing function for the
    00011 *               Q15 Biquad cascade DirectFormI(DF1) filter.
    00012 *
    00013 * Target Processor: Cortex-M4/Cortex-M3
    00014 *
    00015 * Version 1.0.3 2010/11/29
    00016 *    Re-organized the CMSIS folders and updated documentation.
    00017 *
    00018 * Version 1.0.2 2010/11/11
    00019 *    Documentation updated.
    00020 *
    00021 * Version 1.0.1 2010/10/05
    00022 *    Production release and review comments incorporated.
    00023 *
    00024 * Version 1.0.0 2010/09/20
    00025 *    Production release and review comments incorporated.
    00026 *
    00027 * Version 0.0.5  2010/04/26
    00028 *    incorporated review comments and updated with latest CMSIS layer
    00029 *
    00030 * Version 0.0.3  2010/03/10
    00031 *    Initial version
    00032 * -------------------------------------------------------------------- */
    00033
    00034 #include "arm_math.h"
    00035
    00067 void arm_biquad_cascade_df1_q15(
    00068   const arm_biquad_casd_df1_inst_q15 * S,
    00069   q15_t * pSrc,
    00070   q15_t * pDst,
    00071   uint32_t blockSize)
    00072 {
    00073   q15_t *pIn = pSrc;                             /*  Source pointer                               */
    00074   q15_t *pOut = pDst;                            /*  Destination pointer                          */
    00075   q31_t in;                                      /*  Temporary variable to hold input value       */
    00076   q31_t out;                                     /*  Temporary variable to hold output value      */
    00077   q15_t b0;                                      /*  Temporary variable to hold bo value          */
    00078   q31_t b1, a1;                                  /*  Filter coefficients                          */
    00079   q31_t state_in, state_out;                     /*  Filter state variables                       */
    00080   q63_t acc;                                     /*  Accumulator                                  */
    00081   int32_t shift = (15 - (int32_t) S->postShift); /*  Post shift                                   */
    00082   q15_t *pState = S->pState;                     /*  State pointer                                */
    00083   q15_t *pCoeffs = S->pCoeffs;                   /*  Coefficient pointer                          */
    00084   q31_t *pState_q31;                             /*  32-bit state pointer for SIMD implementation */
    00085   uint32_t sample, stage = (uint32_t) S->numStages;     /*  Stage loop counter                           */
    00086
    00087
    00088
    00089   do
    00090   {
    00091     /* Initialize state pointer of type q31 */
    00092     pState_q31 = (q31_t *) (pState);
    00093
    00094     /* Read the b0 and 0 coefficients using SIMD  */
    00095     b0 = *__SIMD32(pCoeffs)++;
    00096
    00097     /* Read the b1 and b2 coefficients using SIMD */
    00098     b1 = *__SIMD32(pCoeffs)++;
    00099
    00100     /* Read the a1 and a2 coefficients using SIMD */
    00101     a1 = *__SIMD32(pCoeffs)++;
    00102
    00103     /* Read the input state values from the state buffer:  x[n-1], x[n-2] */
    00104     state_in = (q31_t) (*pState_q31++);
    00105
    00106     /* Read the output state values from the state buffer:  y[n-1], y[n-2] */
    00107     state_out = (q31_t) (*pState_q31);
    00108
    00109     /* Apply loop unrolling and compute 2 output values simultaneously. */
    00110     /*      The variable acc hold output values that are being computed:
    00111      *
    00112      *    acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
    00113      *    acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]
    00114      */
    00115     sample = blockSize >> 1u;
    00116
    00117     /* First part of the processing with loop unrolling.  Compute 2 outputs at a time.
    00118      ** a second loop below computes the remaining 1 sample. */
    00119     while(sample > 0u)
    00120     {
    00121
    00122       /* Read the input */
    00123       in = *__SIMD32(pIn)++;
    00124
    00125       /* out =  b0 * x[n] + 0 * 0 */
    00126       out = (q31_t) b0 * ((q15_t) in);
    00127       /* acc +=  b1 * x[n-1] +  b2 * x[n-2] + out */
    00128       acc = __SMLALD(b1, state_in, out);
    00129       /* acc +=  a1 * y[n-1] +  a2 * y[n-2] */
    00130       acc = __SMLALD(a1, state_out, acc);
    00131
    00132       /* The result is converted from 3.29 to 1.31 if postShift = 1, and then saturation is applied */
    00133       out = __SSAT((acc >> shift), 16);
    00134
    00135       /* Every time after the output is computed state should be updated. */
    00136       /* The states should be updated as:  */
    00137       /* Xn2 = Xn1    */
    00138       /* Xn1 = Xn     */
    00139       /* Yn2 = Yn1    */
    00140       /* Yn1 = acc   */
    00141       /* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
    00142       /* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
    00143       state_in = __PKHBT(in, state_in, 16);
    00144       state_out = __PKHBT(out, state_out, 16);
    00145
    00146       /* out =  b0 * x[n] + 0 * 0 */
    00147       out = (q31_t) b0 * ((q15_t) (in >> 16));
    00148       /* acc +=  b1 * x[n-1] +  b2 * x[n-2] + out */
    00149       acc = __SMLALD(b1, state_in, out);
    00150       /* acc +=  a1 * y[n-1] + a2 * y[n-2] */
    00151       acc = __SMLALD(a1, state_out, acc);
    00152
    00153       /* The result is converted from 3.29 to 1.31 if postShift = 1, and then saturation is applied */
    00154       out = __SSAT((acc >> shift), 16);
    00155
    00156       /* Store the output in the destination buffer. */
    00157       *__SIMD32(pOut)++ = __PKHBT(state_out, out, 16);
    00158
    00159       /* Every time after the output is computed state should be updated. */
    00160       /* The states should be updated as:  */
    00161       /* Xn2 = Xn1    */
    00162       /* Xn1 = Xn     */
    00163       /* Yn2 = Yn1    */
    00164       /* Yn1 = acc   */
    00165       /* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
    00166       /* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
    00167       state_in = __PKHBT(in >> 16, state_in, 16);
    00168       state_out = __PKHBT(out, state_out, 16);
    00169
    00170       /* Decrement the loop counter */
    00171       sample--;
    00172
    00173     }
    00174
    00175     /* If the blockSize is not a multiple of 2, compute any remaining output samples here.
    00176      ** No loop unrolling is used. */
    00177
    00178     if((blockSize & 0x1u) != 0u)
    00179     {
    00180       /* Read the input */
    00181       in = *pIn++;
    00182
    00183       /* out =  b0 * x[n] + 0 * 0 */
    00184       out = (q31_t) in *b0;
    00185       /* acc =  b1 * x[n-1] + b2 * x[n-2] + out */
    00186       acc = __SMLALD(b1, state_in, out);
    00187       /* acc +=  a1 * y[n-1] + a2 * y[n-2] */
    00188       acc = __SMLALD(a1, state_out, acc);
    00189
    00190       /* The result is converted from 3.29 to 1.31 if postShift = 1, and then saturation is applied */
    00191       out = __SSAT((acc >> shift), 16);
    00192
    00193       /* Store the output in the destination buffer. */
    00194       *pOut++ = (q15_t) out;
    00195
    00196       /* Every time after the output is computed state should be updated. */
    00197       /* The states should be updated as:  */
    00198       /* Xn2 = Xn1    */
    00199       /* Xn1 = Xn     */
    00200       /* Yn2 = Yn1    */
    00201       /* Yn1 = acc   */
    00202       /* x[n-N], x[n-N-1] are packed together to make state_in of type q31 */
    00203       /* y[n-N], y[n-N-1] are packed together to make state_out of type q31 */
    00204       state_in = __PKHBT(in, state_in, 16);
    00205       state_out = __PKHBT(out, state_out, 16);
    00206
    00207     }
    00208
    00209     /*  The first stage goes from the input wire to the output wire.  */
    00210     /*  Subsequent numStages occur in-place in the output wire  */
    00211     pIn = pDst;
    00212
    00213     /* Reset the output pointer */
    00214     pOut = pDst;
    00215
    00216     /*  Store the updated state variables back into the state array */
    00217     *__SIMD32(pState)++ = __PKHBT(state_in, (state_in >> 16), 16);
    00218     *__SIMD32(pState)++ = __PKHBT(state_out, (state_out >> 16), 16);
    00219
    00220     /* Decrement the loop counter */
    00221     stage--;
    00222
    00223   } while(stage > 0u);
    00224 }
    00225
    00226

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