00001 /* ---------------------------------------------------------------------- 00002 * Copyright (C) 2010 ARM Limited. All rights reserved. 00003 * 00004 * $Date: 15. July 2011 00005 * $Revision: V1.0.10 00006 * 00007 * Project: CMSIS DSP Library 00008 * Title: arm_fir_decimate_q15.c 00009 * 00010 * Description: Q15 FIR Decimator. 00011 * 00012 * Target Processor: Cortex-M4/Cortex-M3/Cortex-M0 00013 * 00014 * Version 1.0.10 2011/7/15 00015 * Big Endian support added and Merged M0 and M3/M4 Source code. 00016 * 00017 * Version 1.0.3 2010/11/29 00018 * Re-organized the CMSIS folders and updated documentation. 00019 * 00020 * Version 1.0.2 2010/11/11 00021 * Documentation updated. 00022 * 00023 * Version 1.0.1 2010/10/05 00024 * Production release and review comments incorporated. 00025 * 00026 * Version 1.0.0 2010/09/20 00027 * Production release and review comments incorporated 00028 * 00029 * Version 0.0.7 2010/06/10 00030 * Misra-C changes done 00031 * -------------------------------------------------------------------- */ 00032 00033 #include "arm_math.h" 00034 00065 void arm_fir_decimate_q15( 00066 const arm_fir_decimate_instance_q15 * S, 00067 q15_t * pSrc, 00068 q15_t * pDst, 00069 uint32_t blockSize) 00070 { 00071 q15_t *pState = S->pState; /* State pointer */ 00072 q15_t *pCoeffs = S->pCoeffs; /* Coefficient pointer */ 00073 q15_t *pStateCurnt; /* Points to the current sample of the state */ 00074 q15_t *px; /* Temporary pointer for state buffer */ 00075 q15_t *pb; /* Temporary pointer coefficient buffer */ 00076 q31_t x0, c0; /* Temporary variables to hold state and coefficient values */ 00077 q63_t sum0; /* Accumulators */ 00078 uint32_t numTaps = S->numTaps; /* Number of taps */ 00079 uint32_t i, blkCnt, tapCnt, outBlockSize = blockSize / S->M; /* Loop counters */ 00080 00081 #ifndef ARM_MATH_CM0 00082 00083 /* Run the below code for Cortex-M4 and Cortex-M3 */ 00084 00085 /* S->pState buffer contains previous frame (numTaps - 1) samples */ 00086 /* pStateCurnt points to the location where the new input data should be written */ 00087 pStateCurnt = S->pState + (numTaps - 1u); 00088 00089 /* Total number of output samples to be computed */ 00090 blkCnt = outBlockSize; 00091 00092 while(blkCnt > 0u) 00093 { 00094 /* Copy decimation factor number of new input samples into the state buffer */ 00095 i = S->M; 00096 00097 do 00098 { 00099 *pStateCurnt++ = *pSrc++; 00100 00101 } while(--i); 00102 00103 /*Set sum to zero */ 00104 sum0 = 0; 00105 00106 /* Initialize state pointer */ 00107 px = pState; 00108 00109 /* Initialize coeff pointer */ 00110 pb = pCoeffs; 00111 00112 /* Loop unrolling. Process 4 taps at a time. */ 00113 tapCnt = numTaps >> 2; 00114 00115 /* Loop over the number of taps. Unroll by a factor of 4. 00116 ** Repeat until we've computed numTaps-4 coefficients. */ 00117 while(tapCnt > 0u) 00118 { 00119 /* Read the Read b[numTaps-1] and b[numTaps-2] coefficients */ 00120 c0 = *__SIMD32(pb)++; 00121 00122 /* Read x[n-numTaps-1] and x[n-numTaps-2]sample */ 00123 x0 = *__SIMD32(px)++; 00124 00125 /* Perform the multiply-accumulate */ 00126 sum0 = __SMLALD(x0, c0, sum0); 00127 00128 /* Read the b[numTaps-3] and b[numTaps-4] coefficient */ 00129 c0 = *__SIMD32(pb)++; 00130 00131 /* Read x[n-numTaps-2] and x[n-numTaps-3] sample */ 00132 x0 = *__SIMD32(px)++; 00133 00134 /* Perform the multiply-accumulate */ 00135 sum0 = __SMLALD(x0, c0, sum0); 00136 00137 /* Decrement the loop counter */ 00138 tapCnt--; 00139 } 00140 00141 /* If the filter length is not a multiple of 4, compute the remaining filter taps */ 00142 tapCnt = numTaps % 0x4u; 00143 00144 while(tapCnt > 0u) 00145 { 00146 /* Read coefficients */ 00147 c0 = *pb++; 00148 00149 /* Fetch 1 state variable */ 00150 x0 = *px++; 00151 00152 /* Perform the multiply-accumulate */ 00153 sum0 = __SMLALD(x0, c0, sum0); 00154 00155 /* Decrement the loop counter */ 00156 tapCnt--; 00157 } 00158 00159 /* Advance the state pointer by the decimation factor 00160 * to process the next group of decimation factor number samples */ 00161 pState = pState + S->M; 00162 00163 /* Store filter output, smlad returns the values in 2.14 format */ 00164 /* so downsacle by 15 to get output in 1.15 */ 00165 *pDst++ = (q15_t) (__SSAT((sum0 >> 15), 16)); 00166 00167 /* Decrement the loop counter */ 00168 blkCnt--; 00169 } 00170 00171 /* Processing is complete. 00172 ** Now copy the last numTaps - 1 samples to the satrt of the state buffer. 00173 ** This prepares the state buffer for the next function call. */ 00174 00175 /* Points to the start of the state buffer */ 00176 pStateCurnt = S->pState; 00177 00178 i = (numTaps - 1u) >> 2u; 00179 00180 /* copy data */ 00181 while(i > 0u) 00182 { 00183 *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; 00184 *__SIMD32(pStateCurnt)++ = *__SIMD32(pState)++; 00185 00186 /* Decrement the loop counter */ 00187 i--; 00188 } 00189 00190 i = (numTaps - 1u) % 0x04u; 00191 00192 /* copy data */ 00193 while(i > 0u) 00194 { 00195 *pStateCurnt++ = *pState++; 00196 00197 /* Decrement the loop counter */ 00198 i--; 00199 } 00200 00201 #else 00202 00203 /* Run the below code for Cortex-M0 */ 00204 00205 /* S->pState buffer contains previous frame (numTaps - 1) samples */ 00206 /* pStateCurnt points to the location where the new input data should be written */ 00207 pStateCurnt = S->pState + (numTaps - 1u); 00208 00209 /* Total number of output samples to be computed */ 00210 blkCnt = outBlockSize; 00211 00212 while(blkCnt > 0u) 00213 { 00214 /* Copy decimation factor number of new input samples into the state buffer */ 00215 i = S->M; 00216 00217 do 00218 { 00219 *pStateCurnt++ = *pSrc++; 00220 00221 } while(--i); 00222 00223 /*Set sum to zero */ 00224 sum0 = 0; 00225 00226 /* Initialize state pointer */ 00227 px = pState; 00228 00229 /* Initialize coeff pointer */ 00230 pb = pCoeffs; 00231 00232 tapCnt = numTaps; 00233 00234 while(tapCnt > 0u) 00235 { 00236 /* Read coefficients */ 00237 c0 = *pb++; 00238 00239 /* Fetch 1 state variable */ 00240 x0 = *px++; 00241 00242 /* Perform the multiply-accumulate */ 00243 sum0 += (q31_t) x0 *c0; 00244 00245 /* Decrement the loop counter */ 00246 tapCnt--; 00247 } 00248 00249 /* Advance the state pointer by the decimation factor 00250 * to process the next group of decimation factor number samples */ 00251 pState = pState + S->M; 00252 00253 /*Store filter output , smlad will return the values in 2.14 format */ 00254 /* so downsacle by 15 to get output in 1.15 */ 00255 *pDst++ = (q15_t) (__SSAT((sum0 >> 15), 16)); 00256 00257 /* Decrement the loop counter */ 00258 blkCnt--; 00259 } 00260 00261 /* Processing is complete. 00262 ** Now copy the last numTaps - 1 samples to the start of the state buffer. 00263 ** This prepares the state buffer for the next function call. */ 00264 00265 /* Points to the start of the state buffer */ 00266 pStateCurnt = S->pState; 00267 00268 i = numTaps - 1u; 00269 00270 /* copy data */ 00271 while(i > 0u) 00272 { 00273 *pStateCurnt++ = *pState++; 00274 00275 /* Decrement the loop counter */ 00276 i--; 00277 } 00278 00279 #endif /* #ifndef ARM_MATH_CM0 */ 00280 00281 } 00282