Diff: cmsis_dsp/FilteringFunctions/arm_biquad_cascade_df1_32x64_q31.c

Revision:

1:fdd22bb7aa52

Child:

2:da51fb522205

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/cmsis_dsp/FilteringFunctions/arm_biquad_cascade_df1_32x64_q31.c	Wed Nov 28 12:30:09 2012 +0000
@@ -0,0 +1,553 @@
+/* ----------------------------------------------------------------------    
+* Copyright (C) 2010 ARM Limited. All rights reserved.    
+*    
+* $Date:        15. February 2012  
+* $Revision:     V1.1.0  
+*    
+* Project:         CMSIS DSP Library    
+* Title:        arm_biquad_cascade_df1_32x64_q31.c    
+*    
+* Description:    High precision Q31 Biquad cascade filter processing function    
+*    
+* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
+*  
+* Version 1.1.0 2012/02/15 
+*    Updated with more optimizations, bug fixes and minor API changes.  
+*   
+* Version 1.0.10 2011/7/15  
+*    Big Endian support added and Merged M0 and M3/M4 Source code.   
+*    
+* 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.    
+*    
+* Version 0.0.7  2010/06/10     
+*    Misra-C changes done    
+* -------------------------------------------------------------------- */
+
+#include "arm_math.h"
+
+/**    
+ * @ingroup groupFilters    
+ */
+
+/**    
+ * @defgroup BiquadCascadeDF1_32x64 High Precision Q31 Biquad Cascade Filter    
+ *    
+ * This function implements a high precision Biquad cascade filter which operates on    
+ * Q31 data values.  The filter coefficients are in 1.31 format and the state variables    
+ * are in 1.63 format.  The double precision state variables reduce quantization noise    
+ * in the filter and provide a cleaner output.    
+ * These filters are particularly useful when implementing filters in which the    
+ * singularities are close to the unit circle.  This is common for low pass or high    
+ * pass filters with very low cutoff frequencies.    
+ *    
+ * The function operates on blocks of input and output data    
+ * and each call to the function processes <code>blockSize</code> samples through    
+ * the filter. <code>pSrc</code> and <code>pDst</code> points to input and output arrays    
+ * containing <code>blockSize</code> Q31 values.    
+ *    
+ * \par Algorithm    
+ * Each Biquad stage implements a second order filter using the difference equation:    
+ * <pre>    
+ *     y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]    
+ * </pre>    
+ * A Direct Form I algorithm is used with 5 coefficients and 4 state variables per stage.    
+ * \image html Biquad.gif "Single Biquad filter stage"    
+ * Coefficients <code>b0, b1, and b2 </code> multiply the input signal <code>x[n]</code> and are referred to as the feedforward coefficients.    
+ * Coefficients <code>a1</code> and <code>a2</code> multiply the output signal <code>y[n]</code> and are referred to as the feedback coefficients.    
+ * Pay careful attention to the sign of the feedback coefficients.    
+ * Some design tools use the difference equation    
+ * <pre>    
+ *     y[n] = b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] - a1 * y[n-1] - a2 * y[n-2]    
+ * </pre>    
+ * In this case the feedback coefficients <code>a1</code> and <code>a2</code> must be negated when used with the CMSIS DSP Library.    
+ *    
+ * \par    
+ * Higher order filters are realized as a cascade of second order sections.    
+ * <code>numStages</code> refers to the number of second order stages used.    
+ * For example, an 8th order filter would be realized with <code>numStages=4</code> second order stages.    
+ * \image html BiquadCascade.gif "8th order filter using a cascade of Biquad stages"    
+ * A 9th order filter would be realized with <code>numStages=5</code> second order stages with the coefficients for one of the stages configured as a first order filter (<code>b2=0</code> and <code>a2=0</code>).    
+ *    
+ * \par    
+ * The <code>pState</code> points to state variables array .    
+ * Each Biquad stage has 4 state variables <code>x[n-1], x[n-2], y[n-1],</code> and <code>y[n-2]</code> and each state variable in 1.63 format to improve precision.    
+ * The state variables are arranged in the array as:    
+ * <pre>    
+ *     {x[n-1], x[n-2], y[n-1], y[n-2]}    
+ * </pre>    
+ *    
+ * \par    
+ * The 4 state variables for stage 1 are first, then the 4 state variables for stage 2, and so on.    
+ * The state array has a total length of <code>4*numStages</code> values of data in 1.63 format.    
+ * The state variables are updated after each block of data is processed; the coefficients are untouched.    
+ *    
+ * \par Instance Structure    
+ * The coefficients and state variables for a filter are stored together in an instance data structure.    
+ * A separate instance structure must be defined for each filter.    
+ * Coefficient arrays may be shared among several instances while state variable arrays cannot be shared.    
+ *    
+ * \par Init Function    
+ * There is also an associated initialization function which performs the following operations:    
+ * - Sets the values of the internal structure fields.    
+ * - Zeros out the values in the state buffer.    
+ * \par    
+ * Use of the initialization function is optional.    
+ * However, if the initialization function is used, then the instance structure cannot be placed into a const data section.    
+ * To place an instance structure into a const data section, the instance structure must be manually initialized.    
+ * Set the values in the state buffer to zeros before static initialization.    
+ * For example, to statically initialize the filter instance structure use    
+ * <pre>    
+ *     arm_biquad_cas_df1_32x64_ins_q31 S1 = {numStages, pState, pCoeffs, postShift};    
+ * </pre>    
+ * where <code>numStages</code> is the number of Biquad stages in the filter; <code>pState</code> is the address of the state buffer;    
+ * <code>pCoeffs</code> is the address of the coefficient buffer; <code>postShift</code> shift to be applied which is described in detail below.    
+ * \par Fixed-Point Behavior    
+ * Care must be taken while using Biquad Cascade 32x64 filter function.    
+ * Following issues must be considered:    
+ * - Scaling of coefficients    
+ * - Filter gain    
+ * - Overflow and saturation    
+ *    
+ * \par    
+ * Filter coefficients are represented as fractional values and    
+ * restricted to lie in the range <code>[-1 +1)</code>.    
+ * The processing function has an additional scaling parameter <code>postShift</code>    
+ * which allows the filter coefficients to exceed the range <code>[+1 -1)</code>.    
+ * At the output of the filter's accumulator is a shift register which shifts the result by <code>postShift</code> bits.    
+ * \image html BiquadPostshift.gif "Fixed-point Biquad with shift by postShift bits after accumulator"    
+ * This essentially scales the filter coefficients by <code>2^postShift</code>.    
+ * For example, to realize the coefficients    
+ * <pre>    
+ *    {1.5, -0.8, 1.2, 1.6, -0.9}    
+ * </pre>    
+ * set the Coefficient array to:    
+ * <pre>    
+ *    {0.75, -0.4, 0.6, 0.8, -0.45}    
+ * </pre>    
+ * and set <code>postShift=1</code>    
+ *    
+ * \par    
+ * The second thing to keep in mind is the gain through the filter.    
+ * The frequency response of a Biquad filter is a function of its coefficients.    
+ * It is possible for the gain through the filter to exceed 1.0 meaning that the filter increases the amplitude of certain frequencies.    
+ * This means that an input signal with amplitude < 1.0 may result in an output > 1.0 and these are saturated or overflowed based on the implementation of the filter.    
+ * To avoid this behavior the filter needs to be scaled down such that its peak gain < 1.0 or the input signal must be scaled down so that the combination of input and filter are never overflowed.    
+ *    
+ * \par    
+ * The third item to consider is the overflow and saturation behavior of the fixed-point Q31 version.    
+ * This is described in the function specific documentation below.    
+ */
+
+/**    
+ * @addtogroup BiquadCascadeDF1_32x64    
+ * @{    
+ */
+
+/**    
+ * @details    
+    
+ * @param[in]  *S points to an instance of the high precision Q31 Biquad cascade filter.    
+ * @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.    
+ * @return none.    
+ *    
+ * \par    
+ * The function is implemented using an internal 64-bit accumulator.    
+ * The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.    
+ * Thus, if the accumulator result overflows it wraps around rather than clip.    
+ * In order to avoid overflows completely the input signal must be scaled down by 2 bits and lie in the range [-0.25 +0.25).    
+ * After all 5 multiply-accumulates are performed, the 2.62 accumulator is shifted by <code>postShift</code> bits and the result truncated to    
+ * 1.31 format by discarding the low 32 bits.    
+ *    
+ * \par    
+ * Two related functions are provided in the CMSIS DSP library.    
+ * <code>arm_biquad_cascade_df1_q31()</code> implements a Biquad cascade with 32-bit coefficients and state variables with a Q63 accumulator.    
+ * <code>arm_biquad_cascade_df1_fast_q31()</code> implements a Biquad cascade with 32-bit coefficients and state variables with a Q31 accumulator.    
+ */
+
+void arm_biquad_cas_df1_32x64_q31(
+  const arm_biquad_cas_df1_32x64_ins_q31 * S,
+  q31_t * pSrc,
+  q31_t * pDst,
+  uint32_t blockSize)
+{
+  q31_t *pIn = pSrc;                             /*  input pointer initialization  */
+  q31_t *pOut = pDst;                            /*  output pointer initialization */
+  q63_t *pState = S->pState;                     /*  state pointer initialization  */
+  q31_t *pCoeffs = S->pCoeffs;                   /*  coeff pointer initialization  */
+  q63_t acc;                                     /*  accumulator                   */
+  q31_t Xn1, Xn2;                                /*  Input Filter state variables        */
+  q63_t Yn1, Yn2;                                /*  Output Filter state variables        */
+  q31_t b0, b1, b2, a1, a2;                      /*  Filter coefficients           */
+  q31_t Xn;                                      /*  temporary input               */
+  int32_t shift = (int32_t) S->postShift + 1;    /*  Shift to be applied to the output */
+  uint32_t sample, stage = S->numStages;         /*  loop counters                     */
+  q31_t acc_l, acc_h;                            /*  temporary output               */
+  uint32_t uShift = ((uint32_t) S->postShift + 1u);
+  uint32_t lShift = 32u - uShift;                /*  Shift to be applied to the output */
+
+
+#ifndef ARM_MATH_CM0
+
+  /* Run the below code for Cortex-M4 and Cortex-M3 */
+
+  do
+  {
+    /* Reading the coefficients */
+    b0 = *pCoeffs++;
+    b1 = *pCoeffs++;
+    b2 = *pCoeffs++;
+    a1 = *pCoeffs++;
+    a2 = *pCoeffs++;
+
+    /* Reading the state values */
+    Xn1 = (q31_t) (pState[0]);
+    Xn2 = (q31_t) (pState[1]);
+    Yn1 = pState[2];
+    Yn2 = pState[3];
+
+    /* Apply loop unrolling and compute 4 output values simultaneously. */
+    /* The variable acc hold output value that is being computed and    
+     * stored in the destination buffer    
+     * acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]    
+     */
+
+    sample = blockSize >> 2u;
+
+    /* 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(sample > 0u)
+    {
+      /* Read the input */
+      Xn = *pIn++;
+
+      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
+
+      /* acc =  b0 * x[n] */
+      acc = (q63_t) Xn *b0;
+
+      /* acc +=  b1 * x[n-1] */
+      acc += (q63_t) Xn1 *b1;
+
+      /* acc +=  b[2] * x[n-2] */
+      acc += (q63_t) Xn2 *b2;
+
+      /* acc +=  a1 * y[n-1] */
+      acc += mult32x64(Yn1, a1);
+
+      /* acc +=  a2 * y[n-2] */
+      acc += mult32x64(Yn2, a2);
+
+      /* The result is converted to 1.63 , Yn2 variable is reused */
+      Yn2 = acc << shift;
+
+      /* Calc lower part of acc */
+      acc_l = acc & 0xffffffff;
+
+      /* Calc upper part of acc */
+      acc_h = (acc >> 32) & 0xffffffff;
+
+      /* Apply shift for lower part of acc and upper part of acc */
+      acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift;
+
+      /* Store the output in the destination buffer in 1.31 format. */
+      *pOut = acc_h;
+
+      /* Read the second input into Xn2, to reuse the value */
+      Xn2 = *pIn++;
+
+      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
+
+      /* acc +=  b1 * x[n-1] */
+      acc = (q63_t) Xn *b1;
+
+      /* acc =  b0 * x[n] */
+      acc += (q63_t) Xn2 *b0;
+
+      /* acc +=  b[2] * x[n-2] */
+      acc += (q63_t) Xn1 *b2;
+
+      /* acc +=  a1 * y[n-1] */
+      acc += mult32x64(Yn2, a1);
+
+      /* acc +=  a2 * y[n-2] */
+      acc += mult32x64(Yn1, a2);
+
+      /* The result is converted to 1.63, Yn1 variable is reused */
+      Yn1 = acc << shift;
+
+      /* Calc lower part of acc */
+      acc_l = acc & 0xffffffff;
+
+      /* Calc upper part of acc */
+      acc_h = (acc >> 32) & 0xffffffff;
+
+      /* Apply shift for lower part of acc and upper part of acc */
+      acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift;
+
+      /* Read the third input into Xn1, to reuse the value */
+      Xn1 = *pIn++;
+
+      /* The result is converted to 1.31 */
+      /* Store the output in the destination buffer. */
+      *(pOut + 1u) = acc_h;
+
+      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
+
+      /* acc =  b0 * x[n] */
+      acc = (q63_t) Xn1 *b0;
+
+      /* acc +=  b1 * x[n-1] */
+      acc += (q63_t) Xn2 *b1;
+
+      /* acc +=  b[2] * x[n-2] */
+      acc += (q63_t) Xn *b2;
+
+      /* acc +=  a1 * y[n-1] */
+      acc += mult32x64(Yn1, a1);
+
+      /* acc +=  a2 * y[n-2] */
+      acc += mult32x64(Yn2, a2);
+
+      /* The result is converted to 1.63, Yn2 variable is reused  */
+      Yn2 = acc << shift;
+
+      /* Calc lower part of acc */
+      acc_l = acc & 0xffffffff;
+
+      /* Calc upper part of acc */
+      acc_h = (acc >> 32) & 0xffffffff;
+
+      /* Apply shift for lower part of acc and upper part of acc */
+      acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift;
+
+      /* Store the output in the destination buffer in 1.31 format. */
+      *(pOut + 2u) = acc_h;
+
+      /* Read the fourth input into Xn, to reuse the value */
+      Xn = *pIn++;
+
+      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
+      /* acc =  b0 * x[n] */
+      acc = (q63_t) Xn *b0;
+
+      /* acc +=  b1 * x[n-1] */
+      acc += (q63_t) Xn1 *b1;
+
+      /* acc +=  b[2] * x[n-2] */
+      acc += (q63_t) Xn2 *b2;
+
+      /* acc +=  a1 * y[n-1] */
+      acc += mult32x64(Yn2, a1);
+
+      /* acc +=  a2 * y[n-2] */
+      acc += mult32x64(Yn1, a2);
+
+      /* The result is converted to 1.63, Yn1 variable is reused  */
+      Yn1 = acc << shift;
+
+      /* Calc lower part of acc */
+      acc_l = acc & 0xffffffff;
+
+      /* Calc upper part of acc */
+      acc_h = (acc >> 32) & 0xffffffff;
+
+      /* Apply shift for lower part of acc and upper part of acc */
+      acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift;
+
+      /* Store the output in the destination buffer in 1.31 format. */
+      *(pOut + 3u) = acc_h;
+
+      /* Every time after the output is computed state should be updated. */
+      /* The states should be updated as:  */
+      /* Xn2 = Xn1    */
+      /* Xn1 = Xn     */
+      /* Yn2 = Yn1    */
+      /* Yn1 = acc    */
+      Xn2 = Xn1;
+      Xn1 = Xn;
+
+      /* update output pointer */
+      pOut += 4u;
+
+      /* decrement the loop counter */
+      sample--;
+    }
+
+    /* If the blockSize is not a multiple of 4, compute any remaining output samples here.    
+     ** No loop unrolling is used. */
+    sample = (blockSize & 0x3u);
+
+    while(sample > 0u)
+    {
+      /* Read the input */
+      Xn = *pIn++;
+
+      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
+
+      /* acc =  b0 * x[n] */
+      acc = (q63_t) Xn *b0;
+      /* acc +=  b1 * x[n-1] */
+      acc += (q63_t) Xn1 *b1;
+      /* acc +=  b[2] * x[n-2] */
+      acc += (q63_t) Xn2 *b2;
+      /* acc +=  a1 * y[n-1] */
+      acc += mult32x64(Yn1, a1);
+      /* acc +=  a2 * y[n-2] */
+      acc += mult32x64(Yn2, a2);
+
+      /* Every time after the output is computed state should be updated. */
+      /* The states should be updated as:  */
+      /* Xn2 = Xn1    */
+      /* Xn1 = Xn     */
+      /* Yn2 = Yn1    */
+      /* Yn1 = acc    */
+      Xn2 = Xn1;
+      Xn1 = Xn;
+      Yn2 = Yn1;
+      /* The result is converted to 1.63, Yn1 variable is reused  */
+      Yn1 = acc << shift;
+
+      /* Calc lower part of acc */
+      acc_l = acc & 0xffffffff;
+
+      /* Calc upper part of acc */
+      acc_h = (acc >> 32) & 0xffffffff;
+
+      /* Apply shift for lower part of acc and upper part of acc */
+      acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift;
+
+      /* Store the output in the destination buffer in 1.31 format. */
+      *pOut++ = acc_h;
+      //Yn1 = acc << shift; 
+
+      /* Store the output in the destination buffer in 1.31 format. */
+//      *pOut++ = (q31_t) (acc >> (32 - shift)); 
+
+      /* decrement the loop counter */
+      sample--;
+    }
+
+    /*  The first stage output is given as input to the second stage. */
+    pIn = pDst;
+
+    /* Reset to destination buffer working pointer */
+    pOut = pDst;
+
+    /*  Store the updated state variables back into the pState array */
+    /*  Store the updated state variables back into the pState array */
+    *pState++ = (q63_t) Xn1;
+    *pState++ = (q63_t) Xn2;
+    *pState++ = Yn1;
+    *pState++ = Yn2;
+
+  } while(--stage);
+
+#else
+
+  /* Run the below code for Cortex-M0 */
+
+  do
+  {
+    /* Reading the coefficients */
+    b0 = *pCoeffs++;
+    b1 = *pCoeffs++;
+    b2 = *pCoeffs++;
+    a1 = *pCoeffs++;
+    a2 = *pCoeffs++;
+
+    /* Reading the state values */
+    Xn1 = pState[0];
+    Xn2 = pState[1];
+    Yn1 = pState[2];
+    Yn2 = pState[3];
+
+    /* The variable acc hold output value that is being computed and        
+     * stored in the destination buffer            
+     * acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2]            
+     */
+
+    sample = blockSize;
+
+    while(sample > 0u)
+    {
+      /* Read the input */
+      Xn = *pIn++;
+
+      /* acc =  b0 * x[n] + b1 * x[n-1] + b2 * x[n-2] + a1 * y[n-1] + a2 * y[n-2] */
+      /* acc =  b0 * x[n] */
+      acc = (q63_t) Xn *b0;
+      /* acc +=  b1 * x[n-1] */
+      acc += (q63_t) Xn1 *b1;
+      /* acc +=  b[2] * x[n-2] */
+      acc += (q63_t) Xn2 *b2;
+      /* acc +=  a1 * y[n-1] */
+      acc += mult32x64(Yn1, a1);
+      /* acc +=  a2 * y[n-2] */
+      acc += mult32x64(Yn2, a2);
+
+      /* Every time after the output is computed state should be updated. */
+      /* The states should be updated as:  */
+      /* Xn2 = Xn1    */
+      /* Xn1 = Xn     */
+      /* Yn2 = Yn1    */
+      /* Yn1 = acc    */
+      Xn2 = Xn1;
+      Xn1 = Xn;
+      Yn2 = Yn1;
+
+      /* The result is converted to 1.63, Yn1 variable is reused  */
+      Yn1 = acc << shift;
+
+      /* Calc lower part of acc */
+      acc_l = acc & 0xffffffff;
+
+      /* Calc upper part of acc */
+      acc_h = (acc >> 32) & 0xffffffff;
+
+      /* Apply shift for lower part of acc and upper part of acc */
+      acc_h = (uint32_t) acc_l >> lShift | acc_h << uShift;
+
+      /* Store the output in the destination buffer in 1.31 format. */
+      *pOut++ = acc_h;
+
+      //Yn1 = acc << shift; 
+
+      /* Store the output in the destination buffer in 1.31 format. */
+      //*pOut++ = (q31_t) (acc >> (32 - shift)); 
+
+      /* decrement the loop counter */
+      sample--;
+    }
+
+    /*  The first stage output is given as input to the second stage. */
+    pIn = pDst;
+
+    /* Reset to destination buffer working pointer */
+    pOut = pDst;
+
+    /*  Store the updated state variables back into the pState array */
+    *pState++ = (q63_t) Xn1;
+    *pState++ = (q63_t) Xn2;
+    *pState++ = Yn1;
+    *pState++ = Yn2;
+
+  } while(--stage);
+
+#endif /*    #ifndef ARM_MATH_CM0     */
+}
+
+  /**    
+   * @} end of BiquadCascadeDF1_32x64 group    
+   */