arm_biquad_cascade_df1_init_q31.c

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_init_q31.c  
00009 *  
00010 * Description:  Q31 Biquad cascade DirectFormI(DF1) filter initialization function.  
00011 *  
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  
00036 /**  
00037  * @ingroup groupFilters  
00038  */ 
00039  
00040 /**  
00041  * @addtogroup BiquadCascadeDF1  
00042  * @{  
00043  */ 
00044  
00045 /**  
00046  * @details  
00047  *  
00048  * @param[in,out] *S           points to an instance of the Q31 Biquad cascade structure.  
00049  * @param[in]     numStages    number of 2nd order stages in the filter.  
00050  * @param[in]     *pCoeffs     points to the filter coefficients buffer.  
00051  * @param[in]     *pState      points to the state buffer.  
00052  * @param[in]     postShift    Shift to be applied after the accumulator.  Varies according to the coefficients format  
00053  * @return        none  
00054  *  
00055  * <b>Coefficient and State Ordering:</b>  
00056  *  
00057  * \par  
00058  * The coefficients are stored in the array <code>pCoeffs</code> in the following order:  
00059  * <pre>  
00060  *     {b10, b11, b12, a11, a12, b20, b21, b22, a21, a22, ...}  
00061  * </pre>  
00062  * where <code>b1x</code> and <code>a1x</code> are the coefficients for the first stage,  
00063  * <code>b2x</code> and <code>a2x</code> are the coefficients for the second stage,  
00064  * and so on.  The <code>pCoeffs</code> array contains a total of <code>5*numStages</code> values.  
00065  *  
00066  * \par  
00067  * The <code>pState</code> points to state variables array.  
00068  * Each Biquad stage has 4 state variables <code>x[n-1], x[n-2], y[n-1],</code> and <code>y[n-2]</code>.  
00069  * The state variables are arranged in the <code>pState</code> array as:  
00070  * <pre>  
00071  *     {x[n-1], x[n-2], y[n-1], y[n-2]}  
00072  * </pre>  
00073  * The 4 state variables for stage 1 are first, then the 4 state variables for stage 2, and so on.  
00074  * The state array has a total length of <code>4*numStages</code> values.  
00075  * The state variables are updated after each block of data is processed; the coefficients are untouched.  
00076  */ 
00077  
00078 void arm_biquad_cascade_df1_init_q31( 
00079   arm_biquad_casd_df1_inst_q31 * S, 
00080   uint8_t numStages, 
00081   q31_t * pCoeffs, 
00082   q31_t * pState, 
00083   int8_t postShift) 
00084 { 
00085   /* Assign filter stages */ 
00086   S->numStages = numStages; 
00087  
00088   /* Assign postShift to be applied to the output */ 
00089   S->postShift = postShift; 
00090  
00091   /* Assign coefficient pointer */ 
00092   S->pCoeffs = pCoeffs; 
00093  
00094   /* Clear state buffer and size is always 4 * numStages */ 
00095   memset(pState, 0, (4u * (uint32_t) numStages) * sizeof(q31_t)); 
00096  
00097   /* Assign state pointer */ 
00098   S->pState = pState; 
00099 } 
00100  
00101 /**  
00102  * @} end of BiquadCascadeDF1 group  
00103  */