teensy-audio/filter_fir.h

/* Audio Library for Teensy 3.X
 * Copyright (c) 2014, Pete (El Supremo)
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#ifndef filter_fir_h_
#define filter_fir_h_

#include "AudioStream.h"
#include "arm_math.h"

#define USE_FAST_FIR true
#define USE_SLOW_FIR false


// Maximum number of coefficients in a FIR filter
// The audio breaks up with 128 coefficients so a
// maximum of 150 is more than sufficient
#define MAX_COEFFS 150

// Indicates that the code should just pass through the audio
// without any filtering (as opposed to doing nothing at all)
#define FIR_PASSTHRU ((short *) 1)

class AudioFilterFIR : 
public AudioStream
{
public:
  AudioFilterFIR(const boolean a_f): 
  AudioStream(2,inputQueueArray), arm_fast(a_f), coeff_p(NULL)
  { 
  }

  void begin(short *coeff_p,int n_coeffs);
  virtual void update(void);
  void stop(void);
  
private:
  audio_block_t *inputQueueArray[2];
  // arm state arrays and FIR instances for left and right channels
  // the state arrays are defined to handle a maximum of MAX_COEFFS
  // coefficients in a filter
  q15_t l_StateQ15[AUDIO_BLOCK_SAMPLES + MAX_COEFFS];
  arm_fir_instance_q15 l_fir_inst;
  // pointer to current coefficients or NULL or FIR_PASSTHRU
  short *coeff_p;
  // Whether to use the fast arm FIR code 
  const boolean arm_fast;
};

#endif