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/* -*- c++ -*- */
/*
* Copyright 2002 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* GNU Radio is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2, or (at your option)
* any later version.
*
* GNU Radio is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with GNU Radio; see the file COPYING. If not, write to
* the Free Software Foundation, Inc., 51 Franklin Street,
* Boston, MA 02110-1301, USA.
*/
#ifndef _ATSC_EQUALIZER_H_
#define _ATSC_EQUALIZER_H_
#include <atsci_syminfo.h>
/*!
* \brief abstract base class for ATSC equalizer
*/
class atsci_equalizer {
private:
/*
* have we seen a field sync since the last reset or problem?
*/
bool d_locked_p;
/*
* sample offset from the beginning of the last field sync we saw
* to the beginning of our current input stream. When we're locked
* this will be in [0, 313*832] i.e., [0, 260416]
*/
int d_offset_from_last_field_sync;
int d_current_field; // [0,1]
public:
// CREATORS
atsci_equalizer ();
virtual ~atsci_equalizer ();
// MANIPULATORS
/*!
* \brief reset state (e.g., on channel change)
*
* Note, subclasses must invoke the superclass's method too!
*/
virtual void reset ();
/*!
* \brief produce \p nsamples of output from given inputs and tags
*
* This is the main entry point. It examines the input_tags
* and local state and invokes the appropriate virtual function
* to handle each sub-segment of the input data.
*
* \p input_samples must have (nsamples + ntaps() - 1) valid entries.
* input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] are
* referenced to compute the output values.
*
* \p input_tags must have nsamples valid entries.
* input_tags[0] .. input_tags[nsamples - 1] are referenced to
* compute the output values.
*/
virtual void filter (const float *input_samples,
const atsc::syminfo *input_tags,
float *output_samples,
int nsamples);
// ACCESSORS
/*!
* \brief how much history the input data stream requires.
*
* This must return a value >= 1. Think of this as the number
* of samples you need to look at to compute a single output sample.
*/
virtual int ntaps () const = 0;
/*!
* \brief how many taps are "in the future".
*
* This allows us to handle what the ATSC folks call "pre-ghosts".
* What it really does is allow the caller to jack with the offset
* between the tags and the data so that everything magically works out.
*
* npretaps () must return a value between 0 and ntaps() - 1.
*
* If npretaps () returns 0, this means that the equalizer will only handle
* multipath "in the past." I suspect that a good value would be something
* like 15% - 20% of ntaps ().
*/
virtual int npretaps () const = 0;
protected:
/*!
* Input range is known NOT TO CONTAIN data segment syncs
* or field syncs. This should be the fast path. In the
* non decicion directed case, this just runs the input
* through the filter without adapting it.
*
* \p input_samples has (nsamples + ntaps() - 1) valid entries.
* input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be
* referenced to compute the output values.
*/
virtual void filter_normal (const float *input_samples,
float *output_samples,
int nsamples) = 0;
/*!
* Input range is known to consist of only a data segment sync or a
* portion of a data segment sync. \p nsamples will be in [1,4].
* \p offset will be in [0,3]. \p offset is the offset of the input
* from the beginning of the data segment sync pattern.
*
* \p input_samples has (nsamples + ntaps() - 1) valid entries.
* input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be
* referenced to compute the output values.
*/
virtual void filter_data_seg_sync (const float *input_samples,
float *output_samples,
int nsamples,
int offset) = 0;
/*!
* Input range is known to consist of only a field sync segment or a
* portion of a field sync segment. \p nsamples will be in [1,832].
* \p offset will be in [0,831]. \p offset is the offset of the input
* from the beginning of the data segment sync pattern. We consider the
* 4 symbols of the immediately preceding data segment sync to be the
* first symbols of the field sync segment. \p which_field is in [0,1]
* and specifies which field (duh).
*
* \p input_samples has (nsamples + ntaps() - 1) valid entries.
* input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be
* referenced to compute the output values.
*/
virtual void filter_field_sync (const float *input_samples,
float *output_samples,
int nsamples,
int offset,
int which_field) = 0;
};
#endif /* _ATSC_EQUALIZER_H_ */
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