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23 #ifndef _ATSC_EQUALIZER_H_
24 #define _ATSC_EQUALIZER_H_
26 #include <atsci_syminfo.h>
29 * \brief abstract base class for ATSC equalizer
31 class atsci_equalizer {
36 * have we seen a field sync since the last reset or problem?
41 * sample offset from the beginning of the last field sync we saw
42 * to the beginning of our current input stream. When we're locked
43 * this will be in [0, 313*832] i.e., [0, 260416]
45 int d_offset_from_last_field_sync;
47 int d_current_field; // [0,1]
54 virtual ~atsci_equalizer ();
59 * \brief reset state (e.g., on channel change)
61 * Note, subclasses must invoke the superclass's method too!
63 virtual void reset ();
66 * \brief produce \p nsamples of output from given inputs and tags
68 * This is the main entry point. It examines the input_tags
69 * and local state and invokes the appropriate virtual function
70 * to handle each sub-segment of the input data.
72 * \p input_samples must have (nsamples + ntaps() - 1) valid entries.
73 * input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] are
74 * referenced to compute the output values.
76 * \p input_tags must have nsamples valid entries.
77 * input_tags[0] .. input_tags[nsamples - 1] are referenced to
78 * compute the output values.
80 virtual void filter (const float *input_samples,
81 const atsc::syminfo *input_tags,
82 float *output_samples,
88 * \brief how much history the input data stream requires.
90 * This must return a value >= 1. Think of this as the number
91 * of samples you need to look at to compute a single output sample.
93 virtual int ntaps () const = 0;
96 * \brief how many taps are "in the future".
98 * This allows us to handle what the ATSC folks call "pre-ghosts".
99 * What it really does is allow the caller to jack with the offset
100 * between the tags and the data so that everything magically works out.
102 * npretaps () must return a value between 0 and ntaps() - 1.
104 * If npretaps () returns 0, this means that the equalizer will only handle
105 * multipath "in the past." I suspect that a good value would be something
106 * like 15% - 20% of ntaps ().
108 virtual int npretaps () const = 0;
114 * Input range is known NOT TO CONTAIN data segment syncs
115 * or field syncs. This should be the fast path. In the
116 * non decicion directed case, this just runs the input
117 * through the filter without adapting it.
119 * \p input_samples has (nsamples + ntaps() - 1) valid entries.
120 * input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be
121 * referenced to compute the output values.
123 virtual void filter_normal (const float *input_samples,
124 float *output_samples,
128 * Input range is known to consist of only a data segment sync or a
129 * portion of a data segment sync. \p nsamples will be in [1,4].
130 * \p offset will be in [0,3]. \p offset is the offset of the input
131 * from the beginning of the data segment sync pattern.
133 * \p input_samples has (nsamples + ntaps() - 1) valid entries.
134 * input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be
135 * referenced to compute the output values.
137 virtual void filter_data_seg_sync (const float *input_samples,
138 float *output_samples,
143 * Input range is known to consist of only a field sync segment or a
144 * portion of a field sync segment. \p nsamples will be in [1,832].
145 * \p offset will be in [0,831]. \p offset is the offset of the input
146 * from the beginning of the data segment sync pattern. We consider the
147 * 4 symbols of the immediately preceding data segment sync to be the
148 * first symbols of the field sync segment. \p which_field is in [0,1]
149 * and specifies which field (duh).
151 * \p input_samples has (nsamples + ntaps() - 1) valid entries.
152 * input_samples[0] .. input_samples[nsamples - 1 + ntaps() - 1] may be
153 * referenced to compute the output values.
155 virtual void filter_field_sync (const float *input_samples,
156 float *output_samples,
159 int which_field) = 0;
163 #endif /* _ATSC_EQUALIZER_H_ */