1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
|
/* -*- c++ -*- */
/*
* Copyright 2014,2016 Free Software Foundation, Inc.
*
* This file is part of GNU Radio
*
* SPDX-License-Identifier: GPL-3.0-or-later
*
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include "atsc_sync_impl.h"
#include "atsc_types.h"
#include <gnuradio/io_signature.h>
namespace gr {
namespace dtv {
static const double LOOP_FILTER_TAP = 0.0005; // 0.0005 works
static const double ADJUSTMENT_GAIN = 1.0e-5 / (10 * ATSC_DATA_SEGMENT_LENGTH);
static const int SYMBOL_INDEX_OFFSET = 3;
static const int MIN_SEG_LOCK_CORRELATION_VALUE = 5;
static const signed char SSI_MIN = -16;
static const signed char SSI_MAX = 15;
atsc_sync::sptr atsc_sync::make(float rate)
{
return gnuradio::make_block_sptr<atsc_sync_impl>(rate);
}
atsc_sync_impl::atsc_sync_impl(float rate)
: gr::block("dtv_atsc_sync",
io_signature::make(1, 1, sizeof(float)),
io_signature::make(1, 1, ATSC_DATA_SEGMENT_LENGTH * sizeof(float))),
d_rx_clock_to_symbol_freq(rate / ATSC_SYMBOL_RATE),
d_si(0)
{
d_loop.set_taps(LOOP_FILTER_TAP);
reset();
}
void atsc_sync_impl::reset()
{
d_w = d_rx_clock_to_symbol_freq;
d_mu = 0.5;
d_timing_adjust = 0;
d_counter = 0;
d_symbol_index = 0;
d_seg_locked = false;
d_sr = 0;
memset(d_sample_mem,
0,
ATSC_DATA_SEGMENT_LENGTH * sizeof(*d_sample_mem)); // (float)0 = 0x00000000
memset(d_data_mem,
0,
ATSC_DATA_SEGMENT_LENGTH * sizeof(*d_data_mem)); // (float)0 = 0x00000000
memset(d_integrator,
SSI_MIN,
ATSC_DATA_SEGMENT_LENGTH * sizeof(*d_integrator)); // signed char
}
atsc_sync_impl::~atsc_sync_impl() {}
void atsc_sync_impl::forecast(int noutput_items, gr_vector_int& ninput_items_required)
{
unsigned ninputs = ninput_items_required.size();
for (unsigned i = 0; i < ninputs; i++)
ninput_items_required[i] =
static_cast<int>(noutput_items * d_rx_clock_to_symbol_freq *
ATSC_DATA_SEGMENT_LENGTH) +
1500 - 1;
}
int atsc_sync_impl::general_work(int noutput_items,
gr_vector_int& ninput_items,
gr_vector_const_void_star& input_items,
gr_vector_void_star& output_items)
{
const float* in = static_cast<const float*>(input_items[0]);
float* out = static_cast<float*>(output_items[0]);
float interp_sample;
// amount actually consumed
d_si = 0;
for (d_output_produced = 0; d_output_produced < noutput_items &&
(d_si + (int)d_interp.ntaps()) < ninput_items[0];) {
// First we interpolate a sample from input to work with
interp_sample = d_interp.interpolate(&in[d_si], d_mu);
// Apply our timing adjustment slowly over several samples
d_mu += ADJUSTMENT_GAIN * 1e3 * d_timing_adjust;
double s = d_mu + d_w;
double float_incr = floor(s);
d_mu = s - float_incr;
d_incr = (int)float_incr;
assert(d_incr >= 1 && d_incr <= 3);
d_si += d_incr;
// Remember the sample at this count position
d_sample_mem[d_counter] = interp_sample;
// Is the sample positive or negative?
int bit = (interp_sample < 0 ? 0 : 1);
// Put the sign bit into our shift register
d_sr = ((bit & 1) << 3) | (d_sr >> 1);
// When +,-,-,+ (0x9, 1001) samples show up we have likely found a segment
// sync, it is more likely the segment sync will show up at about the same
// spot every ATSC_DATA_SEGMENT_LENGTH samples so we add some weight
// to this spot every pass to prevent random +,-,-,+ symbols from
// confusing our synchronizer
d_integrator[d_counter] += ((d_sr == 0x9) ? +2 : -1);
if (d_integrator[d_counter] < SSI_MIN)
d_integrator[d_counter] = SSI_MIN;
if (d_integrator[d_counter] > SSI_MAX)
d_integrator[d_counter] = SSI_MAX;
d_symbol_index++;
if (d_symbol_index >= ATSC_DATA_SEGMENT_LENGTH)
d_symbol_index = 0;
d_counter++;
if (d_counter >= ATSC_DATA_SEGMENT_LENGTH) { // counter just wrapped...
int best_correlation_value = d_integrator[0];
int best_correlation_index = 0;
for (int i = 1; i < ATSC_DATA_SEGMENT_LENGTH; i++)
if (d_integrator[i] > best_correlation_value) {
best_correlation_value = d_integrator[i];
best_correlation_index = i;
}
d_seg_locked = best_correlation_value >= MIN_SEG_LOCK_CORRELATION_VALUE;
// the coefficients are -1,-1,+1,+1
// d_timing_adjust = d_sample_mem[best_correlation_index - 3] +
// d_sample_mem[best_correlation_index - 2] -
// d_sample_mem[best_correlation_index - 1] -
// d_sample_mem[best_correlation_index];
int corr_count = best_correlation_index;
d_timing_adjust = -d_sample_mem[corr_count--];
if (corr_count < 0)
corr_count = ATSC_DATA_SEGMENT_LENGTH - 1;
d_timing_adjust -= d_sample_mem[corr_count--];
if (corr_count < 0)
corr_count = ATSC_DATA_SEGMENT_LENGTH - 1;
d_timing_adjust += d_sample_mem[corr_count--];
if (corr_count < 0)
corr_count = ATSC_DATA_SEGMENT_LENGTH - 1;
d_timing_adjust += d_sample_mem[corr_count--];
d_symbol_index = SYMBOL_INDEX_OFFSET - 1 - best_correlation_index;
if (d_symbol_index < 0)
d_symbol_index += ATSC_DATA_SEGMENT_LENGTH;
d_counter = 0;
}
// If we are locked we can start filling and producing data packets
// Due to the way we lock the first data packet will almost always be
// half full, this is OK because the fs_checker will not let packets though
// until a non-corrupted field packet is found
if (d_seg_locked) {
d_data_mem[d_symbol_index] = interp_sample;
if (d_symbol_index >= (ATSC_DATA_SEGMENT_LENGTH - 1)) {
memcpy(&out[d_output_produced * ATSC_DATA_SEGMENT_LENGTH],
d_data_mem,
ATSC_DATA_SEGMENT_LENGTH * sizeof(float));
d_output_produced++;
}
}
}
consume_each(d_si);
return d_output_produced;
}
} /* namespace dtv */
} /* namespace gr */
|
