- 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::get_initial_sptr

- (new 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, sizeof(atsc_soft_data_segment))),

- 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 = (const float *) input_items[0];

- atsc_soft_data_segment *soft_data_segment_out = (atsc_soft_data_segment *) 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_counter++;

- if( d_counter >= ATSC_DATA_SEGMENT_LENGTH ) { // counter just wrapped...

- 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_timing_adjust = d_sample_mem[best_correlation_index - 3] +

- //printf( "d_timing_adjust = %f\n", d_timing_adjust );

- if( corr_count < 0 ) corr_count = ATSC_DATA_SEGMENT_LENGTH - 1;

- if( corr_count < 0 ) corr_count = ATSC_DATA_SEGMENT_LENGTH - 1;

- if( corr_count < 0 ) corr_count = ATSC_DATA_SEGMENT_LENGTH - 1;

- d_symbol_index += ATSC_DATA_SEGMENT_LENGTH;

- }

- // 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 ) {

- if( d_symbol_index >= (ATSC_DATA_SEGMENT_LENGTH - 1) )

- {

- for( int i = 0; i < ATSC_DATA_SEGMENT_LENGTH; i++ )

- soft_data_segment_out[d_output_produced].data[i] = d_data_mem[i];

- }

- }

- }

-

- consume_each(d_si);

- return d_output_produced;

-

- } /* namespace dtv */