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/* -*- c++ -*- */
/*
* Copyright 2004,2010,2013 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 3, 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.
*/
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <digital_simple_correlator.h>
#include <digital_simple_framer_sync.h>
#include <gr_io_signature.h>
#include <gr_count_bits.h>
#include <assert.h>
#include <stdexcept>
#include <string.h>
#include <cstdio>
static const int THRESHOLD = 3;
digital_simple_correlator_sptr
digital_make_simple_correlator(int payload_bytesize)
{
return gnuradio::get_initial_sptr
(new digital_simple_correlator(payload_bytesize));
}
digital_simple_correlator::digital_simple_correlator(int payload_bytesize)
: gr_block("simple_correlator",
gr_make_io_signature(1, 1, sizeof(float)),
gr_make_io_signature(1, 1, sizeof(unsigned char))),
d_payload_bytesize(payload_bytesize),
d_state(ST_LOOKING), d_osi(0),
d_bblen((payload_bytesize + GRSF_PAYLOAD_OVERHEAD) * GRSF_BITS_PER_BYTE),
d_bitbuf(new unsigned char[d_bblen]),
d_pktbuf(new unsigned char[d_bblen/GRSF_BITS_PER_BYTE]),
d_bbi(0)
{
d_avbi = 0;
d_accum = 0.0;
d_avg = 0.0;
for(int i = 0; i < AVG_PERIOD; i++)
d_avgbuf[i] = 0.0;
#ifdef DEBUG_SIMPLE_CORRELATOR
d_debug_fp = fopen("corr.log", "w");
#endif
enter_looking();
}
digital_simple_correlator::~digital_simple_correlator()
{
#ifdef DEBUG_SIMPLE_CORRELATOR
fclose(d_debug_fp);
#endif
delete [] d_bitbuf;
delete [] d_pktbuf;
}
void
digital_simple_correlator::enter_looking()
{
fflush(stdout);
// fprintf(stderr, ">>> enter_looking\n");
d_state = ST_LOOKING;
for(int i = 0; i < OVERSAMPLE; i++)
d_shift_reg[i] = 0;
d_osi = 0;
d_avbi = 0;
d_avg = d_avg * 0.5;
d_accum = 0;
for(int i = 0; i < AVG_PERIOD; i++)
d_avgbuf[i] = 0.0;
}
void
digital_simple_correlator::enter_under_threshold()
{
fflush(stdout);
// fprintf(stderr, ">>> enter_under_threshold\n");
d_state = ST_UNDER_THRESHOLD;
d_transition_osi = d_osi;
}
void
digital_simple_correlator::enter_locked()
{
d_state = ST_LOCKED;
int delta = sub_index(d_osi, d_transition_osi);
d_center_osi = add_index(d_transition_osi, delta/2);
//d_center_osi = add_index(d_center_osi, 3); // FIXME
d_bbi = 0;
fflush(stdout);
// fprintf(stderr, ">>> enter_locked d_center_osi = %d\n", d_center_osi);
d_avg = std::max(-1.0, std::min(1.0, d_accum * (1.0/AVG_PERIOD)));
// fprintf(stderr, ">>> enter_locked d_avg = %g\n", d_avg);
}
static void
packit(unsigned char *pktbuf, const unsigned char *bitbuf, int bitcount)
{
for(int i = 0; i < bitcount; i += 8) {
int t = bitbuf[i+0] & 0x1;
t = (t << 1) | (bitbuf[i+1] & 0x1);
t = (t << 1) | (bitbuf[i+2] & 0x1);
t = (t << 1) | (bitbuf[i+3] & 0x1);
t = (t << 1) | (bitbuf[i+4] & 0x1);
t = (t << 1) | (bitbuf[i+5] & 0x1);
t = (t << 1) | (bitbuf[i+6] & 0x1);
t = (t << 1) | (bitbuf[i+7] & 0x1);
*pktbuf++ = t;
}
}
void
digital_simple_correlator::update_avg(float x)
{
d_accum -= d_avgbuf[d_avbi];
d_avgbuf[d_avbi] = x;
d_accum += x;
d_avbi = (d_avbi + 1) & (AVG_PERIOD-1);
}
int
digital_simple_correlator::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];
unsigned char *out = (unsigned char*)output_items[0];
int n = 0;
int nin = ninput_items[0];
int decision;
int hamming_dist;
#ifdef DEBUG_SIMPLE_CORRELATOR
struct debug_data {
float raw_data;
float sampled;
float enter_locked;
} debug_data;
#endif
while(n < nin) {
#ifdef DEBUG_SIMPLE_CORRELATOR
debug_data.raw_data = in[n];
debug_data.sampled = 0.0;
debug_data.enter_locked = 0.0;
#endif
switch(d_state) {
case ST_LOCKED:
if(d_osi == d_center_osi) {
#ifdef DEBUG_SIMPLE_CORRELATOR
debug_data.sampled = 1.0;
#endif
decision = slice(in[n]);
d_bitbuf[d_bbi] = decision;
d_bbi++;
if(d_bbi >= d_bblen) {
// printf("got whole packet\n");
packit(d_pktbuf, d_bitbuf, d_bbi);
//printf("seqno %3d\n", d_pktbuf[0]);
memcpy(out, &d_pktbuf[GRSF_PAYLOAD_OVERHEAD], d_payload_bytesize);
enter_looking();
consume_each(n + 1);
return d_payload_bytesize;
}
}
break;
case ST_LOOKING:
case ST_UNDER_THRESHOLD:
update_avg(in[n]);
decision = slice(in[n]);
d_shift_reg[d_osi] = (d_shift_reg[d_osi] << 1) | decision;
hamming_dist = gr_count_bits64(d_shift_reg[d_osi] ^ GRSF_SYNC);
//fprintf(stderr, "%2d %d\n", hamming_dist, d_osi);
if(d_state == ST_LOOKING && hamming_dist <= THRESHOLD) {
// We're seeing a good PN code, remember location
enter_under_threshold();
}
else if(d_state == ST_UNDER_THRESHOLD && hamming_dist > THRESHOLD) {
// no longer seeing good PN code, compute center of goodness
enter_locked();
#ifdef DEBUG_SIMPLE_CORRELATOR
debug_data.enter_locked = 1.0;
#endif
}
break;
default:
assert(0);
}
#ifdef DEBUG_SIMPLE_CORRELATOR
fwrite(&debug_data, sizeof(debug_data), 1, d_debug_fp);
#endif
d_osi = add_index(d_osi, 1);
n++;
}
consume_each(n);
return 0;
}
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