gr-digital/lib/correlate_access_code_ff_ts_impl.cc

/* -*- c++ -*- */
/*
 * Copyright 2014 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 "correlate_access_code_ff_ts_impl.h"
#include <gnuradio/io_signature.h>
#include <gnuradio/math.h>
#include <volk/volk.h>
#include <boost/format.hpp>
#include <cstdio>
#include <iostream>
#include <stdexcept>

namespace gr {
namespace digital {

correlate_access_code_ff_ts::sptr correlate_access_code_ff_ts::make(
    const std::string& access_code, int threshold, const std::string& tag_name)
{
    return gnuradio::get_initial_sptr(
        new correlate_access_code_ff_ts_impl(access_code, threshold, tag_name));
}

correlate_access_code_ff_ts_impl::correlate_access_code_ff_ts_impl(
    const std::string& access_code, int threshold, const std::string& tag_name)
    : block("correlate_access_code_ff_ts",
            io_signature::make(1, 1, sizeof(float)),
            io_signature::make(1, 1, sizeof(float))),
      d_data_reg(0),
      d_mask(0),
      d_threshold(threshold),
      d_len(0)
{
    set_tag_propagation_policy(TPP_DONT);

    if (!set_access_code(access_code)) {
        GR_LOG_ERROR(d_logger, "access_code is > 64 bits");
        throw std::out_of_range("access_code is > 64 bits");
    }

    std::stringstream str;
    str << name() << unique_id();
    d_me = pmt::string_to_symbol(str.str());
    d_key = pmt::string_to_symbol(tag_name);

    d_state = STATE_SYNC_SEARCH;
    d_pkt_len = 0;
    d_pkt_count = 0;
    d_hdr_reg = 0;
    d_hdr_count = 0;
}

correlate_access_code_ff_ts_impl::~correlate_access_code_ff_ts_impl() {}

bool correlate_access_code_ff_ts_impl::set_access_code(const std::string& access_code)
{
    d_len = access_code.length(); // # of bytes in string
    if (d_len > 64)
        return false;

    // set len least significant bits to 1.
    d_mask = ((~0ULL) >> (64 - d_len));

    d_access_code = 0;
    for (unsigned i = 0; i < d_len; i++) {
        d_access_code = (d_access_code << 1) | (access_code[i] & 1);
    }

    GR_LOG_DEBUG(d_logger, boost::format("Access code: %llx") % d_access_code);
    GR_LOG_DEBUG(d_logger, boost::format("Mask: %llx") % d_mask);

    return true;
}

unsigned long long correlate_access_code_ff_ts_impl::access_code() const
{
    return d_access_code;
}

inline void correlate_access_code_ff_ts_impl::enter_search()
{
    d_state = STATE_SYNC_SEARCH;
    d_data_reg_bits = 0;
}

inline void correlate_access_code_ff_ts_impl::enter_have_sync()
{
    d_state = STATE_HAVE_SYNC;
    d_hdr_reg = 0;
    d_hdr_count = 0;
}

inline void correlate_access_code_ff_ts_impl::enter_have_header(int payload_len)
{
    d_state = STATE_HAVE_HEADER;
    d_pkt_len = 8 * payload_len;
    d_pkt_count = 0;
}

bool correlate_access_code_ff_ts_impl::header_ok()
{
    // confirm that two copies of header info are identical
    return ((d_hdr_reg >> 16) ^ (d_hdr_reg & 0xffff)) == 0;
}

int correlate_access_code_ff_ts_impl::header_payload()
{
    return (d_hdr_reg >> 16) & 0x0fff;
}

int correlate_access_code_ff_ts_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];
    float* out = (float*)output_items[0];

    uint64_t abs_out_sample_cnt = nitems_written(0);

    int nprod = 0;

    int count = 0;
    while (count < noutput_items) {
        switch (d_state) {
        case STATE_SYNC_SEARCH: // Look for the access code correlation

            while (count < noutput_items) {
                // shift in new data
                d_data_reg =
                    (d_data_reg << 1) | (gr::branchless_binary_slicer(in[count++]) & 0x1);
                if (d_data_reg_bits + 1 < d_len) {
                    d_data_reg_bits++;
                    continue;
                }
                // compute hamming distance between desired access code and current
                // data
                uint64_t wrong_bits = 0;
                uint64_t nwrong = d_threshold + 1;

                wrong_bits = (d_data_reg ^ d_access_code) & d_mask;
                volk_64u_popcnt(&nwrong, wrong_bits);

                if (nwrong <= d_threshold) {
                    enter_have_sync();
                    break;
                }
            }
            break;

        case STATE_HAVE_SYNC:
            while (count < noutput_items) { // Shift bits one at a time into header
                d_hdr_reg =
                    (d_hdr_reg << 1) | (gr::branchless_binary_slicer(in[count++]) & 0x1);
                d_hdr_count++;

                if (d_hdr_count == 32) {
                    // we have a full header, check to see if it has been received
                    // properly
                    if (header_ok()) {
                        int payload_len = header_payload();
                        enter_have_header(payload_len);
                    } else {
                        enter_search(); // bad header
                    }
                    break;
                }
            }
            break;

        case STATE_HAVE_HEADER:
            if (d_pkt_count == 0) {
                // MAKE A TAG OUT OF THIS AND UPDATE OFFSET
                add_item_tag(0,                          // stream ID
                             abs_out_sample_cnt + nprod, // sample
                             d_key,                      // length key
                             pmt::from_long(d_pkt_len),  // length data
                             d_me);                      // block src id
            }

            while (count < noutput_items) {
                if (d_pkt_count < d_pkt_len) {
                    out[nprod++] = in[count++];
                    d_pkt_count++;
                } else {
                    enter_search();
                    break;
                }
            }
            break;
        }
    }

    consume_each(noutput_items);
    return nprod;
}

} /* namespace digital */
} /* namespace gr */