lib/receiver/clock_offset_control_impl.cc

/* -*- c++ -*- */
/*
 * @file
 * @author Piotr Krysik <ptrkrysik@gmail.com>
 * @section LICENSE
 *
 * Gr-gsm 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.
 *
 * Gr-gsm 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 gr-gsm; 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 <sch.h>
#include "clock_offset_control_impl.h"

namespace gr
{
namespace gsm
{
clock_offset_control::sptr
clock_offset_control::make(float fc)
{
    return gnuradio::get_initial_sptr
           (new clock_offset_control_impl(fc));
}


/*
 * The private constructor
 */
clock_offset_control_impl::clock_offset_control_impl(float fc)
    : gr::block("clock_offset_control",
                gr::io_signature::make(0, 0, 0),
                gr::io_signature::make(0, 0, 0))

{
    message_port_register_in(pmt::mp("measurements"));
    set_msg_handler(pmt::mp("measurements"), boost::bind(&clock_offset_control_impl::process_measurement, this, _1));    
    message_port_register_out(pmt::mp("ppm"));
    
    set_fc(fc);
    d_alfa = 0.3;
    d_ppm_estimate = -1e6;
    d_last_ppm_estimate = -1e6;    
    d_first_measurement = true;
    d_counter = 0;
    d_last_state = "";
    d_current_time = 0;
    d_last_fcch_time = 0;
    d_first_time = true;
}

/*
 * Our virtual destructor.
 */
clock_offset_control_impl::~clock_offset_control_impl()
{
}

void clock_offset_control_impl::set_fc(float fc)
{
    d_fc = fc;
}

void clock_offset_control_impl::process_measurement(pmt::pmt_t msg)
{
    if(pmt::is_tuple(msg))
    {
        std::string key = pmt::symbol_to_string(pmt::tuple_ref(msg,0));
        if(key == "current_time")
        {
            d_current_time = pmt::to_double(pmt::tuple_ref(msg,1));
            if(d_first_time==true)
            {
                d_last_fcch_time = d_current_time;
                d_first_time = false;
            }
            else
            if((d_current_time - d_last_fcch_time) > 0.5 && d_last_state == "fcch_search")
            {
                timed_reset();
            }
        }
        else 
        if(key == "freq_offset")
        {
            float freq_offset = pmt::to_double(pmt::tuple_ref(msg,1));
            float ppm = -freq_offset/d_fc*1.0e6;
            std::string state = pmt::symbol_to_string(pmt::tuple_ref(msg,2));
            d_last_state = state;
            if(abs(ppm) > 100) //safeguard against flawed measurements
            {
                ppm=0;
                reset();
            }

            if(state == "fcch_search")
            {
                pmt::pmt_t msg_ppm = pmt::from_double(ppm);
                message_port_pub(pmt::intern("ppm"), msg_ppm);
                d_last_fcch_time = d_current_time;
            } 
            else 
            if (state == "synchronized")
            {
                d_last_fcch_time = d_current_time;
                if(d_first_measurement)
                {
                    d_ppm_estimate = ppm;
                    d_first_measurement = false; 
                }
                else
                {
                    d_ppm_estimate = (1-d_alfa)*d_ppm_estimate+d_alfa*ppm;
                }
                
                if(d_counter == 5)
                {
                    d_counter = 0;
                    if(abs(d_last_ppm_estimate-d_ppm_estimate) > 0.1)
                    {
                        pmt::pmt_t msg_ppm = pmt::from_double(ppm);
                        message_port_pub(pmt::intern("ppm"), msg_ppm);
                        d_last_ppm_estimate = d_ppm_estimate;
                    }
                }
                else
                {
                    d_counter=d_counter+1;
                }
            } 
            else
            if(state == "sync_loss")
            {
                reset();
                pmt::pmt_t msg_ppm = pmt::from_double(0.0);
                message_port_pub(pmt::intern("ppm"), msg_ppm);
            }            
        }
    }
}

void clock_offset_control_impl::timed_reset()
{
    reset();
    pmt::pmt_t msg_ppm = pmt::from_double(0.0);
    message_port_pub(pmt::intern("ppm"), msg_ppm);
}


void clock_offset_control_impl::reset()
{
    d_ppm_estimate = -1e6;
    d_counter = 0;
    d_first_measurement = true;
}

} /* namespace gsm */
} /* namespace gr */