lib/misc_utils/fn_time.cc

/* -*- c++ -*- */
/* @file
 * @author Piotr Krysik <ptrkrysik@gmail.com>
 * @author Vadim Yanitskiy <axilirator@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.
 * 
 */

#include <grgsm/misc_utils/fn_time.h>
#include <math.h>

#define GSM_HYPER_FRAME 26 * 51 * 2048
#define GSM_SYM_RATE 13.0e6 / 48.0

#define GSM_TS_PERIOD 156.25 / GSM_SYM_RATE
#define GSM_FN_PERIOD 8 * GSM_TS_PERIOD

namespace gr {
  namespace gsm {
  	/**
  	 * Computes difference between two frame numbers modulo
  	 * GSM_HYPER_FRAME / 2. The result is correct if difference
  	 * between the frame numbers is not bigger than GSM_HYPER_FRAME / 2.
  	 * @param  fn1 first frame number
  	 * @param  fn2 second frame number
  	 * @return     computed difference
  	 */
    static uint32_t fnmod_delta(uint32_t fn1, uint32_t fn2)
    {
      uint32_t delta, h2;

      delta = (fn1 % GSM_HYPER_FRAME) - (fn2 % GSM_HYPER_FRAME);
      h2 = GSM_HYPER_FRAME / 2;

      if (delta >= h2)
      	delta -= GSM_HYPER_FRAME;
      else
      	delta += GSM_HYPER_FRAME;

      return delta;
    }

    static int fn_time_diff_delta(uint32_t fn, uint32_t fn_ref,
      time_spec_t time_diff_hint)
    {
      int frames_diff, fn_delta;

      frames_diff = int(round(time_diff_hint.get_real_secs() / GSM_FN_PERIOD));
      fn_delta = fnmod_delta(fn, fn_ref + frames_diff) + frames_diff;

      return fn_delta;
    }

    /**
     * Computes difference between reference frame number
     * and a second frame number. 
     * @param  fn_ref    reference frame number modulo GSM_HYPER_FRAME
     * @param  fn        second frame number modulo GSM_HYPER_FRAME
     * @param  time_ref  precise timestamp of the first sample in the fn_ref
     * @param  time_hint coarse time for fn that is used as a hint to avoid
     *                   ambiguities caused by modulo operation applied to
     *                   frame numbers
     * @return           difference between fn_ref and fn
     */
    time_spec_t fn_time_delta2(uint32_t fn_ref, time_spec_t time_ref, uint32_t fn_x, 
      time_spec_t time_hint, uint32_t ts_num, uint32_t ts_ref)
    {
			time_spec_t time_diff_hint = time_hint - time_ref;
      uint32_t fn_delta = fn_time_diff_delta(fn_x,fn_ref, time_diff_hint);
      time_spec_t time_x_precise = fn_delta * GSM_FN_PERIOD
        + time_ref + (ts_num - ts_ref) * GSM_TS_PERIOD;
      
      return time_x_precise;
    }
/*
    def fn_time_delta(fn_ref, time_ref, fn_x, time_hint=None, ts_num=0, ts_ref=0):
      if time_hint is None:
          time_hint = time_ref
          
      time_diff_hint = time_hint-time_ref
      fn_delta = fn_time_diff_delta(fn_x,fn_ref, time_diff_hint)
      time_x_precise = fn_delta*__frame_period+time_ref+(ts_num-ts_ref)*__ts_period
      
      return fn_delta, time_x_precise
*/
  } /* namespace gsm */
} /* namespace gr */