95 lines
3.3 KiB
C++
95 lines
3.3 KiB
C++
/* -*- c++ -*- */
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/* @file
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* @author Piotr Krysik <ptrkrysik@gmail.com>
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* @author Vadim Yanitskiy <axilirator@gmail.com>
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* @section LICENSE
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*
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* Gr-gsm is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 3, or (at your option)
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* any later version.
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*
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* Gr-gsm is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with gr-gsm; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*
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*/
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#include <grgsm/misc_utils/fn_time.h>
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#include <grgsm/misc_utils/time_spec.h>
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#include <math.h>
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#define GSM_HYPER_FRAME (26 * 51 * 2048)
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#define GSM_SYM_RATE (13.0e6 / 48.0)
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#define GSM_TS_PERIOD (156.25 / GSM_SYM_RATE)
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#define GSM_FN_PERIOD (8 * GSM_TS_PERIOD)
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namespace gr {
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namespace gsm {
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/**
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* Computes difference between two frame numbers modulo
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* GSM_HYPER_FRAME / 2. The result is correct if difference
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* between the frame numbers is not bigger than GSM_HYPER_FRAME / 2.
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* @param fn1 first frame number
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* @param fn2 second frame number
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* @return computed difference
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*/
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static int fnmod_delta(uint32_t fn1, uint32_t fn2)
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{
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int delta, h2;
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delta = (fn1 % GSM_HYPER_FRAME) - (fn2 % GSM_HYPER_FRAME);
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h2 = GSM_HYPER_FRAME / 2;
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if (delta >= h2) {
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delta -= GSM_HYPER_FRAME;
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} else if(delta < -h2) {
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delta += GSM_HYPER_FRAME;
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}
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return delta;
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}
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static int fn_time_diff_delta(uint32_t fn, uint32_t fn_ref,
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time_spec_t time_diff_hint)
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{
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int frames_diff, fn_delta;
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frames_diff = int(round(time_diff_hint.get_real_secs() / GSM_FN_PERIOD));
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fn_delta = fnmod_delta(fn, fn_ref + frames_diff) + frames_diff;
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return fn_delta;
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}
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/**
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* Computes difference between reference frame number
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* and a second frame number.
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* @param fn_ref reference frame number modulo GSM_HYPER_FRAME
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* @param fn second frame number modulo GSM_HYPER_FRAME
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* @param time_ref precise timestamp of the first sample in the fn_ref
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* @param time_hint coarse time for fn that is used as a hint to avoid
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* ambiguities caused by modulo operation applied to
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* frame numbers
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* @return difference between fn_ref and fn
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*/
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time_format fn_time_delta_cpp(uint32_t fn_ref, time_format time_ref, uint32_t fn_x,
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time_format time_hint, uint32_t ts_num, uint32_t ts_ref)
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{
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time_spec_t time_diff_hint = time_spec_t(time_hint.first, time_hint.second) - time_spec_t(time_ref.first, time_ref.second);
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int fn_delta = fn_time_diff_delta(fn_x, fn_ref, time_diff_hint);
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time_spec_t time_x_precise = fn_delta * GSM_FN_PERIOD + time_spec_t(time_ref.first, time_ref.second) + (static_cast<int>(ts_num) - static_cast<int>(ts_ref)) * GSM_TS_PERIOD;
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return time_format(time_x_precise.get_full_secs(), time_x_precise.get_frac_secs());
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}
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} /* namespace gsm */
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} /* namespace gr */
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