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/* -*- 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 <grgsm/misc_utils/time_spec.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 int fnmod_delta(uint32_t fn1, uint32_t fn2)
{
int delta, h2;
delta = (fn1 % GSM_HYPER_FRAME) - (fn2 % GSM_HYPER_FRAME);
h2 = GSM_HYPER_FRAME / 2;
if (delta >= h2) {
delta -= GSM_HYPER_FRAME;
} else if(delta < -h2) {
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_format fn_time_delta_cpp(uint32_t fn_ref, time_format time_ref, uint32_t fn_x,
time_format time_hint, uint32_t ts_num, uint32_t ts_ref)
{
time_spec_t time_diff_hint = time_spec_t(time_hint.first, time_hint.second) - time_spec_t(time_ref.first, time_ref.second);
int 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_spec_t(time_ref.first, time_ref.second) + (static_cast<int>(ts_num) - static_cast<int>(ts_ref)) * GSM_TS_PERIOD;
return time_format(time_x_precise.get_full_secs(), time_x_precise.get_frac_secs());
}
} /* namespace gsm */
} /* namespace gr */
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