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Diffstat (limited to 'lib/misc_utils/fn_time.cc')
| -rw-r--r-- | lib/misc_utils/fn_time.cc | 94 |
1 files changed, 94 insertions, 0 deletions
diff --git a/lib/misc_utils/fn_time.cc b/lib/misc_utils/fn_time.cc new file mode 100644 index 0000000..2773f33 --- /dev/null +++ b/lib/misc_utils/fn_time.cc @@ -0,0 +1,94 @@ +/* -*- 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 */ + |