119 lines
3.7 KiB
C
119 lines
3.7 KiB
C
/* (C) 2019 by Harald Welte <laforge@gnumonks.org>
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* All Rights Reserved
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*
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* SPDX-License-Identifier: GPL-2.0-or-later
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*
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* This program 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
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* by the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program 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 along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
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*/
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#define _GNU_SOURCE
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#include <string.h>
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#include <sys/types.h>
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#include <sys/stat.h>
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#include <fcntl.h>
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#include <stdint.h>
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#include <stdlib.h>
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#include <unistd.h>
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#include <errno.h>
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#include <time.h>
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#include <osmocom/core/select.h>
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#include <osmocom/core/utils.h>
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#include "prbs.h"
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/* we could generate a lookup table at start ... */
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uint8_t bits_set_in_byte(uint8_t byte)
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{
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uint8_t ret = 0;
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int i;
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for (i = 0; i < 8; i++) {
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if (byte & (1 << i))
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ret += 1;
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}
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return ret;
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}
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static uint8_t next_prbs_pc_byte(struct timeslot_state_rx *tsr)
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{
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const struct prbs_precomp *pc = &tsr->prbs_pc[tsr->sync_state.prbs_pc_num];
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uint8_t ret = pc->bytes[tsr->sync_state.prbs_pc_offset];
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tsr->sync_state.prbs_pc_offset = (tsr->sync_state.prbs_pc_offset + 1) % sizeof(pc->bytes);
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return ret;
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}
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/* compare if received buffer matches PRBS; count number of different bits */
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static unsigned int compare_buf(struct timeslot_state_rx *tsr, const uint8_t *data, unsigned int len)
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{
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unsigned int i, num_wrong_bits = 0;
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for (i = 0; i < len; i++) {
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uint8_t bt = next_prbs_pc_byte(tsr);
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if (data[i] != bt) {
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uint8_t x = data[i] ^ bt;
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num_wrong_bits += bits_set_in_byte(x);
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}
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}
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return num_wrong_bits;
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}
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/* process incoming received data; try to correlate with prbs sequence */
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void prbs_process_rx(struct timeslot_state_rx *tsr, const uint8_t *data, unsigned int len)
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{
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if (!tsr->sync_state.has_sync) {
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unsigned int pc_num;
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/* we haven't synced yet and must attempt to sync to the pattern. We will try
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* to match each pattern */
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for (pc_num = 0; pc_num < ARRAY_SIZE(tsr->prbs_pc); pc_num++) {
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const struct prbs_precomp *pc = &tsr->prbs_pc[pc_num];
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uint8_t *found;
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long int offset;
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OSMO_ASSERT(len > sizeof(pc->bytes));
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found = memmem(data, len, pc->bytes, sizeof(pc->bytes));
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if (!found)
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continue;
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offset = (found - data);
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printf("FOUND SYNC (pc_num=%u, offset=%li)\n", pc_num, offset);
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clock_gettime(CLOCK_MONOTONIC, &tsr->sync_state.ts_sync);
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tsr->sync_state.has_sync = true;
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tsr->sync_state.prbs_pc_num = pc_num;
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tsr->sync_state.prbs_pc_offset = (sizeof(pc->bytes) - offset) % sizeof(pc->bytes);
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tsr->sync_state.num_bit_err = 0;
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/* fall-through to below to compare all of the buffer */
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}
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}
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if (tsr->sync_state.has_sync) {
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unsigned int num_wrong_bits;
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/* we already have sync */
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num_wrong_bits = compare_buf(tsr, data, len);
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if (num_wrong_bits >= len*8/4) { /* more than 25% of wrong bits */
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struct timespec ts_now;
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clock_gettime(CLOCK_MONOTONIC, &ts_now);
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printf("LOST SYNC after %u of %u wrong bits in one buffer; "
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"until now, total bit errors %u in %lu seconds\n",
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num_wrong_bits, len*8, tsr->sync_state.num_bit_err,
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ts_now.tv_sec - tsr->sync_state.ts_sync.tv_sec);
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tsr->sync_state.has_sync = false;
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tsr->sync_state.num_sync_loss++;
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}
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tsr->sync_state.num_bit_err += num_wrong_bits;
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}
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}
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