184 lines
3.7 KiB
C
184 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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#include <stdint.h>
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#include <string.h>
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#include <osmocom/core/utils.h>
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#include <osmocom/core/prbs.h>
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#include "prbs.h"
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/* according to https://users.ece.cmu.edu/~koopman/lfsr/index.html all below
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* coefficients should render maximal length LFSRs of 11bit (2048) length */
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static const uint32_t prbs11_coeff[] = {
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0x402,
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0x40B,
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0x415,
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0x416,
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0x423,
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0x431,
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0x432,
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0x438,
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0x43D,
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0x446,
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0x44A,
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0x44F,
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0x454,
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0x458,
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0x467,
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0x468,
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0x470,
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0x473,
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0x475,
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0x47A,
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0x486,
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0x489,
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0x492,
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0x494,
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0x49D,
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0x49E,
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0x4A2,
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0x4A4,
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0x4A8,
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0x4AD,
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0x4B9,
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0x4BA,
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0x4BF,
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0x4C1,
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0x4C7,
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0x4D5,
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0x4D6,
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0x4DC,
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0x4E3,
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0x4EC,
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0x4F2,
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0x4FB,
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0x500,
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0x503,
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0x509,
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0x50A,
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0x514,
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0x524,
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0x530,
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0x536,
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0x53C,
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0x53F,
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0x542,
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0x548,
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0x54E,
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0x553,
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0x555,
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0x559,
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0x55A,
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0x56A,
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0x56F,
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0x574,
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0x577,
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0x578,
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0x57D,
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0x581,
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0x584,
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0x588,
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0x599,
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0x59F,
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0x5A0,
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0x5A5,
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0x5AC,
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0x5AF,
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0x5B2,
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0x5B7,
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0x5BE,
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0x5C3,
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0x5C5,
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0x5C9,
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0x5CA,
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0x5D7,
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0x5DB,
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0x5DE,
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0x5E4,
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0x5ED,
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0x5EE,
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0x5F3,
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0x5F6,
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0x605,
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0x606,
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0x60C,
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0x60F,
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0x62B,
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0x630,
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0x635,
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0x639,
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0x642,
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0x644,
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0x64B
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};
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/* build the PRBS description for a given timeslot number */
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void prbs_for_ts_nr(struct osmo_prbs *prbs, uint8_t ts_nr)
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{
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OSMO_ASSERT(ts_nr < ARRAY_SIZE(prbs11_coeff));
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prbs->name = "custom";
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prbs->len = 11;
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prbs->coeff = prbs11_coeff[ts_nr];
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}
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/* compute one full sequence of the given PRBS */
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void prbs_precomp(struct prbs_precomp *out, const struct osmo_prbs *prbs)
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{
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struct osmo_prbs_state prbs_s;
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int i;
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osmo_prbs_state_init(&prbs_s, prbs);
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for (i = 0; i < sizeof(out->bytes); i++) {
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ubit_t ubit[8];
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osmo_prbs_get_ubits(ubit, sizeof(ubit), &prbs_s);
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osmo_ubit2pbit(&out->bytes[i], ubit, sizeof(ubit));
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}
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}
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void ts_init_prbs_tx(struct timeslot_state *ts, unsigned int prbs_offs_tx)
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{
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unsigned int prbs_nr = prbs_offs_tx + ts->ofd.priv_nr;
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/* initialize the transmit-side PRNG for this slot */
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printf("Selecting PRBS11 #%02u for Tx of TS%02u\n", prbs_nr, ts->ofd.priv_nr);
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prbs_for_ts_nr(&ts->tx.prbs, prbs_nr);
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prbs_precomp(&ts->tx.prbs_pc, &ts->tx.prbs);
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}
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void ts_init_prbs_rx(struct timeslot_state *ts, unsigned int prbs_offs_rx)
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{
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unsigned int prbs_nr = prbs_offs_rx + ts->ofd.priv_nr;
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/* initialize the receive-side PRNG for this slot */
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ubit_t ubit[PRBS_LEN*2];
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printf("Selecting PRBS11 #%02u for Rx of TS%02u\n", prbs_nr, ts->ofd.priv_nr);
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prbs_for_ts_nr(&ts->rx.prbs, prbs_nr);
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prbs_precomp(&ts->rx.prbs_pc[0], &ts->rx.prbs);
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osmo_pbit2ubit(ubit, ts->rx.prbs_pc[0].bytes, PRBS_LEN);
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/* copy buffer twice back-to-back */
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memcpy(ubit+PRBS_LEN, ubit, PRBS_LEN);
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/* pre-compute bit-shifted versions */
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for (int i = 1; i < ARRAY_SIZE(ts->rx.prbs_pc); i++) {
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osmo_ubit2pbit_ext(ts->rx.prbs_pc[i].bytes, 0, ubit, i, PRBS_LEN, 0);
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//printf("%d: %s\n", i, osmo_hexdump_nospc(ts->prbs_pc[i].bytes, sizeof(ts->prbs_pc[i].bytes)));
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}
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}
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