106 lines
2.8 KiB
C
106 lines
2.8 KiB
C
/* GMR-1 BCCH channel coding */
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/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.1 */
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/* (C) 2011-2019 by Sylvain Munaut <tnt@246tNt.com>
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* All Rights Reserved
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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 Affero General Public License as published by
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* the Free Software Foundation; either version 3 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 Affero General Public License for more details.
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*
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* You should have received a copy of the GNU Affero General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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/*! \addtogroup bcch
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* @{
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*/
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/*! \file l1/bcch.c
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* \brief Osmocom GMR-1 BCCH channel coding implementation
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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/bits.h>
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#include <osmocom/core/conv.h>
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#include <osmocom/core/crc16gen.h>
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#include <osmocom/gmr1/l1/conv.h>
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#include <osmocom/gmr1/l1/crc.h>
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#include <osmocom/gmr1/l1/interleave.h>
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#include <osmocom/gmr1/l1/scramb.h>
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static struct osmo_conv_code gmr1_conv_bcch;
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static void __attribute__ ((constructor))
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gmr1_bcch_init(void)
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{
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/* Init convolutional coder */
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memcpy(&gmr1_conv_bcch, &gmr1_conv_12, sizeof(struct osmo_conv_code));
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gmr1_conv_bcch.len = 208;
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}
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/*! \brief Stateless GMR-1 BCCH channel coder
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* \param[out] bits_e Data bits of a burst
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* \param[in] l2 L2 packet data
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*
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* L2 data is 24 byte long, and bits_e is a 424 hard bit array to be
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* mapped on a burst.
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*/
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void
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gmr1_bcch_encode(ubit_t *bits_e, const uint8_t *l2)
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{
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ubit_t bits_u[208];
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ubit_t bits_c[424];
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ubit_t bits_ep[424];
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osmo_pbit2ubit_ext(bits_u, 0, l2, 0, 192, 1);
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osmo_crc16gen_set_bits(&gmr1_crc16, bits_u, 192, bits_u+192);
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osmo_conv_encode(&gmr1_conv_bcch, bits_u, bits_c);
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gmr1_interleave_intra(bits_ep, bits_c, 53);
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gmr1_scramble_ubit(bits_e, bits_ep, 424);
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}
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/*! \brief Stateless GMR-1 BCCH channel decoder
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* \param[out] l2 L2 packet data
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* \param[in] bits_e Data bits of a burst
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* \param[out] conv_rv Return of the convolutional decode (can be NULL)
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* \return 0 if CRC check pass, any other value for fail.
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*
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* L2 data is 24 byte long, and bits_e is a 424 soft bit array
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* unmapped from a burst.
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*/
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int
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gmr1_bcch_decode(uint8_t *l2, const sbit_t *bits_e, int *conv_rv)
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{
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sbit_t bits_ep[424];
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sbit_t bits_c[424];
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ubit_t bits_u[208];
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int rv;
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gmr1_scramble_sbit(bits_ep, bits_e, 424);
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gmr1_deinterleave_intra(bits_c, bits_ep, 53);
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rv = osmo_conv_decode(&gmr1_conv_bcch, bits_c, bits_u);
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if (conv_rv)
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*conv_rv = rv;
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rv = osmo_crc16gen_check_bits(&gmr1_crc16, bits_u, 192, bits_u+192);
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osmo_ubit2pbit_ext(l2, 0, bits_u, 0, 192, 1);
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return rv;
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}
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/*! @} */
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