147 lines
4.1 KiB
C
147 lines
4.1 KiB
C
/* GMR-1 FACCH9 channel coding */
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/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.11 */
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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 facch9
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* @{
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*/
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/*! \file l1/facch9.c
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* \brief Osmocom GMR-1 FACCH9 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_facch9;
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static void __attribute__ ((constructor))
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gmr1_facch9_init(void)
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{
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/* Init convolutional coder */
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memcpy(&gmr1_conv_facch9, &gmr1_conv_12, sizeof(struct osmo_conv_code));
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gmr1_conv_facch9.len = 316;
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}
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/*! \brief Stateless GMR-1 FACCH9 channel coder
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* \param[out] bits_e 662 encoded bits of one NT9 burst
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* \param[in] l2 L2 packet data (38 bytes, last nibble unused)
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* \param[in] bits_sacch 10 saach bits to be multiplexed
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* \param[in] bits_status 4 status bits to be multiplexed
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* \param[in] ciph 658 bits of cipher stream (can be NULL)
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*/
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void
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gmr1_facch9_encode(ubit_t *bits_e, const uint8_t *l2,
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const ubit_t *bits_sacch, const ubit_t *bits_status,
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const ubit_t *ciph)
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{
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ubit_t bits_u[316];
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ubit_t bits_c[640];
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ubit_t bits_epp_x[648];
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ubit_t bits_my[658];
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int i;
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osmo_pbit2ubit_ext(bits_u, 0, l2, 0, 300, 1);
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osmo_crc16gen_set_bits(&gmr1_crc16, bits_u, 300, bits_u+300);
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osmo_conv_encode(&gmr1_conv_facch9, bits_u, bits_c);
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memset(bits_epp_x, 0, 4);
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memset(bits_epp_x+644, 0, 4);
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gmr1_interleave_intra(bits_epp_x+4, bits_c, 80);
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gmr1_scramble_ubit(bits_epp_x, bits_epp_x, 648);
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memcpy(bits_my, bits_epp_x, 52);
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memcpy(bits_my+52, bits_sacch, 10);
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memcpy(bits_my+62, bits_epp_x+52, 596);
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if (ciph) {
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for (i=0; i<658; i++)
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bits_my[i] ^= ciph[i];
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}
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memcpy(bits_e, bits_my, 52);
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memcpy(bits_e+52, bits_status, 4);
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memcpy(bits_e+56, bits_my+52, 606);
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}
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/*! \brief Stateless GMR-1 FACCH9 channel decoder
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* \param[out] l2 L2 packet data (38 bytes, last nibble unused)
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* \param[out] bits_sacch 10 saach bits demultiplexed
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* \param[out] bits_status 4 status bits demultiplexed
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* \param[in] bits_e 662 encoded bits of one NT9 burst
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* \param[in] ciph 658 bits of cipher stream (can be NULL)
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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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int
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gmr1_facch9_decode(uint8_t *l2, sbit_t *bits_sacch, sbit_t *bits_status,
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const sbit_t *bits_e, const ubit_t *ciph, int *conv_rv)
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{
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sbit_t bits_my[658];
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sbit_t bits_epp_x[648];
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sbit_t bits_c[640];
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ubit_t bits_u[316];
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int i, rv;
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memcpy(bits_my, bits_e, 52);
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memcpy(bits_status, bits_e+52, 4);
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memcpy(bits_my+52, bits_e+56, 606);
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if (ciph) {
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for (i=0; i<658; i++)
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if (ciph[i])
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bits_my[i] *= -1;
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}
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memcpy(bits_epp_x, bits_my, 52);
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memcpy(bits_sacch, bits_my+52, 10);
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memcpy(bits_epp_x+52, bits_my+62, 596);
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gmr1_scramble_sbit(bits_epp_x, bits_epp_x, 648);
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gmr1_deinterleave_intra(bits_c, bits_epp_x+4, 80);
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rv = osmo_conv_decode(&gmr1_conv_facch9, 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, 300, bits_u+300);
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l2[37] = 0; /* upper nibble won't be written */
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osmo_ubit2pbit_ext(l2, 0, bits_u, 0, 300, 1);
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return rv;
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}
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/*! @} */
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