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/* GMR-1 FACCH9 channel coding */
/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.11 */
/* (C) 2012 by Sylvain Munaut <tnt@246tNt.com>
* All Rights Reserved
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program 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 Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/*! \addtogroup facch9
* @{
*/
/*! \file l1/facch9.c
* \brief Osmocom GMR-1 FACCH9 channel coding implementation
*/
#include <stdint.h>
#include <string.h>
#include <osmocom/core/bits.h>
#include <osmocom/core/conv.h>
#include <osmocom/core/crc16gen.h>
#include <osmocom/gmr1/l1/conv.h>
#include <osmocom/gmr1/l1/crc.h>
#include <osmocom/gmr1/l1/interleave.h>
#include <osmocom/gmr1/l1/scramb.h>
static struct osmo_conv_code gmr1_conv_facch9;
static void __attribute__ ((constructor))
gmr1_facch9_init(void)
{
/* Init convolutional coder */
memcpy(&gmr1_conv_facch9, &gmr1_conv_12, sizeof(struct osmo_conv_code));
gmr1_conv_facch9.len = 316;
}
/*! \brief Stateless GMR-1 FACCH9 channel coder
* \param[out] bits_e 662 encoded bits of one NT9 burst
* \param[in] l2 L2 packet data (38 bytes, last nibble unused)
* \param[in] bits_sacch 10 saach bits to be multiplexed
* \param[in] bits_status 4 status bits to be multiplexed
* \param[in] ciph 658 bits of cipher stream (can be NULL)
*/
void
gmr1_facch9_encode(ubit_t *bits_e, const uint8_t *l2,
const ubit_t *bits_sacch, const ubit_t *bits_status,
const ubit_t *ciph)
{
ubit_t bits_u[316];
ubit_t bits_c[640];
ubit_t bits_epp_x[648];
ubit_t bits_my[658];
int i;
osmo_pbit2ubit_ext(bits_u, 0, l2, 0, 300, 1);
osmo_crc16gen_set_bits(&gmr1_crc16, bits_u, 300, bits_u+300);
osmo_conv_encode(&gmr1_conv_facch9, bits_u, bits_c);
memset(bits_epp_x, 0, 4);
memset(bits_epp_x+644, 0, 4);
gmr1_interleave_intra(bits_epp_x+4, bits_c, 80);
gmr1_scramble_ubit(bits_epp_x, bits_epp_x, 648);
memcpy(bits_my, bits_epp_x, 52);
memcpy(bits_my+52, bits_sacch, 10);
memcpy(bits_my+62, bits_epp_x+52, 596);
if (ciph) {
for (i=0; i<658; i++)
bits_my[i] ^= ciph[i];
}
memcpy(bits_e, bits_my, 52);
memcpy(bits_e+52, bits_status, 4);
memcpy(bits_e+56, bits_my+52, 606);
}
/*! \brief Stateless GMR-1 FACCH9 channel decoder
* \param[out] l2 L2 packet data (38 bytes, last nibble unused)
* \param[out] bits_sacch 10 saach bits demultiplexed
* \param[out] bits_status 4 status bits demultiplexed
* \param[in] bits_e 662 encoded bits of one NT9 burst
* \param[in] ciph 658 bits of cipher stream (can be NULL)
* \param[out] conv_rv Return of the convolutional decode (can be NULL)
* \return 0 if CRC check pass, any other value for fail.
*/
int
gmr1_facch9_decode(uint8_t *l2, sbit_t *bits_sacch, sbit_t *bits_status,
const sbit_t *bits_e, const ubit_t *ciph, int *conv_rv)
{
sbit_t bits_my[658];
sbit_t bits_epp_x[648];
sbit_t bits_c[640];
ubit_t bits_u[316];
int i, rv;
memcpy(bits_my, bits_e, 52);
memcpy(bits_status, bits_e+52, 4);
memcpy(bits_my+52, bits_e+56, 606);
if (ciph) {
for (i=0; i<658; i++)
if (ciph[i])
bits_my[i] *= -1;
}
memcpy(bits_epp_x, bits_my, 52);
memcpy(bits_sacch, bits_my+52, 10);
memcpy(bits_epp_x+52, bits_my+62, 596);
gmr1_scramble_sbit(bits_epp_x, bits_epp_x, 648);
gmr1_deinterleave_intra(bits_c, bits_epp_x+4, 80);
rv = osmo_conv_decode(&gmr1_conv_facch9, bits_c, bits_u);
if (conv_rv)
*conv_rv = rv;
rv = osmo_crc16gen_check_bits(&gmr1_crc16, bits_u, 300, bits_u+300);
l2[37] = 0; /* upper nibble won't be written */
osmo_ubit2pbit_ext(l2, 0, bits_u, 0, 300, 1);
return rv;
}
/*! @} */
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