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/* GMR-1 FACCH3 channel coding */
/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.9 */
/* (C) 2011-2016 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 facch3
* @{
*/
/*! \file l1/facch3.c
* \brief Osmocom GMR-1 FACCH3 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_facch3;
static void __attribute__ ((constructor))
gmr1_facch3_init(void)
{
/* Init convolutional coder */
memcpy(&gmr1_conv_facch3, &gmr1_conv_k5_14, sizeof(struct osmo_conv_code));
gmr1_conv_facch3.len = 92;
}
/*! \brief Stateless GMR-1 FACCH3 channel coder
* \param[out] bits_e 4*104 encoded bits of 4 bursts
* \param[in] l2 L2 packet data
* \param[in] bits_s 4*8 status bits to be multiplexed
* \param[in] ciph 4*96 bits of cipher stream (can be NULL)
*
* L2 data is 10 byte long.
* bits_s is 32 bits, 8 bits for each of the 4 burts, organized as 4 s_n
* followed by 4 s_p, as shown in section 7.3.2.2.
* bits_e is a 432 hard bit array to be mapped on 4 bursts.
* ciph is the A5 cipher stream to use, 96 bits for each of the 4 burts.
*/
void
gmr1_facch3_encode(ubit_t *bits_e, const uint8_t *l2,
const ubit_t *bits_s, const ubit_t *ciph)
{
ubit_t bits_u[92];
ubit_t bits_c[384];
ubit_t bits_cp[96*4];
ubit_t bits_ep[96*4];
ubit_t bits_xmy[96*4];
int i, j;
osmo_pbit2ubit_ext(bits_u, 0, l2, 0, 76, 1);
osmo_crc16gen_set_bits(&gmr1_crc16, bits_u, 76, bits_u+76);
osmo_conv_encode(&gmr1_conv_facch3, bits_u, bits_c);
for (i=0; i<384; i++)
bits_cp[(i&3)*96 + (i>>2)] = bits_c[i];
for (i=0; i<4; i++)
{
ubit_t *b_bits_cp = bits_cp + 96*i;
ubit_t *b_bits_ep = bits_ep + 96*i;
ubit_t *b_bits_xmy = bits_xmy + 96*i;
ubit_t *b_bits_e = bits_e + 104*i;
const ubit_t *b_bits_s = bits_s + 8*i;
const ubit_t *b_ciph = ciph + 96*i;
gmr1_interleave_intra(b_bits_ep, b_bits_cp, 12);
gmr1_scramble_ubit(b_bits_xmy, b_bits_ep, 96);
if (ciph) {
for (j=0; j<96; j++)
b_bits_xmy[j] ^= b_ciph[j];
}
memcpy(b_bits_e , b_bits_xmy, 22);
memcpy(b_bits_e+22, b_bits_s, 8);
memcpy(b_bits_e+30, b_bits_xmy+22, 74);
}
}
/*! \brief Stateless GMR-1 FACCH3 channel decoder
* \param[out] l2 L2 packet data
* \param[out] bits_s 4*8 status bits de-multiplexed
* \param[in] bits_e 4*104 encoded bits of 4 bursts
* \param[in] ciph 4*96 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.
*
* L2 data is 10 byte long.
* bits_s is 32 bits, 8 bits for each of the 4 burts, organized as 4 s_n
* followed by 4 s_p, as shown in section 7.3.2.2.
* bits_e is a 424 soft bits array unmapped from 4 bursts.
* ciph is the A5 cipher stream to use, 96 bits for each of the 4 burts.
*/
int
gmr1_facch3_decode(uint8_t *l2, ubit_t *bits_s,
const sbit_t *bits_e, const ubit_t *ciph, int *conv_rv)
{
sbit_t bits_xmy[96*4];
sbit_t bits_ep[96*4];
sbit_t bits_cp[96*4];
sbit_t bits_c[384];
ubit_t bits_u[92];
int rv, i, j;
for (i=0; i<4; i++)
{
const sbit_t *b_bits_e = bits_e + 104*i;
ubit_t *b_bits_s = bits_s + 8*i;
sbit_t *b_bits_xmy = bits_xmy + 96*i;
sbit_t *b_bits_ep = bits_ep + 96*i;
sbit_t *b_bits_cp = bits_cp + 96*i;
const ubit_t *b_ciph = ciph + 96*i;
for (j=0; j<8; j++)
b_bits_s[j] = b_bits_e[22+j] < 0;
memcpy(b_bits_xmy, b_bits_e, 22);
memcpy(b_bits_xmy+22, b_bits_e+30, 74);
if (ciph) {
for (j=0; j<96; j++)
if (b_ciph[j])
b_bits_xmy[j] *= -1;
}
gmr1_scramble_sbit(b_bits_ep, b_bits_xmy, 96);
gmr1_deinterleave_intra(b_bits_cp, b_bits_ep, 12);
};
for (i=0; i<384; i++)
bits_c[i] = bits_cp[(i&3)*96 + (i>>2)];
rv = osmo_conv_decode(&gmr1_conv_facch3, bits_c, bits_u);
if (conv_rv)
*conv_rv = rv;
rv = osmo_crc16gen_check_bits(&gmr1_crc16, bits_u, 76, bits_u+76);
l2[9] = 0; /* upper nibble won't be written */
osmo_ubit2pbit_ext(l2, 0, bits_u, 0, 76, 1);
return rv;
}
/*! @} */
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