/* GMR-1 FACCH3 channel coding */ /* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.9 */ /* (C) 2011-2019 by Sylvain Munaut * 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 . */ /*! \addtogroup facch3 * @{ */ /*! \file l1/facch3.c * \brief Osmocom GMR-1 FACCH3 channel coding implementation */ #include #include #include #include #include #include #include #include #include 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; } /*! @} */