diff options
author | Sylvain Munaut <tnt@246tNt.com> | 2011-11-19 19:13:31 +0100 |
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committer | Sylvain Munaut <tnt@246tNt.com> | 2011-12-14 23:02:53 +0100 |
commit | 77037d37bc78ea166d9e5fdea954cf1056f9d4b9 (patch) | |
tree | 4e3f66df6ebe05369433583af6a02e9117825600 /src/l1 | |
parent | 98db75d85ed82979a9f1a681693acf3a8df056c0 (diff) |
l1/facch3: Add support for FACCH3 channel coding
Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Diffstat (limited to 'src/l1')
-rw-r--r-- | src/l1/Makefile.am | 2 | ||||
-rw-r--r-- | src/l1/facch3.c | 168 |
2 files changed, 169 insertions, 1 deletions
diff --git a/src/l1/Makefile.am b/src/l1/Makefile.am index 4857242..05e068c 100644 --- a/src/l1/Makefile.am +++ b/src/l1/Makefile.am @@ -6,4 +6,4 @@ noinst_LIBRARIES = libgmr1-l1.a libgmr1_l1_a_SOURCES = \ conv.c crc.c interleave.c punct.c scramb.c \ - bcch.c ccch.c + bcch.c ccch.c facch3.c diff --git a/src/l1/facch3.c b/src/l1/facch3.c new file mode 100644 index 0000000..d3c847f --- /dev/null +++ b/src/l1/facch3.c @@ -0,0 +1,168 @@ +/* GMR-1 FACCH3 channel coding */ +/* See GMR-1 05.003 (ETSI TS 101 376-5-3 V1.2.1) - Section 6.9 */ + +/* (C) 2011 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/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_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; +} + +/*! }@ */ |