| /* -*- c++ -*- */ |
| /* |
| * @file |
| * @author (C) 2014 by Piotr Krysik <ptrkrysik@gmail.com> |
| * @section LICENSE |
| * |
| * Gr-gsm is free software; you can redistribute it and/or modify |
| * it under the terms of the GNU General Public License as published by |
| * the Free Software Foundation; either version 3, or (at your option) |
| * any later version. |
| * |
| * Gr-gsm 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 General Public License for more details. |
| * |
| * You should have received a copy of the GNU General Public License |
| * along with gr-gsm; see the file COPYING. If not, write to |
| * the Free Software Foundation, Inc., 51 Franklin Street, |
| * Boston, MA 02110-1301, USA. |
| */ |
| |
| #include <string.h> |
| #include "gsm_constants.h" |
| |
| #include "osmocom/coding/gsm0503_coding.h" |
| #include <osmocom/core/utils.h> |
| |
| static int ubits2sbits(ubit_t *ubits, sbit_t *sbits, int count) |
| { |
| int i; |
| |
| for (i = 0; i < count; i++) { |
| if (*ubits == 0x23) { |
| ubits++; |
| sbits++; |
| continue; |
| } |
| if ((*ubits++) & 1) |
| *sbits++ = -127; |
| else |
| *sbits++ = 127; |
| } |
| |
| return count; |
| } |
| |
| int decode_sch(const unsigned char *buf, int * t1_o, int * t2_o, int * t3_o, int * ncc_o, int * bcc_o) |
| { |
| |
| int t1, t2, t3p, t3, ncc, bcc; |
| |
| uint8_t result[4]; |
| ubit_t bursts_u[SCH_DATA_LEN*2]; |
| sbit_t bursts_s[SCH_DATA_LEN*2]; |
| |
| // extract encoded data from synchronization burst |
| /* buf, 39 bit */ |
| /* buf + 39 + 64 = 103, 39 */ |
| memcpy(bursts_u, buf, SCH_DATA_LEN); |
| memcpy(bursts_u + SCH_DATA_LEN, buf + SCH_DATA_LEN + N_SYNC_BITS, SCH_DATA_LEN); |
| |
| ubits2sbits(bursts_u, bursts_s, SCH_DATA_LEN*2); |
| if(gsm0503_sch_decode(result, bursts_s)==-1){ |
| return 1; |
| } |
| |
| // Synchronization channel information, 44.018 page 171. (V7.2.0) |
| uint8_t decoded_data[25]; |
| osmo_pbit2ubit_ext(decoded_data, 0, result, 0, 25, 1); |
| ncc = |
| (decoded_data[ 7] << 2) | |
| (decoded_data[ 6] << 1) | |
| (decoded_data[ 5] << 0); |
| bcc = |
| (decoded_data[ 4] << 2) | |
| (decoded_data[ 3] << 1) | |
| (decoded_data[ 2] << 0); |
| t1 = |
| (decoded_data[ 1] << 10) | |
| (decoded_data[ 0] << 9) | |
| (decoded_data[15] << 8) | |
| (decoded_data[14] << 7) | |
| (decoded_data[13] << 6) | |
| (decoded_data[12] << 5) | |
| (decoded_data[11] << 4) | |
| (decoded_data[10] << 3) | |
| (decoded_data[ 9] << 2) | |
| (decoded_data[ 8] << 1) | |
| (decoded_data[23] << 0); |
| t2 = |
| (decoded_data[22] << 4) | |
| (decoded_data[21] << 3) | |
| (decoded_data[20] << 2) | |
| (decoded_data[19] << 1) | |
| (decoded_data[18] << 0); |
| t3p = |
| (decoded_data[17] << 2) | |
| (decoded_data[16] << 1) | |
| (decoded_data[24] << 0); |
| |
| t3 = 10 * t3p + 1; |
| |
| // modulo arithmetic t3 - t2 mod 26 |
| // tt = ((t3 + 26) - t2) % 26; |
| |
| // fn = (51 * 26 * t1) + (51 * tt) + t3; |
| |
| /* |
| * BSIC: Base Station Identification Code |
| * BCC: Base station Color Code |
| * NCC: Network Color Code |
| * |
| * FN: Frame Number |
| */ |
| |
| // printf("bsic: %x (bcc: %u; ncc: %u)\tFN: %u\n", bsic, bsic & 7, |
| // (bsic >> 3) & 7, fn); |
| |
| // if (fn_o) |
| // *fn_o = fn; |
| // if (bsic_o) |
| if (t1_o && t2_o && t3_o && ncc_o && bcc_o) { |
| *t1_o = t1; |
| *t2_o = t2; |
| *t3_o = t3; |
| *bcc_o = bcc; |
| *ncc_o = ncc; |
| } |
| |
| return 0; |
| } |