157 lines
3.2 KiB
C
157 lines
3.2 KiB
C
#include <complex.h>
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#include <stdio.h>
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#include <math.h>
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#include <string.h>
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#include <osmocom/core/bits.h>
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#include <osmocom/core/conv.h>
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#include <osmocom/core/utils.h>
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#include <osmocom/core/crcgen.h>
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#include "sch.h"
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/* GSM 04.08, 9.1.30 Synchronization channel information */
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struct sch_packed_info {
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ubit_t t1_hi[2];
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ubit_t bsic[6];
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ubit_t t1_md[8];
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ubit_t t3p_hi[2];
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ubit_t t2[5];
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ubit_t t1_lo[1];
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ubit_t t3p_lo[1];
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} __attribute__((packed));
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struct sch_burst {
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sbit_t tail0[3];
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sbit_t data0[39];
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sbit_t etsc[64];
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sbit_t data1[39];
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sbit_t tail1[3];
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sbit_t guard[8];
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} __attribute__((packed));
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static const uint8_t sch_next_output[][2] = {
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{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
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{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
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{ 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
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{ 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
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};
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static const uint8_t sch_next_state[][2] = {
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{ 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
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{ 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
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{ 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
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{ 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
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};
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static const struct osmo_conv_code gsm_conv_sch = {
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.N = 2,
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.K = 5,
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.len = GSM_SCH_UNCODED_LEN,
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.next_output = sch_next_output,
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.next_state = sch_next_state,
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};
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const struct osmo_crc16gen_code gsm0503_sch_crc10 = {
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.bits = 10,
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.poly = 0x175,
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.init = 0x000,
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.remainder = 0x3ff,
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};
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#define GSM_MAX_BURST_LEN 157
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#define GSM_SYM_RATE (1625e3 / 6)
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int float_to_sbit(const float *in, sbit_t *out, float scale, int len)
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{
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int i;
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for (i = 0; i < len; i++) {
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out[i] = (in[i] - 0.5f) * scale;
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}
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return 0;
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}
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/* Check if FN contains a SCH burst */
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int gsm_sch_check_fn(int fn)
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{
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int fn51 = fn % 51;
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switch (fn51) {
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case 1:
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case 11:
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case 21:
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case 31:
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case 41:
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return 1;
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}
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return 0;
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}
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/* SCH (T1, T2, T3p) to full FN value */
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int gsm_sch_to_fn(struct sch_info *sch)
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{
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int t1 = sch->t1;
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int t2 = sch->t2;
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int t3p = sch->t3p;
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if ((t1 < 0) || (t2 < 0) || (t3p < 0))
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return -1;
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int tt;
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int t3 = t3p * 10 + 1;
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if (t3 < t2)
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tt = (t3 + 26) - t2;
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else
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tt = (t3 - t2) % 26;
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return t1 * 51 * 26 + tt * 51 + t3;
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}
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/* Parse encoded SCH message */
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int gsm_sch_parse(const uint8_t *info, struct sch_info *desc)
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{
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struct sch_packed_info *p = (struct sch_packed_info *) info;
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desc->bsic = (p->bsic[0] << 0) | (p->bsic[1] << 1) |
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(p->bsic[2] << 2) | (p->bsic[3] << 3) |
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(p->bsic[4] << 4);
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desc->t1 = (p->t1_lo[0] << 0) | (p->t1_md[0] << 1) |
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(p->t1_md[1] << 2) | (p->t1_md[2] << 3) |
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(p->t1_md[3] << 4) | (p->t1_md[4] << 5) |
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(p->t1_md[5] << 6) | (p->t1_md[6] << 7) |
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(p->t1_md[7] << 8) | (p->t1_hi[0] << 9) |
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(p->t1_hi[1] << 10);
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desc->t2 = (p->t2[0] << 0) | (p->t2[1] << 1) |
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(p->t2[2] << 2) | (p->t2[3] << 3) |
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(p->t2[4] << 4);
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desc->t3p = (p->t3p_lo[0] << 0) | (p->t3p_hi[0] << 1) |
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(p->t3p_hi[1] << 2);
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return 0;
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}
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/* From osmo-bts */
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int gsm_sch_decode(uint8_t *info, sbit_t *data)
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{
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int rc;
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ubit_t uncoded[GSM_SCH_UNCODED_LEN];
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osmo_conv_decode(&gsm_conv_sch, data, uncoded);
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rc = osmo_crc16gen_check_bits(&gsm0503_sch_crc10,
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uncoded, GSM_SCH_INFO_LEN,
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uncoded + GSM_SCH_INFO_LEN);
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if (rc)
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return -1;
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memcpy(info, uncoded, GSM_SCH_INFO_LEN * sizeof(ubit_t));
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return 0;
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}
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