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-rw-r--r--gsm-tvoid/src/lib/burst_types.h213
-rw-r--r--gsm-tvoid/src/lib/conv.c487
-rw-r--r--gsm-tvoid/src/lib/conv.h42
-rwxr-xr-xgsm-tvoid/src/lib/gsm_burst.cc35
-rw-r--r--gsm-tvoid/src/lib/gsmstack.c74
-rw-r--r--gsm-tvoid/src/lib/gsmstack.h21
-rw-r--r--gsm-tvoid/src/lib/interleave.c47
-rw-r--r--gsm-tvoid/src/lib/interleave.h18
-rw-r--r--gsm-tvoid/src/lib/sch.c323
-rw-r--r--gsm-tvoid/src/lib/sch.h16
-rw-r--r--gsm-tvoid/src/lib/system.h11
11 files changed, 1286 insertions, 1 deletions
diff --git a/gsm-tvoid/src/lib/burst_types.h b/gsm-tvoid/src/lib/burst_types.h
new file mode 100644
index 0000000..90d35ad
--- /dev/null
+++ b/gsm-tvoid/src/lib/burst_types.h
@@ -0,0 +1,213 @@
+// $Id: burst_types.h,v 1.5 2007/03/14 05:44:53 jl Exp $
+
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include "gsm_constants.h"
+
+static const int TB_LEN = 3;
+static const int TB_OS1 = 0;
+static const int TB_OS2 = 145;
+static const unsigned char tail_bits[] = {0, 0, 0};
+
+/*
+ * The normal burst is used to carry information on traffic and control
+ * channels.
+ */
+static const int N_TSC_NUM = 8; // number of training sequence codes
+static const int N_TSC_CODE_LEN = 26; // length of tsc
+static const int N_TSC_OS = 61; // tsc offset
+static const int N_EDATA_LEN_1 = 58; // length of first data section
+static const int N_EDATA_OS_1 = 3; // offset of first data section
+static const int N_EDATA_LEN_2 = 58; // length of second data section
+static const int N_EDATA_OS_2 = 87; // offset of second data section
+#if 0
+static const unsigned char n_tsc[][N_TSC_CODE_LEN] = {
+/* 0 */ {
+ 0, 0, 1, 0, 0, 1, 0, 1, 1, 1, 0, 0, 0,
+ 0, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 1
+ },
+/* 1 */ {
+ 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 1,
+ 1, 1, 0, 0, 0, 1, 0, 0, 1, 0, 1, 1, 1
+ },
+/* 2 */ {
+ 0, 1, 0, 0, 0, 0, 1, 1, 1, 0, 1, 1, 1,
+ 0, 1, 0, 0, 1, 0, 0, 0, 0, 1, 1, 1, 0
+ },
+/* 3 */ {
+ 0, 1, 0, 0, 0, 1, 1, 1, 1, 0, 1, 1, 0,
+ 1, 0, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1, 0
+ },
+/* 4 */ {
+ 0, 0, 0, 1, 1, 0, 1, 0, 1, 1, 1, 0, 0,
+ 1, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1, 1
+ },
+/* 5 */ {
+ 0, 1, 0, 0, 1, 1, 1, 0, 1, 0, 1, 1, 0,
+ 0, 0, 0, 0, 1, 0, 0, 1, 1, 1, 0, 1, 0
+ },
+/* 6 */ {
+ 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 1, 1,
+ 0, 0, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1
+ },
+/* 7 */ {
+ 1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 0, 1, 0,
+ 0, 1, 0, 1, 1, 1, 0, 1, 1, 1, 1, 0, 0
+ }
+};
+
+#endif
+
+/*
+ * The frequency correction burst is used for frequency synchronization
+ * of the mobile. This is broadcast in TS0 together with the SCH and
+ * BCCH.
+ *
+ * Modulating the bits below causes a spike at 62.5kHz above (below for
+ * COMPACT) the center frequency. One can use this spike with a narrow
+ * band filter to accurately determine the center of the channel.
+ */
+static const int FC_CODE_LEN = 142;
+static const int FC_OS = 3;
+static const unsigned char fc_fb[] = {
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
+};
+
+static const unsigned char fc_compact_fb[] = {
+ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,
+ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,
+ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,
+ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,
+ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,
+ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,
+ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,
+ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0,
+ 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0, 1, 0
+};
+
+
+/*
+ * The synchronization burst is used for time synchronization of the
+ * mobile. The bits given below were chosen for their correlation
+ * properties. The synchronization channel (SCH) contains a long
+ * training sequence (given below) and carries the TDMA frame number and
+ * base station identity code. It is broadcast in TS0 in the frame
+ * following the frequency correction burst.
+ */
+static const int SB_CODE_LEN = 64;
+static const int SB_ETS_OS = 42;
+static const int SB_EDATA_LEN_1 = 39;
+static const int SB_EDATA_OS_1 = 3;
+static const int SB_EDATA_LEN_2 = 39;
+static const int SB_EDATA_OS_2 = 106;
+static const unsigned char sb_etsc[] = {
+ 1, 0, 1, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0,
+ 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1,
+ 0, 0, 1, 0, 1, 1, 0, 1, 0, 1, 0, 0, 0, 1, 0, 1,
+ 0, 1, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1
+};
+
+static const unsigned char sb_cts_etsc[] = {
+ 1, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 0, 1, 1,
+ 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 0,
+ 1, 1, 1, 1, 0, 1, 0, 0, 0, 1, 1, 1, 1, 1, 1, 0,
+ 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 1, 0, 1, 0, 1
+};
+
+static const unsigned char sb_compact_etsc[] = {
+ 1, 1, 1, 0, 1, 1, 0, 0, 0, 0, 1, 1, 0, 1, 1, 1,
+ 0, 1, 0, 1, 0, 0, 0, 1, 0, 1, 0, 1, 1, 0, 1, 0,
+ 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0,
+ 0, 0, 1, 0, 0, 0, 1, 1, 0, 1, 0, 0, 1, 1, 1, 0
+};
+
+
+/*
+ * A base tranceiver station must transmit a burst in every timeslot of
+ * every TDMA frame in channel C0. The dummy burst will be transmitted
+ * on all timeslots of all TDMA frames for which no other channel
+ * requires a burst to be transmitted.
+ */
+static const int D_CODE_LEN = 142;
+static const int D_MB_OS = 3;
+static const unsigned char d_mb[] = {
+ 1, 1, 1, 1, 1, 0, 1, 1, 0, 1, 1, 1, 0, 1, 1, 0,
+ 0, 0, 0, 0, 1, 0, 1, 0, 0, 1, 0, 0, 1, 1, 1, 0,
+ 0, 0, 0, 0, 1, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0,
+ 0, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 0, 0,
+ 0, 1, 0, 1, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 0, 0,
+ 0, 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 0, 1, 0, 1, 0,
+ 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 1, 0, 0, 1,
+ 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0, 1,
+ 0, 0, 1, 0, 1, 1, 1, 1, 1, 0, 1, 0, 1, 0
+};
+
+
+/*
+ * The access burst is used for random access from a mobile.
+ */
+static const int AB_ETB_CODE_LEN = 8;
+static const int AB_ETB_OS = 0;
+static const unsigned char ab_etb[] = {
+ 0, 0, 1, 1, 1, 0, 1, 0
+};
+
+static const int AB_SSB_CODE_LEN = 41;
+static const int AB_SSB_OS = 8;
+static const unsigned char ab_ssb[] = {
+ 0, 1, 0, 0, 1, 0, 1, 1, 0, 1, 1, 1, 1, 1, 1, 1,
+ 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 1, 0, 1, 0, 1, 0,
+ 0, 0, 1, 1, 1, 1, 0, 0, 0
+};
+
+static const unsigned char ab_ts1_ssb[] = {
+ 0, 1, 0, 1, 0, 1, 0, 0, 1, 1, 1, 1, 1, 0, 0, 0,
+ 1, 0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 1, 1, 1, 1,
+ 0, 0, 1, 0, 0, 1, 1, 0, 1
+};
+
+static const unsigned char ab_ts2_ssb[] = {
+ 1, 1, 1, 0, 1, 1, 1, 1, 0, 0, 1, 0, 0, 1, 1, 1,
+ 0, 1, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 1, 1, 0, 1,
+ 1, 0, 1, 1, 1, 0, 1, 1, 1
+};
+
+
+typedef enum {
+ burst_n_0,
+ burst_n_1,
+ burst_n_2,
+ burst_n_3,
+ burst_n_4,
+ burst_n_5,
+ burst_n_6,
+ burst_n_7,
+ burst_fc,
+ burst_fc_c,
+ burst_s,
+ burst_s_cts,
+ burst_s_c,
+ burst_d,
+ burst_a,
+ burst_a_ts1,
+ burst_a_ts2,
+ burst_not_a_burst
+} burst_t;
+
+static const int N_BURST_TYPES = ((int)(burst_not_a_burst) + 1);
+
+#ifdef __cplusplus
+}
+#endif
diff --git a/gsm-tvoid/src/lib/conv.c b/gsm-tvoid/src/lib/conv.c
new file mode 100644
index 0000000..eb97e30
--- /dev/null
+++ b/gsm-tvoid/src/lib/conv.c
@@ -0,0 +1,487 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <ctype.h>
+
+#include <math.h>
+
+//#include "burst_types.h"
+#include "conv.h"
+//#include "fire_crc.h"
+
+
+/*
+ * GSM SACCH -- Slow Associated Control Channel
+ *
+ * These messages are encoded exactly the same as on the BCCH.
+ * (Broadcast Control Channel.)
+ *
+ * Input: 184 bits
+ *
+ * 1. Add parity and flushing bits. (Output 184 + 40 + 4 = 228 bit)
+ * 2. Convolutional encode. (Output 228 * 2 = 456 bit)
+ * 3. Interleave. (Output 456 bit)
+ * 4. Map on bursts. (4 x 156 bit bursts with each 2x57 bit content data)
+ */
+
+
+/*
+ * Parity (FIRE) for the GSM SACCH channel.
+ *
+ * g(x) = (x^23 + 1)(x^17 + x^3 + 1)
+ * = x^40 + x^26 + x^23 + x^17 + x^3 + 1
+ */
+
+static const unsigned char parity_polynomial[PARITY_SIZE + 1] = {
+ 1, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 0, 1, 0,
+ 0, 1, 0, 0, 0, 0, 0, 1,
+ 0, 0, 0, 0, 0, 0, 0, 0,
+ 0, 0, 0, 0, 0, 1, 0, 0,
+ 1
+};
+
+// remainder after dividing data polynomial by g(x)
+static const unsigned char parity_remainder[PARITY_SIZE] = {
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1,
+ 1, 1, 1, 1, 1, 1, 1, 1
+};
+
+
+/*
+static void parity_encode(unsigned char *d, unsigned char *p) {
+
+ int i;
+ unsigned char buf[DATA_BLOCK_SIZE + PARITY_SIZE], *q;
+
+ memcpy(buf, d, DATA_BLOCK_SIZE);
+ memset(buf + DATA_BLOCK_SIZE, 0, PARITY_SIZE);
+
+ for(q = buf; q < buf + DATA_BLOCK_SIZE; q++)
+ if(*q)
+ for(i = 0; i < PARITY_SIZE + 1; i++)
+ q[i] ^= parity_polynomial[i];
+ for(i = 0; i < PARITY_SIZE; i++)
+ p[i] = !buf[DATA_BLOCK_SIZE + i];
+}
+ */
+
+
+int
+parity_check(unsigned char *d) {
+
+ unsigned int i;
+ unsigned char buf[DATA_BLOCK_SIZE + PARITY_SIZE], *q;
+
+ memcpy(buf, d, DATA_BLOCK_SIZE + PARITY_SIZE);
+
+ for(q = buf; q < buf + DATA_BLOCK_SIZE; q++)
+ if(*q)
+ for(i = 0; i < PARITY_SIZE + 1; i++)
+ q[i] ^= parity_polynomial[i];
+ return memcmp(buf + DATA_BLOCK_SIZE, parity_remainder, PARITY_SIZE);
+}
+
+
+/*
+ * Convolutional encoding and Viterbi decoding for the GSM SACCH channel.
+ */
+
+/*
+ * Convolutional encoding:
+ *
+ * G_0 = 1 + x^3 + x^4
+ * G_1 = 1 + x + x^3 + x^4
+ *
+ * i.e.,
+ *
+ * c_{2k} = u_k + u_{k - 3} + u_{k - 4}
+ * c_{2k + 1} = u_k + u_{k - 1} + u_{k - 3} + u_{k - 4}
+ */
+#define K 5
+#define MAX_ERROR (2 * CONV_INPUT_SIZE + 1)
+
+
+/*
+ * Given the current state and input bit, what are the output bits?
+ *
+ * encode[current_state][input_bit]
+ */
+static const unsigned int encode[1 << (K - 1)][2] = {
+ {0, 3}, {3, 0}, {3, 0}, {0, 3},
+ {0, 3}, {3, 0}, {3, 0}, {0, 3},
+ {1, 2}, {2, 1}, {2, 1}, {1, 2},
+ {1, 2}, {2, 1}, {2, 1}, {1, 2}
+};
+
+
+/*
+ * Given the current state and input bit, what is the next state?
+ *
+ * next_state[current_state][input_bit]
+ */
+static const unsigned int next_state[1 << (K - 1)][2] = {
+ {0, 8}, {0, 8}, {1, 9}, {1, 9},
+ {2, 10}, {2, 10}, {3, 11}, {3, 11},
+ {4, 12}, {4, 12}, {5, 13}, {5, 13},
+ {6, 14}, {6, 14}, {7, 15}, {7, 15}
+};
+
+
+/*
+ * Given the previous state and the current state, what input bit caused
+ * the transition? If it is impossible to transition between the two
+ * states, the value is 2.
+ *
+ * prev_next_state[previous_state][current_state]
+ */
+static const unsigned int prev_next_state[1 << (K - 1)][1 << (K - 1)] = {
+ { 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2},
+ { 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2},
+ { 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2},
+ { 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2},
+ { 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2},
+ { 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2},
+ { 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2},
+ { 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2},
+ { 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2},
+ { 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2},
+ { 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2},
+ { 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2},
+ { 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2},
+ { 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2},
+ { 2, 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1},
+ { 2, 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1}
+};
+
+
+static inline unsigned int hamming_distance2(unsigned int w) {
+
+ return (w & 1) + !!(w & 2);
+}
+
+
+/*
+static void conv_encode(unsigned char *data, unsigned char *output) {
+
+ unsigned int i, state = 0, o;
+
+ // encode data
+ for(i = 0; i < CONV_INPUT_SIZE; i++) {
+ o = encode[state][data[i]];
+ state = next_state[state][data[i]];
+ *output++ = !!(o & 2);
+ *output++ = o & 1;
+ }
+}
+ */
+
+
+int
+conv_decode(unsigned char *output, unsigned char *data) {
+
+ int i, t;
+ unsigned int rdata, state, nstate, b, o, distance, accumulated_error,
+ min_state, min_error, cur_state;
+
+ unsigned int ae[1 << (K - 1)];
+ unsigned int nae[1 << (K - 1)]; // next accumulated error
+ unsigned int state_history[1 << (K - 1)][CONV_INPUT_SIZE + 1];
+
+ // initialize accumulated error, assume starting state is 0
+ for(i = 0; i < (1 << (K - 1)); i++)
+ ae[i] = nae[i] = MAX_ERROR;
+ ae[0] = 0;
+
+ // build trellis
+ for(t = 0; t < CONV_INPUT_SIZE; t++) {
+
+ // get received data symbol
+ rdata = (data[2 * t] << 1) | data[2 * t + 1];
+
+ // for each state
+ for(state = 0; state < (1 << (K - 1)); state++) {
+
+ // make sure this state is possible
+ if(ae[state] >= MAX_ERROR)
+ continue;
+
+ // find all states we lead to
+ for(b = 0; b < 2; b++) {
+
+ // get next state given input bit b
+ nstate = next_state[state][b];
+
+ // find output for this transition
+ o = encode[state][b];
+
+ // calculate distance from received data
+ distance = hamming_distance2(rdata ^ o);
+
+ // choose surviving path
+ accumulated_error = ae[state] + distance;
+ if(accumulated_error < nae[nstate]) {
+
+ // save error for surviving state
+ nae[nstate] = accumulated_error;
+
+ // update state history
+ state_history[nstate][t + 1] = state;
+ }
+ }
+ }
+
+ // get accumulated error ready for next time slice
+ for(i = 0; i < (1 << (K - 1)); i++) {
+ ae[i] = nae[i];
+ nae[i] = MAX_ERROR;
+ }
+ }
+
+ // the final state is the state with the fewest errors
+ min_state = (unsigned int)-1;
+ min_error = MAX_ERROR;
+ for(i = 0; i < (1 << (K - 1)); i++) {
+ if(ae[i] < min_error) {
+ min_state = i;
+ min_error = ae[i];
+ }
+ }
+
+ // trace the path
+ cur_state = min_state;
+ for(t = CONV_INPUT_SIZE; t >= 1; t--) {
+ min_state = cur_state;
+ cur_state = state_history[cur_state][t]; // get previous
+ output[t - 1] = prev_next_state[cur_state][min_state];
+ }
+
+ // return the number of errors detected (hard-decision)
+ return min_error;
+}
+
+
+/*
+ * GSM SACCH interleaving and burst mapping
+ *
+ * Interleaving:
+ *
+ * Given 456 coded input bits, form 4 blocks of 114 bits:
+ *
+ * i(B, j) = c(n, k) k = 0, ..., 455
+ * n = 0, ..., N, N + 1, ...
+ * B = B_0 + 4n + (k mod 4)
+ * j = 2(49k mod 57) + ((k mod 8) div 4)
+ *
+ * Mapping on Burst:
+ *
+ * e(B, j) = i(B, j)
+ * e(B, 59 + j) = i(B, 57 + j) j = 0, ..., 56
+ * e(B, 57) = h_l(B)
+ * e(B, 58) = h_n(B)
+ *
+ * Where h_l(B) and h_n(B) are bits in burst B indicating flags.
+ */
+
+/*
+static void interleave(unsigned char *data, unsigned char *iBLOCK) {
+
+ int j, k, B;
+
+ // for each bit in input data
+ for(k = 0; k < CONV_SIZE; k++) {
+ B = k % 4;
+ j = 2 * ((49 * k) % 57) + ((k % 8) / 4);
+ iBLOCK[B * iBLOCK_SIZE + j] = data[k];
+ }
+}
+ */
+
+
+#if 0
+static void decode_interleave(unsigned char *data, unsigned char *iBLOCK) {
+
+ int j, k, B;
+
+ for(k = 0; k < CONV_SIZE; k++) {
+ B = k % 4;
+ j = 2 * ((49 * k) % 57) + ((k % 8) / 4);
+ data[k] = iBLOCK[B * iBLOCK_SIZE + j];
+ }
+}
+
+#endif
+
+/*
+static void burstmap(unsigned char *iBLOCK, unsigned char *eBLOCK,
+ unsigned char hl, unsigned char hn) {
+
+ int j;
+
+ for(j = 0; j < 57; j++) {
+ eBLOCK[j] = iBLOCK[j];
+ eBLOCK[j + 59] = iBLOCK[j + 57];
+ }
+ eBLOCK[57] = hl;
+ eBLOCK[58] = hn;
+}
+ */
+
+
+static void decode_burstmap(unsigned char *iBLOCK, unsigned char *eBLOCK,
+ unsigned char *hl, unsigned char *hn) {
+
+ int j;
+
+ for(j = 0; j < 57; j++) {
+ iBLOCK[j] = eBLOCK[j];
+ iBLOCK[j + 57] = eBLOCK[j + 59];
+ }
+ *hl = eBLOCK[57];
+ *hn = eBLOCK[58];
+}
+
+
+/*
+ * Transmitted bits are sent least-significant first.
+ */
+int
+compress_bits(unsigned char *dbuf, int dbuf_len,
+ unsigned char *sbuf, int sbuf_len) {
+
+ unsigned int i, j, c, pos = 0;
+
+ if(dbuf_len < ((sbuf_len + 7) >> 3))
+ return -1;
+
+ for(i = 0; i < sbuf_len; i += 8) {
+ for(j = 0, c = 0; (j < 8) && (i + j < sbuf_len); j++)
+ c |= (!!sbuf[i + j]) << j;
+ dbuf[pos++] = c & 0xff;
+ }
+ return pos;
+}
+
+
+#if 0
+int get_ns_l3_len(unsigned char *data, unsigned int datalen) {
+
+ if((data[0] & 3) != 1) {
+ fprintf(stderr, "error: get_ns_l3_len: pseudo-length reserved "
+ "bits bad (%2.2x)\n", data[0] & 3);
+ return -1;
+ }
+ return (data[0] >> 2);
+}
+
+#endif
+
+#if 0
+static unsigned char *decode_sacch(unsigned char *e0, unsigned char *e1,
+ unsigned char *e2, unsigned char *e3, unsigned int *datalen) {
+
+ int errors, len, data_size = (DATA_BLOCK_SIZE + 7) >> 3;
+ unsigned char conv_data[CONV_SIZE], iBLOCK[BLOCKS][iBLOCK_SIZE],
+ hl, hn, decoded_data[PARITY_OUTPUT_SIZE], *data;
+
+ if(!(data = (unsigned char *)malloc(data_size))) {
+ throw std::runtime_error("error: decode_cch: malloc");
+ }
+
+ if(datalen)
+ *datalen = 0;
+
+ // unmap the bursts
+ decode_burstmap(iBLOCK[0], e0, &hl, &hn); // XXX ignore stealing bits
+ decode_burstmap(iBLOCK[1], e1, &hl, &hn);
+ decode_burstmap(iBLOCK[2], e2, &hl, &hn);
+ decode_burstmap(iBLOCK[3], e3, &hl, &hn);
+
+ // remove interleave
+ interleave_decode(&opt.ictx, conv_data, (unsigned char *)iBLOCK);
+ //decode_interleave(conv_data, (unsigned char *)iBLOCK);
+
+ // Viterbi decode
+ errors = conv_decode(decoded_data, conv_data);
+ DEBUGF("conv_decode: %d\n", errors);
+ if (errors)
+ return NULL;
+
+ // check parity
+ // If parity check error detected try to fix it.
+ if (parity_check(decoded_data))
+ {
+ fire_crc crc(40, 184);
+ // fprintf(stderr, "error: sacch: parity error (%d)\n", errors);
+ unsigned char crc_result[224];
+ if (crc.check_crc(decoded_data, crc_result) == 0)
+ {
+ errors = -1;
+ DEBUGF("error: sacch: parity error (%d)\n", errors);
+ return NULL;
+ } else {
+ memcpy(decoded_data, crc_result, sizeof crc_result);
+ errors = 0;
+ }
+ }
+
+ if((len = compress_bits(data, data_size, decoded_data,
+ DATA_BLOCK_SIZE)) < 0) {
+ fprintf(stderr, "error: compress_bits\n");
+ return 0;
+ }
+ if(len < data_size) {
+ fprintf(stderr, "error: buf too small (%d < %d)\n",
+ sizeof(data), len);
+ return 0;
+ }
+
+ if(datalen)
+ *datalen = (unsigned int)len;
+ return data;
+}
+
+#endif
+
+/*
+ * decode_cch
+ *
+ * Decode a "common" control channel. Most control channels use
+ * the same burst, interleave, Viterbi and parity configuration.
+ * The documentation for the control channels defines SACCH first
+ * and then just keeps referring to that.
+ *
+ * The current (investigated) list is as follows:
+ *
+ * BCCH Norm
+ * BCCH Ext
+ * PCH
+ * AGCH
+ * CBCH (SDCCH/4)
+ * CBCH (SDCCH/8)
+ * SDCCH/4
+ * SACCH/C4
+ * SDCCH/8
+ * SACCH/C8
+ *
+ * We provide two functions, one for where all four bursts are
+ * contiguous, and one where they aren't.
+ */
+#if 0
+unsigned char *decode_cch(unsigned char *e0, unsigned char *e1,
+ unsigned char *e2, unsigned char *e3, unsigned int *datalen) {
+
+ return decode_sacch(e0, e1, e2, e3, datalen);
+}
+
+
+unsigned char *decode_cch(unsigned char *e, unsigned int *datalen) {
+
+ return decode_sacch(e, e + eBLOCK_SIZE, e + 2 * eBLOCK_SIZE,
+ e + 3 * eBLOCK_SIZE, datalen);
+}
+#endif
diff --git a/gsm-tvoid/src/lib/conv.h b/gsm-tvoid/src/lib/conv.h
new file mode 100644
index 0000000..0d7505d
--- /dev/null
+++ b/gsm-tvoid/src/lib/conv.h
@@ -0,0 +1,42 @@
+
+/*
+ * decode_cch
+ *
+ * Decode a "common" control channel. Most control channels use
+ * the same burst, interleave, Viterbi and parity configuration.
+ * The documentation for the control channels defines SACCH first
+ * and then just keeps referring to that.
+ *
+ * The current (investigated) list is as follows:
+ *
+ * BCCH Norm
+ * BCCH Ext
+ * PCH
+ * AGCH
+ * CBCH (SDCCH/4)
+ * CBCH (SDCCH/8)
+ * SDCCH/4
+ * SACCH/C4
+ * SDCCH/8
+ * SACCH/C8
+ *
+ * We provide two functions, one for where all four bursts are
+ * contiguous, and one where they aren't.
+ */
+
+#define DATA_BLOCK_SIZE 184
+#define PARITY_SIZE 40
+#define FLUSH_BITS_SIZE 4
+#define PARITY_OUTPUT_SIZE (DATA_BLOCK_SIZE + PARITY_SIZE + FLUSH_BITS_SIZE)
+
+#define CONV_INPUT_SIZE PARITY_OUTPUT_SIZE
+#define CONV_SIZE (2 * CONV_INPUT_SIZE)
+
+#define BLOCKS 4
+#define iBLOCK_SIZE (CONV_SIZE / BLOCKS)
+#define eBLOCK_SIZE (iBLOCK_SIZE + 2)
+
+int conv_decode(unsigned char *output, unsigned char *data);
+int parity_check(unsigned char *data);
+int compress_bits(unsigned char *dbuf, int dlen, unsigned char *src, int len);
+
diff --git a/gsm-tvoid/src/lib/gsm_burst.cc b/gsm-tvoid/src/lib/gsm_burst.cc
index f367de2..5415b2f 100755
--- a/gsm-tvoid/src/lib/gsm_burst.cc
+++ b/gsm-tvoid/src/lib/gsm_burst.cc
@@ -9,6 +9,8 @@
#include <memory.h>
#include <gsm_burst.h>
#include <assert.h>
+#include "system.h"
+#include "gsmstack.h"
gsm_burst::gsm_burst (void) :
d_bbuf_pos(0),
@@ -67,6 +69,8 @@ gsm_burst::gsm_burst (void) :
fprintf(stdout,"\n");
}
+ /* Initialize GSM Stack */
+ GS_new(&d_gs_ctx);
}
gsm_burst::~gsm_burst ()
@@ -99,6 +103,16 @@ void gsm_burst::print_bits(const float *data,int length)
data[i] < 0 ? fprintf(stdout,"+") : fprintf(stdout,".");
}
+void gsm_burst::soft2hardbit(char *dst, const float *data, int len)
+{
+ for (int i=0; i < len; i++)
+ {
+ if (data[i] < 0)
+ dst[i] = 0;
+ else
+ dst[i] = 1;
+ }
+}
void gsm_burst::print_burst(void)
{
@@ -125,13 +139,32 @@ void gsm_burst::print_burst(void)
if ( print && (d_print_options & PRINT_BITS) ) {
if (d_print_options & PRINT_ALL_BITS)
+ {
print_bits(d_burst_buffer,BBUF_SIZE);
- else
+ } else {
+ /* 142 useful bits: 2*58 + 26 training */
print_bits(d_burst_buffer + d_burst_start,USEFUL_BITS);
+ }
fprintf(stdout," ");
}
+ /*
+ * Pass information to GSM stack. GSM stack will try to extract
+ * information (fn, layer 2 messages, ...)
+ */
+
+ char buf[156];
+ /* In hardbits include the 3 trial bits */
+ /* FIXME: access burst has 8 trail bits? what is d_burst_start
+ * set to? make sure we start at the right position here.
+ */
+ soft2hardbit(buf, d_burst_buffer + d_burst_start - 3, 156);
+ /* GS_process will differentially decode the data and then
+ * extract SCH infos (and later bcch infos).
+ */
+ GS_process(&d_gs_ctx, d_ts, d_burst_type, buf);
+
if (print) {
fprintf(stdout,"%d/%d/%+d/%lu/%lu ",
diff --git a/gsm-tvoid/src/lib/gsmstack.c b/gsm-tvoid/src/lib/gsmstack.c
new file mode 100644
index 0000000..9fc4868
--- /dev/null
+++ b/gsm-tvoid/src/lib/gsmstack.c
@@ -0,0 +1,74 @@
+/*
+ * Invoke gsmstack() with any kind of burst. Automaticly decode and retrieve
+ * information.
+ */
+#include "system.h"
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include "gsmstack.h"
+#include "gsm_constants.h"
+#include "interleave.h"
+#include "sch.h"
+
+INTERLEAVE_CTX ictx;
+
+static void
+diff_decode(char *dst, char *src, int len)
+{
+ const unsigned char *end = src + len;
+ unsigned char last;
+
+ src += 3;
+ last = 0;
+ memset(dst, 0, 3);
+ dst += 3;
+
+ while (src < end)
+ {
+ *dst = !*src ^ last;
+ last = *dst;
+ src++;
+ dst++;
+ }
+}
+
+/*
+ * Initialize a new GSMSTACK context.
+ */
+int
+GS_new(GS_CTX *ctx)
+{
+ memset(ctx, 0, sizeof *ctx);
+ interleave_init(&ictx, 456, 114);
+
+ return 0;
+}
+
+/*
+ * 156 bit
+ */
+int
+GS_process(GS_CTX *ctx, int ts, int type, char *data)
+{
+ int fn;
+ int bsic;
+ int ret;
+ char buf[156];
+
+ diff_decode(buf, data, 156);
+
+ switch (type)
+ {
+ case SCH:
+ ret = decode_sch(buf, &fn, &bsic);
+ if (ret != 0)
+ break;
+ DEBUGF("FN %d, BSIC %d\n", fn, bsic);
+ break;
+ case NORMAL:
+ break;
+ }
+}
+
+
diff --git a/gsm-tvoid/src/lib/gsmstack.h b/gsm-tvoid/src/lib/gsmstack.h
new file mode 100644
index 0000000..9f0d9d8
--- /dev/null
+++ b/gsm-tvoid/src/lib/gsmstack.h
@@ -0,0 +1,21 @@
+
+#ifndef __GSMSTACK_H__
+#define __GSMSTACK_H__ 1
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+typedef struct
+{
+ int flags;
+} GS_CTX;
+
+int GS_new(GS_CTX *ctx);
+int GS_process(GS_CTX *ctx, int ts, int type, char *data);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
diff --git a/gsm-tvoid/src/lib/interleave.c b/gsm-tvoid/src/lib/interleave.c
new file mode 100644
index 0000000..437ed92
--- /dev/null
+++ b/gsm-tvoid/src/lib/interleave.c
@@ -0,0 +1,47 @@
+
+#include <stdlib.h>
+#include <stdio.h>
+#include "interleave.h"
+
+int
+interleave_init(INTERLEAVE_CTX *ictx, int size, int block_size)
+{
+ ictx->trans_size = size;
+ ictx->trans = (unsigned short *)malloc(size * sizeof *ictx->trans);
+
+// DEBUGF("size: %d\n", size);
+// DEBUGF("Block size: %d\n", block_size);
+ int j, k, B;
+ for (k = 0; k < size; k++)
+ {
+ B = k % 4;
+ j = 2 * ((49 * k) % 57) + ((k % 8) / 4);
+ ictx->trans[k] = B * block_size + j;
+ /* Mapping: pos1 goes to pos2: pos1 -> pos2 */
+// DEBUGF("%d -> %d\n", ictx->trans[k], k);
+ }
+// exit(0);
+ return 0;
+}
+
+int
+interleave_deinit(INTERLEAVE_CTX *ictx)
+{
+ if (ictx->trans != NULL)
+ {
+ free(ictx->trans);
+ ictx->trans = NULL;
+ }
+
+ return 0;
+}
+
+void
+interleave_decode(INTERLEAVE_CTX *ictx, unsigned char *dst, unsigned char *src)
+{
+
+ int k;
+ for (k = 0; k < ictx->trans_size; k++)
+ dst[k] = src[ictx->trans[k]];
+}
+
diff --git a/gsm-tvoid/src/lib/interleave.h b/gsm-tvoid/src/lib/interleave.h
new file mode 100644
index 0000000..b1abf81
--- /dev/null
+++ b/gsm-tvoid/src/lib/interleave.h
@@ -0,0 +1,18 @@
+/*
+ * $Id:$
+ */
+
+#ifndef __GSMSP_INTERLEAVE_H__
+#define __GSMSP_INTERLEAVE_H__ 1
+
+typedef struct _interleave_ctx
+{
+ unsigned short *trans;
+ int trans_size;
+} INTERLEAVE_CTX;
+
+int interleave_init(INTERLEAVE_CTX *ictx, int size, int block_size);
+int interleave_deinit(INTERLEAVE_CTX *ictx);
+void interleave_decode(INTERLEAVE_CTX *ictx, unsigned char *dst, unsigned char *src);
+
+#endif
diff --git a/gsm-tvoid/src/lib/sch.c b/gsm-tvoid/src/lib/sch.c
new file mode 100644
index 0000000..c01d7bb
--- /dev/null
+++ b/gsm-tvoid/src/lib/sch.c
@@ -0,0 +1,323 @@
+#include "system.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include "burst_types.h"
+
+/*
+ * Synchronization channel.
+ *
+ * Timeslot Repeat length Frame Number (mod repeat length)
+ * 0 51 1, 11, 21, 31, 41
+ */
+
+/*
+ * Parity (FIRE) for the GSM SCH.
+ *
+ * g(x) = x^10 + x^8 + x^6 + x^5 + x^4 + x^2 + 1
+ */
+#define DATA_BLOCK_SIZE 25
+#define PARITY_SIZE 10
+#define TAIL_BITS_SIZE 4
+#define PARITY_OUTPUT_SIZE (DATA_BLOCK_SIZE + PARITY_SIZE + TAIL_BITS_SIZE)
+
+static const unsigned char parity_polynomial[PARITY_SIZE + 1] = {
+ 1, 0, 1, 0, 1, 1, 1, 0, 1, 0, 1
+};
+
+static const unsigned char parity_remainder[PARITY_SIZE] = {
+ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1
+};
+
+
+static void parity_encode(unsigned char *d, unsigned char *p) {
+
+ unsigned int i;
+ unsigned char buf[DATA_BLOCK_SIZE + PARITY_SIZE], *q;
+
+ memcpy(buf, d, DATA_BLOCK_SIZE);
+ memset(buf + DATA_BLOCK_SIZE, 0, PARITY_SIZE);
+
+ for(q = buf; q < buf + DATA_BLOCK_SIZE; q++)
+ if(*q)
+ for(i = 0; i < PARITY_SIZE + 1; i++)
+ q[i] ^= parity_polynomial[i];
+ for(i = 0; i < PARITY_SIZE; i++)
+ p[i] = !buf[DATA_BLOCK_SIZE + i];
+}
+
+
+static int parity_check(unsigned char *d) {
+
+ unsigned int i;
+ unsigned char buf[DATA_BLOCK_SIZE + PARITY_SIZE], *q;
+
+ memcpy(buf, d, DATA_BLOCK_SIZE + PARITY_SIZE);
+
+ for(q = buf; q < buf + DATA_BLOCK_SIZE; q++)
+ if(*q)
+ for(i = 0; i < PARITY_SIZE + 1; i++)
+ q[i] ^= parity_polynomial[i];
+ return memcmp(buf + DATA_BLOCK_SIZE, parity_remainder, PARITY_SIZE);
+}
+
+
+/*
+ * Convolutional encoding and Viterbi decoding for the GSM SCH.
+ * (Equivalent to the GSM SACCH.)
+ *
+ * G_0 = 1 + x^3 + x^4
+ * G_1 = 1 + x + x^3 + x^4
+ *
+ * i.e.,
+ *
+ * c_{2k} = u_k + u_{k - 3} + u_{k - 4}
+ * c_{2k + 1} = u_k + u_{k - 1} + u_{k - 3} + u_{k - 4}
+ */
+#define CONV_INPUT_SIZE PARITY_OUTPUT_SIZE
+#define CONV_SIZE (2 * CONV_INPUT_SIZE)
+#define K 5
+#define MAX_ERROR (2 * CONV_INPUT_SIZE + 1)
+
+
+/*
+ * Given the current state and input bit, what are the output bits?
+ *
+ * encode[current_state][input_bit]
+ */
+static const unsigned int encode[1 << (K - 1)][2] = {
+ {0, 3}, {3, 0}, {3, 0}, {0, 3},
+ {0, 3}, {3, 0}, {3, 0}, {0, 3},
+ {1, 2}, {2, 1}, {2, 1}, {1, 2},
+ {1, 2}, {2, 1}, {2, 1}, {1, 2}
+};
+
+
+/*
+ * Given the current state and input bit, what is the next state?
+ *
+ * next_state[current_state][input_bit]
+ */
+static const unsigned int next_state[1 << (K - 1)][2] = {
+ {0, 8}, {0, 8}, {1, 9}, {1, 9},
+ {2, 10}, {2, 10}, {3, 11}, {3, 11},
+ {4, 12}, {4, 12}, {5, 13}, {5, 13},
+ {6, 14}, {6, 14}, {7, 15}, {7, 15}
+};
+
+
+/*
+ * Given the previous state and the current state, what input bit caused
+ * the transition? If it is impossible to transition between the two
+ * states, the value is 2.
+ *
+ * prev_next_state[previous_state][current_state]
+ */
+static const unsigned int prev_next_state[1 << (K - 1)][1 << (K - 1)] = {
+ { 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2},
+ { 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2, 2},
+ { 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2},
+ { 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2, 2},
+ { 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2},
+ { 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2, 2},
+ { 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2},
+ { 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2, 2},
+ { 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2},
+ { 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2, 2},
+ { 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2},
+ { 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2, 2},
+ { 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2},
+ { 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1, 2},
+ { 2, 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1},
+ { 2, 2, 2, 2, 2, 2, 2, 0, 2, 2, 2, 2, 2, 2, 2, 1}
+};
+
+
+static inline unsigned int hamming_distance2(unsigned int w) {
+
+ return (w & 1) + !!(w & 2);
+}
+
+
+static void conv_encode(unsigned char *data, unsigned char *output) {
+
+ unsigned int i, state = 0, o;
+
+ // encode data
+ for(i = 0; i < CONV_INPUT_SIZE; i++) {
+ o = encode[state][data[i]];
+ state = next_state[state][data[i]];
+ *output++ = !!(o & 2);
+ *output++ = o & 1;
+ }
+}
+
+
+static int conv_decode(unsigned char *data, unsigned char *output) {
+
+ int i, t;
+ unsigned int rdata, state, nstate, b, o, distance, accumulated_error,
+ min_state, min_error, cur_state;
+
+ unsigned int ae[1 << (K - 1)];
+ unsigned int nae[1 << (K - 1)]; // next accumulated error
+ unsigned int state_history[1 << (K - 1)][CONV_INPUT_SIZE + 1];
+
+ // initialize accumulated error, assume starting state is 0
+ for(i = 0; i < (1 << (K - 1)); i++)
+ ae[i] = nae[i] = MAX_ERROR;
+ ae[0] = 0;
+
+ // build trellis
+ for(t = 0; t < CONV_INPUT_SIZE; t++) {
+
+ // get received data symbol
+ rdata = (data[2 * t] << 1) | data[2 * t + 1];
+
+ // for each state
+ for(state = 0; state < (1 << (K - 1)); state++) {
+
+ // make sure this state is possible
+ if(ae[state] >= MAX_ERROR)
+ continue;
+
+ // find all states we lead to
+ for(b = 0; b < 2; b++) {
+
+ // get next state given input bit b
+ nstate = next_state[state][b];
+
+ // find output for this transition
+ o = encode[state][b];
+
+ // calculate distance from received data
+ distance = hamming_distance2(rdata ^ o);
+
+ // choose surviving path
+ accumulated_error = ae[state] + distance;
+ if(accumulated_error < nae[nstate]) {
+
+ // save error for surviving state
+ nae[nstate] = accumulated_error;
+
+ // update state history
+ state_history[nstate][t + 1] = state;
+ }
+ }
+ }
+
+ // get accumulated error ready for next time slice
+ for(i = 0; i < (1 << (K - 1)); i++) {
+ ae[i] = nae[i];
+ nae[i] = MAX_ERROR;
+ }
+ }
+
+ // the final state is the state with the fewest errors
+ min_state = (unsigned int)-1;
+ min_error = MAX_ERROR;
+ for(i = 0; i < (1 << (K - 1)); i++) {
+ if(ae[i] < min_error) {
+ min_state = i;
+ min_error = ae[i];
+ }
+ }
+
+ // trace the path
+ cur_state = min_state;
+ for(t = CONV_INPUT_SIZE; t >= 1; t--) {
+ min_state = cur_state;
+ cur_state = state_history[cur_state][t]; // get previous
+ output[t - 1] = prev_next_state[cur_state][min_state];
+ }
+
+ // return the number of errors detected (hard-decision)
+ return min_error;
+}
+
+
+int decode_sch(const unsigned char *buf, int *fn_o, int *bsic_o) {
+
+ int errors, bsic, t1, t2, t3p, t3, fn, tt;
+ unsigned char data[CONV_SIZE], decoded_data[PARITY_OUTPUT_SIZE];
+
+ // extract encoded data from synchronization burst
+ /* buf + 3, 39 bit */
+ /* buf + 3 + 39 + 64 = 106, 39 */
+ memcpy(data, buf + SB_EDATA_OS_1, SB_EDATA_LEN_1);
+ memcpy(data + SB_EDATA_LEN_1, buf + SB_EDATA_OS_2, SB_EDATA_LEN_2);
+
+ // Viterbi decode
+ if(errors = conv_decode(data, decoded_data)) {
+ // fprintf(stderr, "error: sch: conv_decode (%d)\n", errors);
+ DEBUGF("ERR: conv_decode %d\n", errors);
+ return errors;
+ }
+
+ // check parity
+ if(parity_check(decoded_data)) {
+ // fprintf(stderr, "error: sch: parity failed\n");
+ DEBUGF("ERR: parity_check failed\n");
+ return 1;
+ }
+
+ // Synchronization channel information, 44.018 page 171. (V7.2.0)
+ bsic =
+ (decoded_data[ 7] << 5) |
+ (decoded_data[ 6] << 4) |
+ (decoded_data[ 5] << 3) |
+ (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
+ if(t3 < t2)
+ tt = (t3 + 26) - t2;
+ else
+ tt = (t3 - 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)
+ *bsic_o = bsic;
+
+ return 0;
+}
diff --git a/gsm-tvoid/src/lib/sch.h b/gsm-tvoid/src/lib/sch.h
new file mode 100644
index 0000000..6fd31b8
--- /dev/null
+++ b/gsm-tvoid/src/lib/sch.h
@@ -0,0 +1,16 @@
+
+#ifndef __GSMSTACK_H__
+#define __GSMSTACK_H__ 1
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+int decode_sch(const unsigned char *src, int *fn_o, int *bsic_o);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif
+
diff --git a/gsm-tvoid/src/lib/system.h b/gsm-tvoid/src/lib/system.h
new file mode 100644
index 0000000..414730a
--- /dev/null
+++ b/gsm-tvoid/src/lib/system.h
@@ -0,0 +1,11 @@
+
+#ifndef __GSMTVOID_SYSTEM_H__
+#define __GSMTVOID_SYSTEM_H__ 1
+
+#define DEBUGF(a...) { \
+ fprintf(stderr, "%s:%d ", __FILE__, __LINE__); \
+ fprintf(stderr, a); \
+} while (0)
+
+#endif
+
personal git repositories of Harald Welte. Your mileage may vary