1 files changed, 132 insertions, 0 deletions
diff --git a/lib/decoding/sch.c b/lib/decoding/sch.c
new file mode 100644
index 0000000..24cee30
--- /dev/null
+++ b/lib/decoding/sch.c
@@ -0,0 +1,132 @@
+/* -*- c++ -*- */
+/*
+ * @file
+ * @author 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;
+}