aboutsummaryrefslogtreecommitdiffstats
path: root/Transceiver52M/sch.c
diff options
context:
space:
mode:
Diffstat (limited to 'Transceiver52M/sch.c')
-rw-r--r--Transceiver52M/sch.c156
1 files changed, 156 insertions, 0 deletions
diff --git a/Transceiver52M/sch.c b/Transceiver52M/sch.c
new file mode 100644
index 0000000..3cc2232
--- /dev/null
+++ b/Transceiver52M/sch.c
@@ -0,0 +1,156 @@
+#include <complex.h>
+#include <stdio.h>
+#include <math.h>
+#include <string.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/conv.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/crcgen.h>
+
+#include "sch.h"
+
+/* GSM 04.08, 9.1.30 Synchronization channel information */
+struct sch_packed_info {
+ ubit_t t1_hi[2];
+ ubit_t bsic[6];
+ ubit_t t1_md[8];
+ ubit_t t3p_hi[2];
+ ubit_t t2[5];
+ ubit_t t1_lo[1];
+ ubit_t t3p_lo[1];
+} __attribute__((packed));
+
+struct sch_burst {
+ sbit_t tail0[3];
+ sbit_t data0[39];
+ sbit_t etsc[64];
+ sbit_t data1[39];
+ sbit_t tail1[3];
+ sbit_t guard[8];
+} __attribute__((packed));
+
+static const uint8_t sch_next_output[][2] = {
+ { 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+ { 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+ { 3, 0 }, { 2, 1 }, { 3, 0 }, { 2, 1 },
+ { 0, 3 }, { 1, 2 }, { 0, 3 }, { 1, 2 },
+};
+
+static const uint8_t sch_next_state[][2] = {
+ { 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
+ { 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+ { 0, 1 }, { 2, 3 }, { 4, 5 }, { 6, 7 },
+ { 8, 9 }, { 10, 11 }, { 12, 13 }, { 14, 15 },
+};
+
+static const struct osmo_conv_code gsm_conv_sch = {
+ .N = 2,
+ .K = 5,
+ .len = GSM_SCH_UNCODED_LEN,
+ .next_output = sch_next_output,
+ .next_state = sch_next_state,
+};
+
+const struct osmo_crc16gen_code gsm0503_sch_crc10 = {
+ .bits = 10,
+ .poly = 0x175,
+ .init = 0x000,
+ .remainder = 0x3ff,
+};
+
+#define GSM_MAX_BURST_LEN 157
+#define GSM_SYM_RATE (1625e3 / 6)
+
+int float_to_sbit(const float *in, sbit_t *out, float scale, int len)
+{
+ int i;
+
+ for (i = 0; i < len; i++) {
+ out[i] = (in[i] - 0.5f) * scale;
+ }
+
+ return 0;
+}
+
+/* Check if FN contains a SCH burst */
+int gsm_sch_check_fn(int fn)
+{
+ int fn51 = fn % 51;
+
+ switch (fn51) {
+ case 1:
+ case 11:
+ case 21:
+ case 31:
+ case 41:
+ return 1;
+ }
+
+ return 0;
+}
+
+/* SCH (T1, T2, T3p) to full FN value */
+int gsm_sch_to_fn(struct sch_info *sch)
+{
+ int t1 = sch->t1;
+ int t2 = sch->t2;
+ int t3p = sch->t3p;
+
+ if ((t1 < 0) || (t2 < 0) || (t3p < 0))
+ return -1;
+ int tt;
+ int t3 = t3p * 10 + 1;
+
+ if (t3 < t2)
+ tt = (t3 + 26) - t2;
+ else
+ tt = (t3 - t2) % 26;
+
+ return t1 * 51 * 26 + tt * 51 + t3;
+}
+
+/* Parse encoded SCH message */
+int gsm_sch_parse(const uint8_t *info, struct sch_info *desc)
+{
+ struct sch_packed_info *p = (struct sch_packed_info *) info;
+
+ desc->bsic = (p->bsic[0] << 0) | (p->bsic[1] << 1) |
+ (p->bsic[2] << 2) | (p->bsic[3] << 3) |
+ (p->bsic[4] << 4);
+
+ desc->t1 = (p->t1_lo[0] << 0) | (p->t1_md[0] << 1) |
+ (p->t1_md[1] << 2) | (p->t1_md[2] << 3) |
+ (p->t1_md[3] << 4) | (p->t1_md[4] << 5) |
+ (p->t1_md[5] << 6) | (p->t1_md[6] << 7) |
+ (p->t1_md[7] << 8) | (p->t1_hi[0] << 9) |
+ (p->t1_hi[1] << 10);
+
+ desc->t2 = (p->t2[0] << 0) | (p->t2[1] << 1) |
+ (p->t2[2] << 2) | (p->t2[3] << 3) |
+ (p->t2[4] << 4);
+
+ desc->t3p = (p->t3p_lo[0] << 0) | (p->t3p_hi[0] << 1) |
+ (p->t3p_hi[1] << 2);
+
+ return 0;
+}
+
+/* From osmo-bts */
+int gsm_sch_decode(uint8_t *info, sbit_t *data)
+{
+ int rc;
+ ubit_t uncoded[GSM_SCH_UNCODED_LEN];
+
+ osmo_conv_decode(&gsm_conv_sch, data, uncoded);
+
+ rc = osmo_crc16gen_check_bits(&gsm0503_sch_crc10,
+ uncoded, GSM_SCH_INFO_LEN,
+ uncoded + GSM_SCH_INFO_LEN);
+ if (rc)
+ return -1;
+
+ memcpy(info, uncoded, GSM_SCH_INFO_LEN * sizeof(ubit_t));
+
+ return 0;
+}