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-rw-r--r--src/host/gprsdecode/gprs.c153
1 files changed, 153 insertions, 0 deletions
diff --git a/src/host/gprsdecode/gprs.c b/src/host/gprsdecode/gprs.c
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+++ b/src/host/gprsdecode/gprs.c
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+/*
+ * (C) 2017-2018 by sysmocom - s.f.m.c. GmbH, Author: Max <msuraev@sysmocom.de>
+ * (C) 2018 by Vadim Yanitskiy <axilirator@gmail.com>
+ * (C) 2011-2012 by Luca Melette <luca@srlabs.de>
+ *
+ * All Rights Reserved
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ * This program 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 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ */
+
+#include <stdio.h>
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <arpa/inet.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/gsmtap.h>
+#include <osmocom/coding/gsm0503_coding.h>
+
+#include "l1ctl_proto.h"
+#include "rlcmac.h"
+#include "gprs.h"
+
+/**
+ * We store both DL and UL burst buffers
+ * for all possible timeslots...
+ */
+static struct burst_buf burst_buf_dl[8] = { 0 };
+static struct burst_buf burst_buf_ul[8] = { 0 };
+
+int process_pdch(struct l1ctl_burst_ind *bi, bool verbose)
+{
+ int n_errors, n_bits_total, rc, len, i;
+ ubit_t buf[GSM_BURST_PL_LEN];
+ struct gprs_message *gm;
+ struct burst_buf *bb;
+ uint8_t l2[200];
+ uint16_t arfcn;
+ uint32_t fn;
+ uint8_t tn;
+ bool ul;
+
+ /* Get burst parameters */
+ fn = ntohl(bi->frame_nr);
+ arfcn = ntohs(bi->band_arfcn);
+ ul = !!(arfcn & GSMTAP_ARFCN_F_UPLINK);
+ tn = bi->chan_nr & 7;
+
+ /* Select a proper DL / UL buffer */
+ bb = ul ? &burst_buf_ul[tn] : &burst_buf_dl[tn];
+
+ /* Align to first frame */
+ if ((bb->count == 0) && (((fn % 13) % 4) != 0))
+ return 0;
+
+ /* Debug print */
+ if (verbose)
+ printf("Processing %s burst fn=%u, tn=%u\n",
+ ul ? "UL" : "DL", fn, tn);
+
+ /* Unpack hard-bits (1 or 0) */
+ osmo_pbit2ubit_ext(buf, 0, bi->bits, 0, 57, 0);
+ osmo_pbit2ubit_ext(buf, 59, bi->bits, 57, 57, 0);
+
+ /* Set the stealing flags */
+ buf[57] = bi->bits[14] & 0x10;
+ buf[58] = bi->bits[14] & 0x20;
+
+ /* Convert hard-bits (1 or 0) to soft-bits (-127..127) */
+ for (i = 0; i < GSM_BURST_PL_LEN; i++)
+ bb->bursts[GSM_BURST_PL_LEN * bb->count + i] = buf[i] ?
+ -(bi->snr >> 1) : (bi->snr >> 1);
+
+ /* Store the first frame number */
+ if (bb->count == 0)
+ bb->fn_first = fn;
+
+ /* Collect the measurements */
+ bb->rxl[bb->count] = bi->rx_level;
+ bb->snr[bb->count] = bi->snr;
+
+ /* Wait until complete set of bursts (4/4) */
+ if (++bb->count < 4)
+ return 0;
+
+ /* Debug print */
+ if (verbose)
+ printf("Collected 4/4 bursts on tn=%u\n", tn);
+
+ /* Flush the burst counter */
+ bb->count = 0;
+
+ /* Attempt to decode */
+ len = gsm0503_pdtch_decode(l2, bb->bursts, NULL,
+ &n_errors, &n_bits_total);
+
+ /* Debug print */
+ if (verbose)
+ printf("GSM 05.03 decoding %s (%s=%d)\n",
+ len <= 0 ? "failed" : "success",
+ len <= 0 ? "rc" : "len", len);
+
+ /* Skip bad blocks... */
+ if (len <= 0)
+ return -EIO;
+
+ /**
+ * HACK: for some reason, the handler expects
+ * 53-byte messages, while libosmocoding
+ * generates 54 bytes ?? O_o ??
+ */
+ len--;
+
+ /* Handle decoded message */
+ gm = (struct gprs_message *) malloc(sizeof(struct gprs_message) + len);
+ if (!gm)
+ return -ENOMEM;
+
+ gm->fn = bb->fn_first;
+ gm->arfcn = arfcn;
+ gm->len = len;
+ gm->tn = tn;
+
+ /* Average the measurements */
+ gm->rxl = MEAS_AVG(bb->rxl);
+ gm->snr = MEAS_AVG(bb->snr);
+
+ /* Copy the message payload */
+ memcpy(gm->msg, l2, len);
+
+ /* Handle the message */
+ rc = rlc_type_handler(gm);
+ free(gm);
+
+ return rc;
+}