osmo-bts-trx: move logical channel handlers to separate files

It's easier to maintain the logical channel handlers in separate
files, rather than in a huge one (scheduler_trx.c, ~2k lines).

Change-Id: Ie5663fd90596b4800a4546675a323250bbb24c80

1 files changed, 212 insertions, 0 deletions

diff --git a/src/osmo-bts-trx/sched_lchan_rach.c b/src/osmo-bts-trx/sched_lchan_rach.c
new file mode 100644
index 00000000..fa50f14b
--- /dev/null
+++ b/src/osmo-bts-trx/sched_lchan_rach.c
@@ -0,0 +1,212 @@
+/*
+ * (C) 2013 by Andreas Eversberg <jolly@eversberg.eu>
+ * (C) 2015-2017 by Harald Welte <laforge@gnumonks.org>
+ * (C) 2019 by Vadim Yanitskiy <axilirator@gmail.com>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 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 Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <stdint.h>
+#include <limits.h>
+#include <errno.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/coding/gsm0503_coding.h>
+
+#include <osmo-bts/bts.h>
+#include <osmo-bts/l1sap.h>
+#include <osmo-bts/logging.h>
+#include <osmo-bts/scheduler.h>
+#include <osmo-bts/scheduler_backend.h>
+
+#include <sched_utils.h>
+
+/* 3GPP TS 05.02, section 5.2.7 */
+#define RACH_EXT_TAIL_LEN	8
+#define RACH_SYNCH_SEQ_LEN	41
+
+enum rach_synch_seq_t {
+	RACH_SYNCH_SEQ_UNKNOWN = -1,
+	RACH_SYNCH_SEQ_TS0, /* GSM, GMSK (default) */
+	RACH_SYNCH_SEQ_TS1, /* EGPRS, 8-PSK */
+	RACH_SYNCH_SEQ_TS2, /* EGPRS, GMSK */
+	RACH_SYNCH_SEQ_NUM
+};
+
+static struct value_string rach_synch_seq_names[] = {
+	{ RACH_SYNCH_SEQ_UNKNOWN,	"UNKNOWN" },
+	{ RACH_SYNCH_SEQ_TS0,		"TS0: GSM, GMSK" },
+	{ RACH_SYNCH_SEQ_TS1,		"TS1: EGPRS, 8-PSK" },
+	{ RACH_SYNCH_SEQ_TS2,		"TS2: EGPRS, GMSK" },
+	{ 0, NULL },
+};
+
+static enum rach_synch_seq_t rach_get_synch_seq(sbit_t *bits, int *best_score)
+{
+	sbit_t *synch_seq_burst = bits + RACH_EXT_TAIL_LEN;
+	enum rach_synch_seq_t seq = RACH_SYNCH_SEQ_TS0;
+	int score[RACH_SYNCH_SEQ_NUM] = { 0 };
+	int max_score = INT_MIN;
+	int i, j;
+
+	/* 3GPP TS 05.02, section 5.2.7 "Access burst (AB)", synch. sequence bits */
+	static const char synch_seq_ref[RACH_SYNCH_SEQ_NUM][RACH_SYNCH_SEQ_LEN] = {
+		[RACH_SYNCH_SEQ_TS0] = "01001011011111111001100110101010001111000",
+		[RACH_SYNCH_SEQ_TS1] = "01010100111110001000011000101111001001101",
+		[RACH_SYNCH_SEQ_TS2] = "11101111001001110101011000001101101110111",
+	};
+
+	/* Get a multiplier for j-th bit of i-th synch. sequence */
+#define RACH_SYNCH_SEQ_MULT \
+	(synch_seq_ref[i][j] == '1' ? -1 : 1)
+
+	/* For each synch. sequence, count the bit match score. Since we deal with
+	 * soft-bits (-127...127), we sum the absolute values of matching ones,
+	 * and subtract the absolute values of different ones, so the resulting
+	 * score is more accurate than it could be with hard-bits. */
+	for (i = 0; i < RACH_SYNCH_SEQ_NUM; i++) {
+		for (j = 0; j < RACH_SYNCH_SEQ_LEN; j++)
+			score[i] += RACH_SYNCH_SEQ_MULT * synch_seq_burst[j];
+
+		/* Keep the maximum value updated */
+		if (score[i] > max_score) {
+			max_score = score[i];
+			seq = i;
+		}
+	}
+
+	/* Calculate an approximate level of our confidence */
+	if (best_score != NULL)
+		*best_score = max_score;
+
+	/* At least 1/3 of a synch. sequence shall match */
+	if (max_score < (127 * RACH_SYNCH_SEQ_LEN / 3))
+		return RACH_SYNCH_SEQ_UNKNOWN;
+
+	return seq;
+}
+
+int rx_rach_fn(struct l1sched_trx *l1t, enum trx_chan_type chan,
+	       uint8_t bid, const struct trx_ul_burst_ind *bi)
+{
+	struct osmo_phsap_prim l1sap;
+	int n_errors = 0;
+	int n_bits_total = 0;
+	uint16_t ra11;
+	uint8_t ra;
+	int rc;
+
+	/* TSC (Training Sequence Code) is an optional parameter of the UL burst
+	 * indication. We need this information in order to decide whether an
+	 * Access Burst is 11-bit encoded or not (see OS#1854). If this information
+	 * is absent, we try to correlate the received synch. sequence with the
+	 * known ones (3GPP TS 05.02, section 5.2.7), and fall-back to the default
+	 * TS0 if it fails. */
+	enum rach_synch_seq_t synch_seq = RACH_SYNCH_SEQ_TS0;
+	int best_score = 127 * RACH_SYNCH_SEQ_LEN;
+
+	/* If logical channel is not either of RACH, PDTCH or PTCCH, this is a
+	 * handover Access Burst, which is always encoded as 8-bit and shall
+	 * contain the generic training sequence (TS0). */
+	if (chan == TRXC_RACH || chan == TRXC_PDTCH || chan == TRXC_PTCCH) {
+		if (bi->flags & TRX_BI_F_TS_INFO)
+			synch_seq = (enum rach_synch_seq_t) bi->tsc;
+		else
+			synch_seq = rach_get_synch_seq((sbit_t *) bi->burst, &best_score);
+	}
+
+	LOGL1S(DL1P, LOGL_DEBUG, l1t, bi->tn, chan, bi->fn,
+	       "Received%s RACH (%s): rssi=%d toa256=%d",
+	       (chan != TRXC_RACH) ? " handover" : "",
+	       get_value_string(rach_synch_seq_names, synch_seq),
+	       bi->rssi, bi->toa256);
+	if (bi->flags & TRX_BI_F_CI_CB)
+		LOGPC(DL1P, LOGL_DEBUG, " C/I=%d cB", bi->ci_cb);
+	else
+		LOGPC(DL1P, LOGL_DEBUG, " match=%.1f%%",
+		      best_score * 100.0 / (127 * RACH_SYNCH_SEQ_LEN));
+	LOGPC(DL1P, LOGL_DEBUG, "\n");
+
+	/* Compose a new L1SAP primitive */
+	memset(&l1sap, 0x00, sizeof(l1sap));
+	osmo_prim_init(&l1sap.oph, SAP_GSM_PH, PRIM_PH_RACH, PRIM_OP_INDICATION, NULL);
+	l1sap.u.rach_ind.chan_nr = trx_chan_desc[chan].chan_nr | bi->tn;
+	l1sap.u.rach_ind.acc_delay = (bi->toa256 >= 0) ? bi->toa256 / 256 : 0;
+	l1sap.u.rach_ind.acc_delay_256bits = bi->toa256;
+	l1sap.u.rach_ind.rssi = bi->rssi;
+	l1sap.u.rach_ind.fn = bi->fn;
+
+	/* Link quality is defined by C/I (Carrier-to-Interference ratio),
+	 * which has optional presence. If it's absent, report the
+	 * minimum acceptable value to pass L1SAP checks. */
+	if (bi->flags & TRX_BI_F_CI_CB)
+		l1sap.u.rach_ind.lqual_cb = bi->ci_cb;
+	else
+		l1sap.u.rach_ind.lqual_cb = l1t->trx->bts->min_qual_rach;
+
+	/* Decode RACH depending on its synch. sequence */
+	switch (synch_seq) {
+	case RACH_SYNCH_SEQ_TS1:
+	case RACH_SYNCH_SEQ_TS2:
+		rc = gsm0503_rach_ext_decode_ber(&ra11, bi->burst + RACH_EXT_TAIL_LEN + RACH_SYNCH_SEQ_LEN,
+						 l1t->trx->bts->bsic, &n_errors, &n_bits_total);
+		if (rc) {
+			LOGL1S(DL1P, LOGL_DEBUG, l1t, bi->tn, chan, bi->fn,
+			       "Received bad Access Burst\n");
+			return 0;
+		}
+
+		if (synch_seq == RACH_SYNCH_SEQ_TS1)
+			l1sap.u.rach_ind.burst_type = GSM_L1_BURST_TYPE_ACCESS_1;
+		else
+			l1sap.u.rach_ind.burst_type = GSM_L1_BURST_TYPE_ACCESS_2;
+
+		l1sap.u.rach_ind.is_11bit = 1;
+		l1sap.u.rach_ind.ra = ra11;
+		break;
+
+	case RACH_SYNCH_SEQ_TS0:
+	default:
+		/* Fall-back to the default TS0 if needed */
+		if (synch_seq != RACH_SYNCH_SEQ_TS0) {
+			LOGL1S(DL1P, LOGL_DEBUG, l1t, bi->tn, chan, bi->fn,
+			       "Falling-back to the default TS0\n");
+			synch_seq = RACH_SYNCH_SEQ_TS0;
+		}
+
+		rc = gsm0503_rach_decode_ber(&ra, bi->burst + RACH_EXT_TAIL_LEN + RACH_SYNCH_SEQ_LEN,
+					     l1t->trx->bts->bsic, &n_errors, &n_bits_total);
+		if (rc) {
+			LOGL1S(DL1P, LOGL_DEBUG, l1t, bi->tn, chan, bi->fn,
+			       "Received bad Access Burst\n");
+			return 0;
+		}
+
+		l1sap.u.rach_ind.burst_type = GSM_L1_BURST_TYPE_ACCESS_0;
+		l1sap.u.rach_ind.is_11bit = 0;
+		l1sap.u.rach_ind.ra = ra;
+		break;
+	}
+
+	l1sap.u.rach_ind.ber10k = compute_ber10k(n_bits_total, n_errors);
+
+	/* forward primitive */
+	l1sap_up(l1t->trx, &l1sap);
+
+	return 0;
+}