From 53d05951a5ae0344101fccb58f89c4c1c4d2f8aa Mon Sep 17 00:00:00 2001
From: Vadim Yanitskiy <vyanitskiy@sysmocom.de>
Date: Sun, 13 Mar 2022 18:20:15 +0300
Subject: [PATCH] gsm48_make_ho_cmd(): optionally add Synchronization
 Indication IE

Change-Id: I4e5b1163a71443d706f14ce4bfd5c2294c320432
Related: SYS#5838
---
 include/osmocom/bsc/gsm_04_08_rr.h |  2 +-
 src/osmo-bsc/gsm_04_08_rr.c        | 16 ++++++++++++++--
 src/osmo-bsc/handover_fsm.c        |  2 +-
 3 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/include/osmocom/bsc/gsm_04_08_rr.h b/include/osmocom/bsc/gsm_04_08_rr.h
index 75307d63f..7d68fc85f 100644
--- a/include/osmocom/bsc/gsm_04_08_rr.h
+++ b/include/osmocom/bsc/gsm_04_08_rr.h
@@ -27,7 +27,7 @@ int gsm48_multirate_config(struct msgb *msg,
 			   const struct gsm48_multi_rate_conf *mr_conf,
 			   const struct amr_mode *modes, unsigned int num_modes);
 struct msgb *gsm48_make_ho_cmd(const struct gsm_lchan *new_lchan,
-			       enum handover_scope ho_scope,
+			       enum handover_scope ho_scope, bool async,
 			       uint8_t power_command, uint8_t ho_ref);
 int gsm48_send_rr_ass_cmd(struct gsm_lchan *dest_lchan, struct gsm_lchan *lchan, uint8_t power_command);
 int gsm48_send_rr_app_info(struct gsm_lchan *lchan, uint8_t apdu_id, uint8_t apdu_flags,
diff --git a/src/osmo-bsc/gsm_04_08_rr.c b/src/osmo-bsc/gsm_04_08_rr.c
index cf7411866..368ad733c 100644
--- a/src/osmo-bsc/gsm_04_08_rr.c
+++ b/src/osmo-bsc/gsm_04_08_rr.c
@@ -534,7 +534,7 @@ return_msg:
 
 /* Chapter 9.1.15: Handover Command */
 struct msgb *gsm48_make_ho_cmd(const struct gsm_lchan *new_lchan,
-			       enum handover_scope ho_scope,
+			       enum handover_scope ho_scope, bool async,
 			       uint8_t power_command, uint8_t ho_ref)
 {
 	struct msgb *msg = gsm48_msgb_alloc_name("GSM 04.08 HO CMD");
@@ -555,6 +555,19 @@ struct msgb *gsm48_make_ho_cmd(const struct gsm_lchan *new_lchan,
 	ho->ho_ref = ho_ref;
 	ho->power_command = power_command;
 
+	/* Synchronization Indication, TV (see 3GPP TS 44.018, 9.1.15.1).
+	 * In the case of inter-RAT handover, always include this IE for the sake of
+	 * explicitness.  In the case of intra-RAT handover, include this IE only for
+	 * the synchronized handover.  If omitted, non-synchronized handover is assumed. */
+	if (!async || (ho_scope & HO_INTER_BSC_IN)) {
+		/* Only the SI field (Non-synchronized/Synchronized) is present.
+		 * TODO: ROT (Report Observed Time Difference), currently 0.
+		 * TODO: NCI (Normal cell indication), currently 0. */
+		const uint8_t sync_ind = async ? 0x00 : 0x01;
+		/* T (4 bit) + V (4 bit), see 3GPP TS 44.018, 10.5.2.39 */
+		msgb_v_put(msg, GSM48_IE_SYNC_IND | (sync_ind & 0x0f));
+	}
+
 	if (new_lchan->ts->hopping.enabled) {
 		struct gsm48_system_information_type_1 *si1;
 
@@ -564,7 +577,6 @@ struct msgb *gsm48_make_ho_cmd(const struct gsm_lchan *new_lchan,
 				  GSM48_HOCMD_CCHDESC_LEN,
 				  si1->cell_channel_description);
 	}
-	/* FIXME: optional bits for type of synchronization? */
 
 	msgb_tv_put(msg, GSM48_IE_CHANMODE_1, new_lchan->current_ch_mode_rate.chan_mode);
 
diff --git a/src/osmo-bsc/handover_fsm.c b/src/osmo-bsc/handover_fsm.c
index b3f78c0c0..5ae3787be 100644
--- a/src/osmo-bsc/handover_fsm.c
+++ b/src/osmo-bsc/handover_fsm.c
@@ -1216,7 +1216,7 @@ static void ho_fsm_wait_rr_ho_detect_onenter(struct osmo_fsm_inst *fi, uint32_t
 	struct handover *ho = &conn->ho;
 
 	struct msgb *rr_ho_cmd = gsm48_make_ho_cmd(ho->new_lchan,
-						   ho->scope,
+						   ho->async, ho->scope,
 						   ho->new_lchan->ms_power,
 						   ho->ho_ref);
 	if (!rr_ho_cmd) {