Add high-accuracy ToA value to Uplink Measurement Reports

Normal Abis RSL MEasurement Results contain only the "MS Timing Offset
IE" in units of full symbols.  In some use cases it is important to have
higher-accuracy timing information exposed to the BSC.

We do this by adding the average timing offset value during the last
measurement interval in 1/256th symbol accuracy to the "Supplementary
MEasuremen Information" part of the TS 48.058 9.3.25 Uplink Measurements
IE.

In order to avoid any compatibility issues, this feature is only enabled
if the new vty config command "supp-meas-info toa256" at the bts node
is enabled.

Change-Id: Ie85e53b47d4041cc4e6d7b78406ae8b79b2d9397

include/osmo-bts/gsm_data_shared.h

@@ -818,6 +818,7 @@ struct gsm_bts {
 	int bcch_change_mark;
 
 	struct rate_ctr_group *ctrs;
+	bool supp_meas_toa256;
 
 	void *role;
 };

src/common/rsl.c

@@ -2400,6 +2400,7 @@ static int rsl_tx_meas_res(struct gsm_lchan *lchan, uint8_t *l3, int l3_len, con
 	uint8_t meas_res[16];
 	uint8_t chan_nr = gsm_lchan2chan_nr(lchan);
 	int res_valid = lchan->meas.flags & LC_UL_M_F_RES_VALID;
+	struct gsm_bts *bts = lchan->ts->trx->bts;
 
 	LOGP(DRSL, LOGL_DEBUG,
 	     "%s chan_num:%u Tx MEAS RES valid(%d), flags(%02x)\n",
@@ -2429,6 +2430,17 @@ static int rsl_tx_meas_res(struct gsm_lchan *lchan, uint8_t *l3, int l3_len, con
 						meas_res);
 	lchan->tch.dtx.dl_active = false;
 	if (ie_len >= 3) {
+		if (bts->supp_meas_toa256) {
+			/* append signed 16bit value containing MS timing offset in 1/256th symbols
+			 * in the vendor-specific "Supplementary Measurement Information" part of
+			 * the uplink measurements IE.  This is the current offset *relative* to the
+			 * TA which the MS has already applied.  So if you want to know the total
+			 * propagation time between MS and BTS, you need to add the actual TA value
+			 * used (from L1_INFO below, in full symbols) plus the ms_toa256 value
+			 * in 1/256 symbol periods. */
+			meas_res[ie_len++] = lchan->meas.ms_toa256 >> 8;
+			meas_res[ie_len++] = lchan->meas.ms_toa256 & 0xff;
+		}
 		msgb_tlv_put(msg, RSL_IE_UPLINK_MEAS, ie_len, meas_res);
 		lchan->meas.flags &= ~LC_UL_M_F_RES_VALID;
 	}

src/common/vty.c

@@ -295,6 +295,8 @@ static void config_write_bts_single(struct vty *vty, struct gsm_bts *bts)
 		VTY_NEWLINE);
 	if (strcmp(btsb->pcu.sock_path, PCU_SOCK_DEFAULT))
 		vty_out(vty, " pcu-socket %s%s", btsb->pcu.sock_path, VTY_NEWLINE);
+	if (bts->supp_meas_toa256)
+		vty_out(vty, " supp-meas-info toa256%s", VTY_NEWLINE);
 
 	bts_model_config_write_bts(vty, bts);
 
@@ -624,6 +626,30 @@ DEFUN(cfg_bts_pcu_sock, cfg_bts_pcu_sock_cmd,
 	return CMD_SUCCESS;
 }
 
+DEFUN(cfg_bts_supp_meas_toa256, cfg_bts_supp_meas_toa256_cmd,
+	"supp-meas-info toa256",
+	"Configure the RSL Supplementary Measurement Info\n"
+	"Report the TOA in 1/256th symbol periods\n")
+{
+	struct gsm_bts *bts = vty->index;
+	struct gsm_bts_role_bts *btsb = bts_role_bts(bts);
+
+	bts->supp_meas_toa256 = true;
+	return CMD_SUCCESS;
+}
+
+DEFUN(cfg_bts_no_supp_meas_toa256, cfg_bts_no_supp_meas_toa256_cmd,
+	"no supp-meas-info toa256",
+	NO_STR "Configure the RSL Supplementary Measurement Info\n"
+	"Report the TOA in 1/256th symbol periods\n")
+{
+	struct gsm_bts *bts = vty->index;
+	struct gsm_bts_role_bts *btsb = bts_role_bts(bts);
+
+	bts->supp_meas_toa256 = false;
+	return CMD_SUCCESS;
+}
+
 
 #define DB_DBM_STR 							\
 	"Unit is dB (decibels)\n"					\
@@ -1559,6 +1585,8 @@ int bts_vty_init(struct gsm_bts *bts, const struct log_info *cat)
 	install_element(BTS_NODE, &cfg_bts_min_qual_norm_cmd);
 	install_element(BTS_NODE, &cfg_bts_max_ber_rach_cmd);
 	install_element(BTS_NODE, &cfg_bts_pcu_sock_cmd);
+	install_element(BTS_NODE, &cfg_bts_supp_meas_toa256_cmd);
+	install_element(BTS_NODE, &cfg_bts_no_supp_meas_toa256_cmd);
 
 	install_element(BTS_NODE, &cfg_trx_gsmtap_sapi_cmd);
 	install_element(BTS_NODE, &cfg_trx_no_gsmtap_sapi_cmd);