ta_control: move timing advance code from osmo-bts-trx to common

The timing advance controller that is implemented in loops.c of
osmo-bts-trx only works for osmo-bts-trx and not for any of the phy
based bts. Lets move the timing advance controller into the common part
and make it available for every bts. Also lets add a unit-test.

Change-Id: If7ddf74db3abc9b9872abe620a0aeebe3327e70a
Related: SYS#4567

1 files changed, 55 insertions, 0 deletions

diff --git a/src/common/ta_control.c b/src/common/ta_control.c
new file mode 100644
index 00000000..2ccc41a8
--- /dev/null
+++ b/src/common/ta_control.c
@@ -0,0 +1,55 @@
+/* Loop control for Timing Advance */
+
+/* (C) 2013 by Andreas Eversberg <jolly@eversberg.eu>
+ *
+ * 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 <osmo-bts/gsm_data.h>
+#include <osmo-bts/logging.h>
+
+/* 90% of one bit duration in 1/256 symbols: 256*0.9 */
+#define TOA256_9OPERCENT	230
+
+/* rqd_ta value range */
+#define TOA_MIN 0
+#define TOA_MAX 63
+
+void lchan_ms_ta_ctrl(struct gsm_lchan *lchan)
+{
+	int16_t toa256 = lchan->meas.ms_toa256;
+
+	/* Do not perform any computation when the amount of measurement
+	 * results is too little. */
+	if (lchan->meas.num_ul_meas < 4)
+		return;
+
+	if (toa256 < -TOA256_9OPERCENT && lchan->rqd_ta > TOA_MIN) {
+		LOGPLCHAN(lchan, DLOOP, LOGL_INFO,
+			  "TOA is too early (%d), now lowering TA from %d to %d\n",
+			  toa256, lchan->rqd_ta, lchan->rqd_ta - 1);
+		lchan->rqd_ta--;
+	} else if (toa256 > TOA256_9OPERCENT && lchan->rqd_ta < TOA_MAX) {
+		LOGPLCHAN(lchan, DLOOP, LOGL_INFO,
+			  "TOA is too late (%d), now raising TA from %d to %d\n",
+			  toa256, lchan->rqd_ta, lchan->rqd_ta + 1);
+		lchan->rqd_ta++;
+	} else
+		LOGPLCHAN(lchan, DLOOP, LOGL_DEBUG,
+			  "TOA is correct (%d), keeping current TA of %d\n",
+			  toa256, lchan->rqd_ta);
+}