Change in osmo-bsc[master]: lchan: pick proper power and ta values

[Neels Hofmeyr]

Neels Hofmeyr has uploaded this change for review. ( https://gerrit.osmocom.org/10701


Change subject: lchan: pick proper power and ta values
......................................................................

lchan: pick proper power and ta values

When activating an lchan, the power levels should be maximum and TA zero. Only
if a new lchan is assigned within the same cell does it make sense to take over
the previous power and TA levels.

In LCHAN_EV_ACTIVATE:

- Separate the code that copies previous encryption data. This should happen
  regardless of whether we're staying in the same cell or not.

- For the power,TA levels, take over an old lchan's values only when it is
  assigning a new lchan in the same cell.

Change-Id: I360b003398487fa6f934296ff03643c33ec61a35
---
M src/osmo-bsc/lchan_fsm.c
1 file changed, 15 insertions(+), 6 deletions(-)



  git pull ssh://gerrit.osmocom.org:29418/osmo-bsc refs/changes/01/10701/1

diff --git a/src/osmo-bsc/lchan_fsm.c b/src/osmo-bsc/lchan_fsm.c
index 3352da5..7d47380 100644
--- a/src/osmo-bsc/lchan_fsm.c
+++ b/src/osmo-bsc/lchan_fsm.c
@@ -429,6 +429,8 @@
 {
 	struct lchan_activate_info *info = data;
 	struct gsm_lchan *lchan = lchan_fi_lchan(fi);
+	struct gsm_bts *bts = lchan->ts->trx->bts;
+
 	switch (event) {
 
 	case LCHAN_EV_ACTIVATE:
@@ -446,18 +448,25 @@
 		lchan->activate.concluded = false;
 		lchan->activate.re_use_mgw_endpoint_from_lchan = info->old_lchan;
 
-		if (info->old_lchan) {
+		if (info->old_lchan)
 			lchan->encr = info->old_lchan->encr;
+		else {
+			lchan->encr = (struct gsm_encr){
+				.alg_id = RSL_ENC_ALG_A5(0),	/* no encryption */
+			};
+		}
+
+		/* If there is a previous lchan, and the new lchan is on the same cell as previous one,
+		 * take over power and TA values. Otherwise, use max power and zero TA. */
+		if (info->old_lchan && info->old_lchan->ts->trx->bts == bts) {
 			lchan->ms_power = info->old_lchan->ms_power;
 			lchan->bs_power = info->old_lchan->bs_power;
 			lchan->rqd_ta = info->old_lchan->rqd_ta;
 		} else {
-			struct gsm_bts *bts = lchan->ts->trx->bts;
-			lchan->encr = (struct gsm_encr){
-				.alg_id = RSL_ENC_ALG_A5(0),	/* no encryption */
-			};
 			lchan->ms_power = ms_pwr_ctl_lvl(bts->band, bts->ms_max_power);
-			lchan->bs_power = 0; /* 0dB reduction, output power = Pn */
+			/* From lchan_reset():
+			 * - bs_power is still zero, 0dB reduction, output power = Pn.
+			 * - TA is still zero, to be determined by RACH. */
 		}
 
 		if (info->chan_mode == GSM48_CMODE_SPEECH_AMR)

-- 
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Gerrit-Project: osmo-bsc
Gerrit-Branch: master
Gerrit-MessageType: newchange
Gerrit-Change-Id: I360b003398487fa6f934296ff03643c33ec61a35
Gerrit-Change-Number: 10701
Gerrit-PatchSet: 1
Gerrit-Owner: Neels Hofmeyr <nhofmeyr at sysmocom.de>
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