Change in osmo-bts[master]: fix conditions for sending fill frames during RTS IND

[Harald Welte]

Harald Welte has submitted this change and it was merged. ( https://gerrit.osmocom.org/10280 )

Change subject: fix conditions for sending fill frames during RTS IND
......................................................................

fix conditions for sending fill frames during RTS IND

Rewrite an if-statement to better match the description given
in GSM 05.08, and quote the relevant paragraph in a comment.
Since this entire block of code only runs for SDCCH and TCH,
this new condition should provide the same result expect that
in accordance with the standard we now stop sending fill-frames
on a signalling TCH if DTX is in use.

Also note that this code should already cover parts of the
patch proposed at https://gerrit.osmocom.org/c/osmo-bts/+/5753
The changes to osmo-bts-litecell15/l1_if.c proposed there
should be equivalent to the fill-frame logic in this
existing common BTS code which is handling RTS IND.

Change-Id: Ibaf3ecbd0bde4f37e799d5e2f5d00dc695e0139a
Related: OS#1950
---
M src/common/l1sap.c
1 file changed, 10 insertions(+), 3 deletions(-)

Approvals:
  Harald Welte: Looks good to me, approved
  Vadim Yanitskiy: Looks good to me, but someone else must approve
  Jenkins Builder: Verified



diff --git a/src/common/l1sap.c b/src/common/l1sap.c
index 00ead8d..b8cec0e 100644
--- a/src/common/l1sap.c
+++ b/src/common/l1sap.c
@@ -754,9 +754,16 @@
 					memcpy(p + 2, si, GSM_MACBLOCK_LEN - 2);
 				} else
 					memcpy(p + 2, fill_frame, GSM_MACBLOCK_LEN - 2);
-			} else if ((!L1SAP_IS_CHAN_TCHF(chan_nr) && !L1SAP_IS_CHAN_TCHH(chan_nr))
-				|| lchan->rsl_cmode == RSL_CMOD_SPD_SIGN) {
-				/* send fill frame only, if not TCH/x != Signalling, otherwise send empty frame */
+			} else if (L1SAP_IS_CHAN_SDCCH4(chan_nr) || L1SAP_IS_CHAN_SDCCH8(chan_nr) ||
+				   (lchan->rsl_cmode == RSL_CMOD_SPD_SIGN && !lchan->ts->trx->bts->dtxd)) {
+				/*
+				 * SDCCH or TCH in signalling mode without DTX.
+				 *
+				 * Send fill frame according to GSM 05.08, section 8.3: "On the SDCCH and on the
+				 * half rate speech traffic channel in signalling only mode DTX is not allowed.
+				 * In these cases and during signalling on the TCH when DTX is not used, the same
+				 * L2 fill frame shall be transmitted in case there is nothing else to transmit."
+				 */
 				p = msgb_put(msg, GSM_MACBLOCK_LEN);
 				memcpy(p, fill_frame, GSM_MACBLOCK_LEN);
 			} /* else the message remains empty, so TCH frames are sent */

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Gerrit-Project: osmo-bts
Gerrit-Branch: master
Gerrit-MessageType: merged
Gerrit-Change-Id: Ibaf3ecbd0bde4f37e799d5e2f5d00dc695e0139a
Gerrit-Change-Number: 10280
Gerrit-PatchSet: 3
Gerrit-Owner: Stefan Sperling <ssperling at sysmocom.de>
Gerrit-Reviewer: Harald Welte <laforge at gnumonks.org>
Gerrit-Reviewer: Jenkins Builder (1000002)
Gerrit-Reviewer: Vadim Yanitskiy <axilirator at gmail.com>
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