From aabeb2eae40bd8d5fc713fcf39e96ff14ad991b2 Mon Sep 17 00:00:00 2001
From: Max <msuraev@sysmocom.de>
Date: Fri, 4 Nov 2016 17:19:52 +0100
Subject: DTX DL AMR: rewrite FSM recursion

Add explicit state for recursion (sending the different payload data in
response to the RTS request for same FN) and corresponding
transition. Remove ST_FACCH_V as with new explicit recursion handling it
becomes unreacheable. This makes it easier to maintain
preemption (interruption of current procedure due to FACCH or
Inhibition). This also reduces the number of possible transitions out of
each state thus reducing graph's cyclomatic complexity.

Change-Id: If39b68083d23a4a35f468a5d75f54eb733ebfd14
---
 src/osmo-bts-litecell15/tch.c | 31 ++++++++++++-------------------
 1 file changed, 12 insertions(+), 19 deletions(-)

(limited to 'src/osmo-bts-litecell15/tch.c')

diff --git a/src/osmo-bts-litecell15/tch.c b/src/osmo-bts-litecell15/tch.c
index 74950738..de3c7e35 100644
--- a/src/osmo-bts-litecell15/tch.c
+++ b/src/osmo-bts-litecell15/tch.c
@@ -305,9 +305,6 @@ int l1if_tch_encode(struct gsm_lchan *lchan, uint8_t *data, uint8_t *len,
 			*payload_type = GsmL1_TchPlType_Amr;
 			rtppayload_to_l1_amr(l1_payload + 2, rtp_pl, rtp_pl_len,
 					     ft);
-			/* force STI bit to 0 to make sure resume after FACCH
-			   works properly */
-			l1_payload[6 + 2] &= ~16;
 			return 0;
 		case ST_SID_F2:
 			*payload_type = GsmL1_TchPlType_Amr;
@@ -326,7 +323,6 @@ int l1if_tch_encode(struct gsm_lchan *lchan, uint8_t *data, uint8_t *len,
 			return 1;
 		case ST_SID_U:
 			return -EAGAIN;
-		case ST_FACCH_V:
 		case ST_FACCH:
 			return -EBADMSG;
 		default:
@@ -496,19 +492,17 @@ struct msgb *gen_empty_tch_msg(struct gsm_lchan *lchan, uint32_t fn)
 	switch (lchan->tch_mode) {
 	case GSM48_CMODE_SPEECH_AMR:
 		if (lchan->type == GSM_LCHAN_TCH_H &&
-		    lchan->tch.dtx.dl_amr_fsm->state == ST_SID_F1 &&
 		    dtx_dl_amr_enabled(lchan)) {
+			/* we have to explicitly handle sending SID FIRST P2 for
+			   AMR HR in here */
 			*payload_type = GsmL1_TchPlType_Amr_SidFirstP2;
 			rc = dtx_dl_amr_fsm_step(lchan, NULL, 0, fn, l1_payload,
 						 false, &(msu_param->u8Size),
 						 NULL);
-			if (rc < 0) {
-				msgb_free(msg);
-				return NULL;
-			}
-			return msg;
-		} else
-			*payload_type = GsmL1_TchPlType_Amr;
+			if (rc == 0)
+				return msg;
+		}
+		*payload_type = GsmL1_TchPlType_Amr;
 		break;
 	case GSM48_CMODE_SPEECH_V1:
 		if (lchan->type == GSM_LCHAN_TCH_F)
@@ -524,13 +518,12 @@ struct msgb *gen_empty_tch_msg(struct gsm_lchan *lchan, uint32_t fn)
 		return NULL;
 	}
 
-	if (dtx_dl_amr_enabled(lchan)) {
-		rc = repeat_last_sid(lchan, l1_payload, fn);
-		if (!rc) {
-			msgb_free(msg);
-			return NULL;
-		}
-		msu_param->u8Size = rc;
+	rc = repeat_last_sid(lchan, l1_payload, fn);
+	if (!rc) {
+		msgb_free(msg);
+		return NULL;
 	}
+	msu_param->u8Size = rc;
+
 	return msg;
 }
-- 
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