fixeria has uploaded this change for review. (
https://gerrit.osmocom.org/c/libosmocore/+/28122 )
Change subject: coding: properly handle AFS_SID_UPDATE frames in DTX mode
......................................................................
coding: properly handle AFS_SID_UPDATE frames in DTX mode
There are two similar values in enum gsm0503_amr_dtx_frames:
* AFS_SID_UPDATE - precursor of SID UPDATE,
* AFS_SID_UPDATE_CN - the actual SID UPDATE.
The former is internally used by libosmocoding to mark the current
frame as a precursor of the actual SID UPDATE frame - the later.
+---+---+---+---+---+---+---+---+
| _ | _ | _ | _ | a | b | c | d | AFS_SID_UPDATE
+---+---+---+---+---+---+---+---+
| a | b | c | d | _ | _ | _ | _ | AFS_SID_UPDATE_CN
+---+---+---+---+---+---+---+---+
This is required because function gsm0503_tch_afs_decode_dtx() is
invoked by TDMA scheduler on every 4th received burst, while the
burst buffer is 8 bursts wide.
Currently, whenever gsm0503_detect_afs_dtx_frame() detects an
AFS_SID_UPDATE frame, we still attempt to decode it as a speech
or data below in gsm0503_tch_afs_decode_dtx(). This is indeed
a bug, which results in unexpected BER values:
* expected BER 0/212,
* actual BER 252/448.
We should return immediately once we have detected an AFS_SID_UPDATE.
This patch fixes unexpected BER-SUB values during DTXu silence periods.
Change-Id: I813081a4c0865958eee2496fe251ae17235ac842
Related: SYS#5853
---
M src/coding/gsm0503_coding.c
1 file changed, 1 insertion(+), 0 deletions(-)
git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/22/28122/1
diff --git a/src/coding/gsm0503_coding.c b/src/coding/gsm0503_coding.c
index dae3a19..65141b2 100644
--- a/src/coding/gsm0503_coding.c
+++ b/src/coding/gsm0503_coding.c
@@ -2221,6 +2221,7 @@
tch_amr_reassemble(tch_data, conv, 39);
len = 5;
goto out;
+ case AFS_SID_UPDATE:
case AFS_ONSET:
len = 0;
goto out;
--
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Gerrit-Project: libosmocore
Gerrit-Branch: master
Gerrit-Change-Id: I813081a4c0865958eee2496fe251ae17235ac842
Gerrit-Change-Number: 28122
Gerrit-PatchSet: 1
Gerrit-Owner: fixeria <[email protected]>
Gerrit-MessageType: newchange
