falconia has uploaded this change for review. ( https://gerrit.osmocom.org/c/osmo-bts/+/32100 )

Change subject: sysmo: emit empty RTP ticks during FACCH stealing on TCH/F ......................................................................

sysmo: emit empty RTP ticks during FACCH stealing on TCH/F

When FACCH stealing occurs and sysmoBTS L1 delivers GsmL1_Sapi_FacchF instead of GsmL1_Sapi_TchF, that 20 ms unit still needs to be accounted for in the RTP timestamp cadence, and if we run with rtp always-output output, then an actual BFI packet needs to be emitted. The original code failed to do either; the present change implements correct behavior for TCH/F.

The case of TCH/H is still unhandled, and it may or may not be possible to handle correctly, particularly for rtp always-output mode. The fundamental difficulty is that in order to produce truly undisrupted RTP timing, two BFI packets will need to be sent for one FACCH, spaced 20 ms apart - but if the PHY only sends one GsmL1_Sapi_FacchH message surrounded by a 40 ms time gap, then we may be out of luck.

Related: OS#5974 Change-Id: I39d15faade28fb7d670493a99a0e0bdb654e2a4a --- M src/osmo-bts-sysmo/l1_if.c M src/osmo-bts-sysmo/l1_if.h M src/osmo-bts-sysmo/tch.c 3 files changed, 56 insertions(+), 0 deletions(-)

git pull ssh://gerrit.osmocom.org:29418/osmo-bts refs/changes/00/32100/1

diff --git a/src/osmo-bts-sysmo/l1_if.c b/src/osmo-bts-sysmo/l1_if.c index 646cf01..06347cf 100644 --- a/src/osmo-bts-sysmo/l1_if.c +++ b/src/osmo-bts-sysmo/l1_if.c @@ -980,6 +980,12 @@ return rc; }

+ /* If we got FACCH, the RTP clock needs to account for it, + * and if we have rtp always-output enabled, an actual BFI packet + * will be emitted. */ + if (data_ind->sapi == GsmL1_Sapi_FacchF) + l1if_tch_rx_facch(trx, chan_nr, l1p_msg); + /* fill L1SAP header */ sap_msg = l1sap_msgb_alloc(data_ind->msgUnitParam.u8Size); l1sap = msgb_l1sap_prim(sap_msg); diff --git a/src/osmo-bts-sysmo/l1_if.h b/src/osmo-bts-sysmo/l1_if.h index 8691eef..5b2da04 100644 --- a/src/osmo-bts-sysmo/l1_if.h +++ b/src/osmo-bts-sysmo/l1_if.h @@ -129,6 +129,8 @@ const uint8_t *rtp_pl, unsigned int rtp_pl_len, uint32_t fn, bool use_cache, bool marker); int l1if_tch_rx(struct gsm_bts_trx *trx, uint8_t chan_nr, struct msgb *l1p_msg); +int l1if_tch_rx_facch(struct gsm_bts_trx *trx, uint8_t chan_nr, + struct msgb *l1p_msg); int l1if_tch_fill(struct gsm_lchan *lchan, uint8_t *l1_buffer); struct msgb *gen_empty_tch_msg(struct gsm_lchan *lchan, uint32_t fn);

diff --git a/src/osmo-bts-sysmo/tch.c b/src/osmo-bts-sysmo/tch.c index 6a5d2c3..cecb4dd 100644 --- a/src/osmo-bts-sysmo/tch.c +++ b/src/osmo-bts-sysmo/tch.c @@ -625,6 +625,29 @@ return -EINVAL; }

+/*! \brief provide an RTP empty payload "tick" to upper layers upon FACCH */ +int l1if_tch_rx_facch(struct gsm_bts_trx *trx, uint8_t chan_nr, + struct msgb *l1p_msg) +{ + GsmL1_Prim_t *l1p = msgb_l1prim(l1p_msg); + GsmL1_PhDataInd_t *data_ind = &l1p->u.phDataInd; + struct msgb *rmsg = NULL; + struct gsm_lchan *lchan = &trx->ts[L1SAP_CHAN2TS(chan_nr)].lchan[l1sap_chan2ss(chan_nr)]; + + if (is_recv_only(lchan->abis_ip.speech_mode)) + return -EAGAIN; + + LOGPFN(DL1P, LOGL_DEBUG, data_ind->u32Fn, "chan_nr %d Rx FACCH\n", chan_nr); + /* Push empty payload to upper layers */ + rmsg = msgb_alloc_headroom(256, 128, "L1P-to-RTP"); + return add_l1sap_header(trx, rmsg, lchan, chan_nr, data_ind->u32Fn, + data_ind->measParam.fBer * 10000, + data_ind->measParam.fLinkQuality * 10, + 0, /* suppress RSSI like in osmo-bts-trx */ + data_ind->measParam.i16BurstTiming * 64, + 0); +} + struct msgb *gen_empty_tch_msg(struct gsm_lchan *lchan, uint32_t fn) { struct msgb *msg;