ts,lchan_fsm: do not attempt to allocate CBCH subslots

In case a given channel combination contains a CBCH, it replaces sub-slot 2
with a CBCH, i.e. we must not attempt to allocate the same for SDCCH.

On timeslot initialization, immediately place such an lchan FSM into new state
LCHAN_ST_CBCH, so that it never appears unused and never is picked during
lchan_select(). Also set lchan->type = GSM_LCHAN_CBCH.

Verified by configuring CBCH timeslots and watching 'show lchan summary'.

Immediately after RSL and OML are up, these pchan types show lchan 2 in state
CBCH:

  BTS 0, TRX 0, Timeslot 0 CCCH+SDCCH4+CBCH, Lchan 2, Type CBCH, State CBCH - L1 MS Power: 0 dBm RXL-FULL-dl: -110 dBm RXL-FULL-ul: -110 dBm
  BTS 0, TRX 0, Timeslot 1 SDCCH8+CBCH, Lchan 2, Type CBCH, State CBCH - L1 MS Power: 0 dBm RXL-FULL-dl: -110 dBm RXL-FULL-ul: -110 dBm

With a 'phys_chan_config ccch+sdcch4+cbch' and three phones simultaneously
requesting USSD, I see:

  BTS 0, TRX 0, Timeslot 0 CCCH+SDCCH4+CBCH, Lchan 0, Type SDCCH, State ESTABLISHED - L1 MS Power: 14 dBm RXL-FULL-dl:  -53 dBm RXL-FULL-ul:  -47 dBm
  BTS 0, TRX 0, Timeslot 0 CCCH+SDCCH4+CBCH, Lchan 1, Type SDCCH, State ESTABLISHED - L1 MS Power: 30 dBm RXL-FULL-dl:  -47 dBm RXL-FULL-ul:  -47 dBm
  BTS 0, TRX 0, Timeslot 0 CCCH+SDCCH4+CBCH, Lchan 2, Type CBCH, State CBCH - L1 MS Power: 0 dBm RXL-FULL-dl: -110 dBm RXL-FULL-ul: -110 dBm
  BTS 0, TRX 0, Timeslot 0 CCCH+SDCCH4+CBCH, Lchan 3, Type SDCCH, State ESTABLISHED - L1 MS Power: 16 dBm RXL-FULL-dl:  -47 dBm RXL-FULL-ul:  -47 dBm

With 'phys_chan_config SDCCH8+CBCH' and three phones simultaneously attaching,
I see:

  BTS 0, TRX 0, Timeslot 1 SDCCH8+CBCH, Lchan 0, Type SDCCH, State WAIT_RLL_RTP_ESTABLISH - L1 MS Power: 0 dBm RXL-FULL-dl: -110 dBm RXL-FULL-ul: -110 dBm
  BTS 0, TRX 0, Timeslot 1 SDCCH8+CBCH, Lchan 1, Type SDCCH, State WAIT_RLL_RTP_ESTABLISH - L1 MS Power: 0 dBm RXL-FULL-dl: -110 dBm RXL-FULL-ul: -110 dBm
  BTS 0, TRX 0, Timeslot 1 SDCCH8+CBCH, Lchan 2, Type CBCH, State CBCH - L1 MS Power: 0 dBm RXL-FULL-dl: -110 dBm RXL-FULL-ul: -110 dBm
  BTS 0, TRX 0, Timeslot 1 SDCCH8+CBCH, Lchan 3, Type SDCCH, State WAIT_RLL_RTP_ESTABLISH - L1 MS Power: 0 dBm RXL-FULL-dl: -110 dBm RXL-FULL-ul: -110 dBm

i.e. in all cases the CBCH lchan remains occupied and is not allocated as
SDCCH.

Detaching and re-attaching the BTS reliably brings back the CBCH state. Also
verified that changing the osmo-bsc config from telnet vty and dropping oml
followed by the BTS re-attaching brings back the CBCH state.

Change-Id: I2bafc5f696e818e38f8907ad0c8f38494df0623d
changes/71/10871/2
Neels Hofmeyr 4 years ago
parent 021971781d
commit 526b4a5f35
  1. 1
      include/osmocom/bsc/lchan_fsm.h
  2. 7
      src/osmo-bsc/lchan_fsm.c
  3. 9
      src/osmo-bsc/timeslot_fsm.c

@ -14,6 +14,7 @@
enum lchan_fsm_state {
LCHAN_ST_UNUSED,
LCHAN_ST_CBCH, /*< Blocked by CBCH channel combination, not usable as SDCCH. */
LCHAN_ST_WAIT_TS_READY,
LCHAN_ST_WAIT_ACTIV_ACK, /*< After RSL Chan Act Ack, lchan is active but RTP not configured. */
LCHAN_ST_WAIT_RLL_RTP_ESTABLISH,

@ -1035,6 +1035,13 @@ static const struct osmo_fsm_state lchan_fsm_states[] = {
,
.out_state_mask = 0
| S(LCHAN_ST_WAIT_TS_READY)
| S(LCHAN_ST_CBCH)
,
},
[LCHAN_ST_CBCH] = {
.name = "CBCH",
.out_state_mask = 0
| S(LCHAN_ST_UNUSED)
,
},
[LCHAN_ST_WAIT_TS_READY] = {

@ -295,6 +295,15 @@ static void ts_fsm_unused_onenter(struct osmo_fsm_inst *fi, uint32_t prev_state)
T_CHAN_ACT_DEACT);
break;
case GSM_PCHAN_CCCH_SDCCH4_CBCH:
case GSM_PCHAN_SDCCH8_SACCH8C_CBCH:
/* For any pchans containing a CBCH, lchan[2] is reserved for CBCH and cannot be
* allocated for SDCCH. */
OSMO_ASSERT(ts->lchan[2].fi);
ts->lchan[2].type = GSM_LCHAN_CBCH;
osmo_fsm_inst_state_chg(ts->lchan[2].fi, LCHAN_ST_CBCH, 0, 0);
break;
default:
/* nothing to do */
break;

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