aboutsummaryrefslogtreecommitdiffstats
path: root/src/libbsc/chan_alloc.c
blob: 96689687816195b25076180d076cd35d68b56e05 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
/* GSM Channel allocation routines
 *
 * (C) 2008 by Harald Welte <laforge@gnumonks.org>
 * (C) 2008, 2009 by Holger Hans Peter Freyther <zecke@selfish.org>
 *
 * All Rights Reserved
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 */

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <inttypes.h>

#include <osmocom/bsc/chan_alloc.h>
#include <osmocom/bsc/abis_nm.h>
#include <osmocom/bsc/abis_rsl.h>
#include <osmocom/bsc/debug.h>
#include <osmocom/bsc/signal.h>
#include <osmocom/bsc/gsm_04_08_utils.h>

#include <osmocom/core/talloc.h>

bool ts_is_usable(const struct gsm_bts_trx_ts *ts)
{
	if (!trx_is_usable(ts->trx))
		return false;

	/* If a TCH/F_PDCH TS is busy changing, it is already taken or not
	 * yet available. */
	if (ts->pchan == GSM_PCHAN_TCH_F_PDCH) {
		if (ts->flags & TS_F_PDCH_PENDING_MASK)
			return false;
	}

	/* If a dynamic channel is busy changing, it is already taken or not
	 * yet available. */
	if (ts->pchan == GSM_PCHAN_TCH_F_TCH_H_PDCH) {
		if (ts->dyn.pchan_is != ts->dyn.pchan_want)
			return false;
	}

	return true;
}

bool trx_is_usable(const struct gsm_bts_trx *trx)
{
	/* FIXME: How does this behave for BS-11 ? */
	if (is_ipaccess_bts(trx->bts)) {
		if (!nm_is_running(&trx->mo.nm_state) ||
		    !nm_is_running(&trx->bb_transc.mo.nm_state))
			return false;
	}

	return true;
}

static int trx_count_free_ts(struct gsm_bts_trx *trx, enum gsm_phys_chan_config pchan)
{
	struct gsm_bts_trx_ts *ts;
	int j, ss;
	int count = 0;

	if (!trx_is_usable(trx))
		return 0;

	for (j = 0; j < ARRAY_SIZE(trx->ts); j++) {
		enum gsm_phys_chan_config ts_pchan_is;
		ts = &trx->ts[j];
		if (!ts_is_usable(ts))
			continue;

		ts_pchan_is = ts_pchan(ts);

		if (ts_pchan_is == GSM_PCHAN_PDCH) {
			/* Dynamic timeslots in PDCH mode will become TCH if needed. */
			switch (ts->pchan) {
			case GSM_PCHAN_TCH_F_PDCH:
				if (pchan == GSM_PCHAN_TCH_F)
					count++;
				continue;

			case GSM_PCHAN_TCH_F_TCH_H_PDCH:
				if (pchan == GSM_PCHAN_TCH_F)
					count++;
				else if (pchan == GSM_PCHAN_TCH_H)
					count += 2;
				continue;

			default:
				/* Not dynamic, not applicable. */
				continue;
			}
		}

		if (ts_pchan_is != pchan)
			continue;
		/* check if all sub-slots are allocated yet */
		for (ss = 0; ss < ts_subslots(ts); ss++) {
			struct gsm_lchan *lc = &ts->lchan[ss];
			if (lc->type == GSM_LCHAN_NONE &&
			    lc->state == LCHAN_S_NONE)
				count++;
		}
	}

	return count;
}

/* Count number of free TS of given pchan type */
int bts_count_free_ts(struct gsm_bts *bts, enum gsm_phys_chan_config pchan)
{
	struct gsm_bts_trx *trx;
	int count = 0;

	llist_for_each_entry(trx, &bts->trx_list, list)
		count += trx_count_free_ts(trx, pchan);

	return count;
}

static struct gsm_lchan *
_lc_find_trx(struct gsm_bts_trx *trx, enum gsm_phys_chan_config pchan,
	     enum gsm_phys_chan_config dyn_as_pchan)
{
	struct gsm_bts_trx_ts *ts;
	int j, start, stop, dir, ss;
	int check_subslots;

	if (!trx_is_usable(trx))
		return NULL;

	if (trx->bts->chan_alloc_reverse) {
		/* check TS 7..0 */
		start = 7;
		stop = -1;
		dir = -1;
	} else {
		/* check TS 0..7 */
		start = 0;
		stop = 8;
		dir = 1;
	}

	for (j = start; j != stop; j += dir) {
		ts = &trx->ts[j];
		if (!ts_is_usable(ts))
			continue;
		if (ts->pchan != pchan)
			continue;

		/*
		 * Allocation for fully dynamic timeslots
		 * (does not apply for ip.access style GSM_PCHAN_TCH_F_PDCH)
		 *
		 * Note the special nature of a dynamic timeslot in PDCH mode:
		 * in PDCH mode, typically, lchan->type is GSM_LCHAN_NONE and
		 * lchan->state is LCHAN_S_NONE -- an otherwise unused slot
		 * becomes PDCH implicitly. In the same sense, this channel
		 * allocator will never be asked to find an available PDCH
		 * slot; only TCH/F or TCH/H will be requested, and PDCH mode
		 * means that it is available for switchover.
		 *
		 * A dynamic timeslot in PDCH mode may be switched to TCH/F or
		 * TCH/H. If a dyn TS is already in TCH/F or TCH/H mode, it
		 * means that it is in use and its mode can't be switched.
		 *
		 * The logic concerning channels for TCH/F is trivial: there is
		 * only one channel, so a dynamic TS in TCH/F mode is already
		 * taken and not available for allocation. For TCH/H, we need
		 * to check whether a dynamic timeslot is already in TCH/H mode
		 * and whether one of the two channels is still available.
		 */
		switch (pchan) {
		case GSM_PCHAN_TCH_F_TCH_H_PDCH:
			if (ts->dyn.pchan_is != ts->dyn.pchan_want) {
				/* The TS's mode is being switched. Not
				 * available anymore/yet. */
				DEBUGP(DRLL, "%s already in switchover\n",
				       gsm_ts_and_pchan_name(ts));
				continue;
			}
			if (ts->dyn.pchan_is == GSM_PCHAN_PDCH) {
				/* This slot is available. Still check for
				 * error states to be sure; in all cases the
				 * first lchan will be used. */
				if (ts->lchan->state != LCHAN_S_NONE
				    && ts->lchan->state != LCHAN_S_ACTIVE)
					continue;
				return ts->lchan;
			}
			if (ts->dyn.pchan_is != dyn_as_pchan)
				/* not applicable. */
				continue;
			/* The requested type matches the dynamic timeslot's
			 * current mode. A channel may still be available
			 * (think TCH/H). */
			check_subslots = ts_subslots(ts);
			break;

		case GSM_PCHAN_TCH_F_PDCH:
			/* Available for voice when in PDCH mode */
			if (ts_pchan(ts) != GSM_PCHAN_PDCH)
				continue;
			/* Subslots of a PDCH ts don't need to be checked. */
			return ts->lchan;

		default:
			/* Not a dynamic channel, there is only one pchan kind: */
			check_subslots = ts_subslots(ts);
			break;
		}

		/* Is a sub-slot still available? */
		for (ss = 0; ss < check_subslots; ss++) {
			struct gsm_lchan *lc = &ts->lchan[ss];
			if (lc->type == GSM_LCHAN_NONE &&
			    lc->state == LCHAN_S_NONE)
				return lc;
		}
	}

	return NULL;
}

static struct gsm_lchan *
_lc_dyn_find_bts(struct gsm_bts *bts, enum gsm_phys_chan_config pchan,
		 enum gsm_phys_chan_config dyn_as_pchan)
{
	struct gsm_bts_trx *trx;
	struct gsm_lchan *lc;

	if (bts->chan_alloc_reverse) {
		llist_for_each_entry_reverse(trx, &bts->trx_list, list) {
			lc = _lc_find_trx(trx, pchan, dyn_as_pchan);
			if (lc)
				return lc;
		}
	} else {
		llist_for_each_entry(trx, &bts->trx_list, list) {
			lc = _lc_find_trx(trx, pchan, dyn_as_pchan);
			if (lc)
				return lc;
		}
	}

	return NULL;
}

static struct gsm_lchan *
_lc_find_bts(struct gsm_bts *bts, enum gsm_phys_chan_config pchan)
{
	return _lc_dyn_find_bts(bts, pchan, GSM_PCHAN_NONE);
}

/* Allocate a logical channel.
 *
 * Dynamic channel types: we always prefer a dedicated TS, and only pick +
 * switch a dynamic TS if no pure TS of the requested PCHAN is available.
 *
 * TCH_F/PDCH: if we pick a PDCH ACT style dynamic TS as TCH/F channel, PDCH
 * will be disabled in rsl_chan_activate_lchan(); there is no need to check
 * whether PDCH mode is currently active, here.
 */
struct gsm_lchan *lchan_alloc(struct gsm_bts *bts, enum gsm_chan_t type,
			      int allow_bigger)
{
	struct gsm_lchan *lchan = NULL;
	enum gsm_phys_chan_config first, first_cbch, second, second_cbch;

	switch (type) {
	case GSM_LCHAN_SDCCH:
		if (bts->chan_alloc_reverse) {
			first = GSM_PCHAN_SDCCH8_SACCH8C;
			first_cbch = GSM_PCHAN_SDCCH8_SACCH8C_CBCH;
			second = GSM_PCHAN_CCCH_SDCCH4;
			second_cbch = GSM_PCHAN_CCCH_SDCCH4_CBCH;
		} else {
			first = GSM_PCHAN_CCCH_SDCCH4;
			first_cbch = GSM_PCHAN_CCCH_SDCCH4_CBCH;
			second = GSM_PCHAN_SDCCH8_SACCH8C;
			second_cbch = GSM_PCHAN_SDCCH8_SACCH8C_CBCH;
		}

		lchan = _lc_find_bts(bts, first);
		if (lchan == NULL)
			lchan = _lc_find_bts(bts, first_cbch);
		if (lchan == NULL)
			lchan = _lc_find_bts(bts, second);
		if (lchan == NULL)
			lchan = _lc_find_bts(bts, second_cbch);

		/* allow to assign bigger channels */
		if (allow_bigger) {
			if (lchan == NULL) {
				lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_H);
				if (lchan)
					type = GSM_LCHAN_TCH_H;
			}

			if (lchan == NULL) {
				lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F);
				if (lchan)
					type = GSM_LCHAN_TCH_F;
			}

			/* try dynamic TCH/F_PDCH */
			if (lchan == NULL) {
				lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F_PDCH);
				/* TCH/F_PDCH will be used as TCH/F */
				if (lchan)
					type = GSM_LCHAN_TCH_F;
			}

			/* try fully dynamic TCH/F_TCH/H_PDCH */
			if (lchan == NULL) {
				lchan = _lc_dyn_find_bts(bts, GSM_PCHAN_TCH_F_TCH_H_PDCH,
							 GSM_PCHAN_TCH_H);
				if (lchan)
					type = GSM_LCHAN_TCH_H;
			}
			/*
			 * No need to check fully dynamic channels for TCH/F:
			 * if no TCH/H was available, neither will be TCH/F.
			 */
		}
		break;
	case GSM_LCHAN_TCH_F:
		lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F);
		/* If we don't have TCH/F available, fall-back to TCH/H */
		if (!lchan) {
			lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_H);
			if (lchan)
				type = GSM_LCHAN_TCH_H;
		}
		/* If we don't have TCH/H either, try dynamic TCH/F_PDCH */
		if (!lchan) {
			lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F_PDCH);
			/* TCH/F_PDCH used as TCH/F -- here, type is already
			 * set to GSM_LCHAN_TCH_F, but for clarity's sake... */
			if (lchan)
				type = GSM_LCHAN_TCH_F;
		}

		/* Try fully dynamic TCH/F_TCH/H_PDCH as TCH/F... */
		if (!lchan && bts->network->dyn_ts_allow_tch_f) {
			lchan = _lc_dyn_find_bts(bts,
						 GSM_PCHAN_TCH_F_TCH_H_PDCH,
						 GSM_PCHAN_TCH_F);
			if (lchan)
				type = GSM_LCHAN_TCH_F;
		}
		/* ...and as TCH/H. */
		if (!lchan) {
			lchan = _lc_dyn_find_bts(bts,
						 GSM_PCHAN_TCH_F_TCH_H_PDCH,
						 GSM_PCHAN_TCH_H);
			if (lchan)
				type = GSM_LCHAN_TCH_H;
		}
		break;
	case GSM_LCHAN_TCH_H:
		lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_H);
		/* If we don't have TCH/H available, fall-back to TCH/F */
		if (!lchan) {
			lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F);
			if (lchan)
				type = GSM_LCHAN_TCH_F;
		}
		/* No dedicated TCH/x available -- try fully dynamic
		 * TCH/F_TCH/H_PDCH */
		if (!lchan) {
			lchan = _lc_dyn_find_bts(bts,
						 GSM_PCHAN_TCH_F_TCH_H_PDCH,
						 GSM_PCHAN_TCH_H);
			if (lchan)
				type = GSM_LCHAN_TCH_H;
		}
		/*
		 * No need to check TCH/F_TCH/H_PDCH channels for TCH/F:
		 * if no TCH/H was available, neither will be TCH/F.
		 */
		/* If we don't have TCH/F either, try dynamic TCH/F_PDCH */
		if (!lchan) {
			lchan = _lc_find_bts(bts, GSM_PCHAN_TCH_F_PDCH);
			if (lchan)
				type = GSM_LCHAN_TCH_F;
		}
		break;
	default:
		LOGP(DRLL, LOGL_ERROR, "Unknown gsm_chan_t %u\n", type);
	}

	if (lchan) {
		lchan->type = type;

		LOGP(DRLL, LOGL_INFO, "%s Allocating lchan=%u as %s\n",
		     gsm_ts_and_pchan_name(lchan->ts),
		     lchan->nr, gsm_lchant_name(lchan->type));

		/* reset measurement report counter and index */
	        lchan->meas_rep_count = 0;
	        lchan->meas_rep_idx = 0;
	        lchan->meas_rep_last_seen_nr = 255;

		/* clear sapis */
		memset(lchan->sapis, 0, ARRAY_SIZE(lchan->sapis));

		/* clear multi rate config */
		memset(&lchan->mr_ms_lv, 0, sizeof(lchan->mr_ms_lv));
		memset(&lchan->mr_bts_lv, 0, sizeof(lchan->mr_bts_lv));
		lchan->broken_reason = "";
	} else {
		struct challoc_signal_data sig;

		LOGP(DRLL, LOGL_ERROR, "Failed to allocate %s channel\n",
		     gsm_lchant_name(type));

		sig.bts = bts;
		sig.type = type;
		osmo_signal_dispatch(SS_CHALLOC, S_CHALLOC_ALLOC_FAIL, &sig);
	}

	return lchan;
}

/* Free a logical channel */
void lchan_free(struct gsm_lchan *lchan)
{
	struct challoc_signal_data sig;
	int i;

	sig.type = lchan->type;
	lchan->type = GSM_LCHAN_NONE;


	if (lchan->conn
	    && !(lchan->ts->pchan == GSM_PCHAN_TCH_F_TCH_H_PDCH
		 && lchan->ts->dyn.pchan_is != lchan->ts->dyn.pchan_want)) {
		struct lchan_signal_data sig;

		/* We might kill an active channel... */
		sig.lchan = lchan;
		sig.mr = NULL;
		osmo_signal_dispatch(SS_LCHAN, S_LCHAN_UNEXPECTED_RELEASE, &sig);
	}

	/* stop the timer */
	osmo_timer_del(&lchan->T3101);

	/* clear cached measuement reports */
	lchan->meas_rep_idx = 0;
	for (i = 0; i < ARRAY_SIZE(lchan->meas_rep); i++) {
		lchan->meas_rep[i].flags = 0;
		lchan->meas_rep[i].nr = 0;
	}
	for (i = 0; i < ARRAY_SIZE(lchan->neigh_meas); i++)
		lchan->neigh_meas[i].arfcn = 0;

	if (lchan->rqd_ref) {
		talloc_free(lchan->rqd_ref);
		lchan->rqd_ref = NULL;
		lchan->rqd_ta = 0;
	}

	sig.lchan = lchan;
	sig.bts = lchan->ts->trx->bts;
	osmo_signal_dispatch(SS_CHALLOC, S_CHALLOC_FREED, &sig);

	if (lchan->conn
	    && !(lchan->ts->pchan == GSM_PCHAN_TCH_F_TCH_H_PDCH
		 && lchan->ts->dyn.pchan_is != lchan->ts->dyn.pchan_want)) {
		LOGP(DRLL, LOGL_ERROR, "the subscriber connection should be gone.\n");
		lchan->conn = NULL;
	}

	/* FIXME: ts_free() the timeslot, if we're the last logical
	 * channel using it */
}

/*
 * There was an error with the TRX and we need to forget
 * any state so that a lchan can be allocated again after
 * the trx is fully usable.
 *
 * This should be called after lchan_free to force a channel
 * be available for allocation again. This means that this
 * method will stop the "delay after error"-timer and set the
 * state to LCHAN_S_NONE.
 */
void lchan_reset(struct gsm_lchan *lchan)
{
	osmo_timer_del(&lchan->T3101);
	osmo_timer_del(&lchan->T3109);
	osmo_timer_del(&lchan->T3111);
	osmo_timer_del(&lchan->error_timer);

	lchan->type = GSM_LCHAN_NONE;
	rsl_lchan_set_state(lchan, LCHAN_S_NONE);
}

/* Drive the release process of the lchan */
static void _lchan_handle_release(struct gsm_lchan *lchan,
				  int sacch_deact, int mode)
{
	/* Release all SAPIs on the local end and continue */
	rsl_release_sapis_from(lchan, 1, RSL_REL_LOCAL_END);

	/*
	 * Shall we send a RR Release, start T3109 and wait for the
	 * release indication from the BTS or just take it down (e.g.
	 * on assignment requests)
	 */
	if (sacch_deact) {
		gsm48_send_rr_release(lchan);

		/* Deactivate the SACCH on the BTS side */
		rsl_deact_sacch(lchan);
		rsl_start_t3109(lchan);
	} else if (lchan->sapis[0] == LCHAN_SAPI_UNUSED) {
		rsl_direct_rf_release(lchan);
	} else {
		rsl_release_request(lchan, 0, mode);
	}
}

/* Consider releasing the channel now */
int lchan_release(struct gsm_lchan *lchan, int sacch_deact, enum rsl_rel_mode mode)
{
	DEBUGP(DRLL, "%s starting release sequence\n", gsm_lchan_name(lchan));
	rsl_lchan_set_state(lchan, LCHAN_S_REL_REQ);

	lchan->conn = NULL;
	_lchan_handle_release(lchan, sacch_deact, mode);
	return 1;
}

void bts_chan_load(struct pchan_load *cl, const struct gsm_bts *bts)
{
	struct gsm_bts_trx *trx;

	llist_for_each_entry(trx, &bts->trx_list, list) {
		int i;

		/* skip administratively deactivated tranxsceivers */
		if (!nm_is_running(&trx->mo.nm_state) ||
		    !nm_is_running(&trx->bb_transc.mo.nm_state))
			continue;

		for (i = 0; i < ARRAY_SIZE(trx->ts); i++) {
			struct gsm_bts_trx_ts *ts = &trx->ts[i];
			struct load_counter *pl = &cl->pchan[ts->pchan];
			int j;
			int subslots;

			/* skip administratively deactivated timeslots */
			if (!nm_is_running(&ts->mo.nm_state))
				continue;

			subslots = ts_subslots(ts);
			for (j = 0; j < subslots; j++) {
				struct gsm_lchan *lchan = &ts->lchan[j];

				pl->total++;

				switch (lchan->state) {
				case LCHAN_S_NONE:
					break;
				default:
					pl->used++;
					break;
				}
			}
		}
	}
}

void network_chan_load(struct pchan_load *pl, struct gsm_network *net)
{
	struct gsm_bts *bts;

	memset(pl, 0, sizeof(*pl));

	llist_for_each_entry(bts, &net->bts_list, list)
		bts_chan_load(pl, bts);
}

/* Update T3122 wait indicator based on samples of BTS channel load. */
void
bts_update_t3122_chan_load(struct gsm_bts *bts)
{
	struct pchan_load pl;
	uint64_t used = 0;
	uint32_t total = 0;
	uint64_t load;
	uint64_t wait_ind;
	static const uint8_t min_wait_ind = GSM_T3122_DEFAULT;
	static const uint8_t max_wait_ind = 128; /* max wait ~2 minutes */
	int i;

	/* Ignore BTS that are not in operation, in order to not flood the log with "bogus channel load"
	 * messages */
	if (!trx_is_usable(bts->c0))
		return;

	/* Sum up current load across all channels. */
	memset(&pl, 0, sizeof(pl));
	bts_chan_load(&pl, bts);
	for (i = 0; i < ARRAY_SIZE(pl.pchan); i++) {
		struct load_counter *lc = &pl.pchan[i];

		/* Ignore samples too large for fixed-point calculations (shouldn't happen). */
		if (lc->used > UINT16_MAX || lc->total > UINT16_MAX) {
			LOGP(DRLL, LOGL_NOTICE, "(bts=%d) numbers in channel load sample "
			     "too large (used=%u / total=%u)\n", bts->nr, lc->used, lc->total);
			continue;
		}

		used += lc->used;
		total += lc->total;
	}

	/* Check for invalid samples (shouldn't happen). */
	if (total == 0 || used > total) {
		LOGP(DRLL, LOGL_NOTICE, "(bts=%d) bogus channel load sample (used=%"PRIu64" / total=%"PRIu32")\n",
		     bts->nr, used, total);
		bts->T3122 = 0; /* disable override of network-wide default value */
		bts->chan_load_samples_idx = 0; /* invalidate other samples collected so far */
		return;
	}

	/* If we haven't got enough samples yet, store measurement for later use. */
	if (bts->chan_load_samples_idx < ARRAY_SIZE(bts->chan_load_samples)) {
		struct load_counter *sample = &bts->chan_load_samples[bts->chan_load_samples_idx++];
		sample->total = (unsigned int)total;
		sample->used = (unsigned int)used;
		return;
	}

	/* We have enough samples and will overwrite our current samples later. */
	bts->chan_load_samples_idx = 0;

	/* Add all previous samples to the current sample. */
	for (i = 0; i < ARRAY_SIZE(bts->chan_load_samples); i++) {
		struct load_counter *sample = &bts->chan_load_samples[i];
		total += sample->total;
		used += sample->used;
	}

	used <<= 8; /* convert to fixed-point */

	/* Log channel load average. */
	load = ((used / total) * 100);
	LOGP(DRLL, LOGL_DEBUG, "(bts=%d) channel load average is %"PRIu64".%.2"PRIu64"%%\n",
	     bts->nr, (load & 0xffffff00) >> 8, (load & 0xff) / 10);
	bts->chan_load_avg = ((load & 0xffffff00) >> 8);
	OSMO_ASSERT(bts->chan_load_avg <= 100);
	osmo_stat_item_set(bts->bts_statg->items[BTS_STAT_CHAN_LOAD_AVERAGE], bts->chan_load_avg);

	/* Calculate new T3122 wait indicator. */
	wait_ind = ((used / total) * max_wait_ind);
	wait_ind >>= 8; /* convert from fixed-point to integer */
	if (wait_ind < min_wait_ind)
		wait_ind = min_wait_ind;
	else if (wait_ind > max_wait_ind)
		wait_ind = max_wait_ind;

	LOGP(DRLL, LOGL_DEBUG, "(bts=%d) T3122 wait indicator set to %"PRIu64" seconds\n", bts->nr, wait_ind);
	bts->T3122 = (uint8_t)wait_ind;
	osmo_stat_item_set(bts->bts_statg->items[BTS_STAT_T3122], wait_ind);
}