initial acc ramping implementation (untested)

Change-Id: I2b1868765346c7aba966cecd7b8db9aae9b047bb

6 files changed, 163 insertions, 17 deletions

diff --git a/include/osmocom/bsc/acc_ramp.h b/include/osmocom/bsc/acc_ramp.h
index ad31f8f56..39f10ccad 100644
--- a/include/osmocom/bsc/acc_ramp.h
+++ b/include/osmocom/bsc/acc_ramp.h
@@ -44,10 +44,12 @@ enum acc_ramp_step_interval {
 };
 
 struct acc_ramp {
+	struct gsm_bts *bts; /* backpointer to BTS using this ACC ramp */
+
 	/*
-	 * Bitmasks which keep track of access control classes that are currently
-	 * denied access to this BTS. These masks modulate bits from octets 2 and 3
-	 * of the RACH Control Parameters (see 3GPP 44.018 10.5.2.29).
+	 * Bitmasks which keep track of access control classes that are currently denied
+	 * access. These masks should be used to modulate bits from octets 2 and 3 of
+	 * the RACH Control Parameters (see 3GPP 44.018 10.5.2.29).
 	 * While a bit in these masks is set, the corresponding ACC is barred.
 	 * Note that t2 contains bits for classes 11-15 which should always be allowed,
 	 * and a bit which denies emergency calls for all ACCs from 0-9 inclusive.
@@ -74,8 +76,55 @@ struct acc_ramp {
 	struct osmo_timer_list step_timer;
 };
 
-void acc_ramp_init(struct acc_ramp *acc_ramp);
+/*
+ * Initialize an acc_ramp data structure.
+ * Storage for this structure must be provided by the caller.
+ * The BTS which uses this ACC ramp must be provided as well to allow for automatic
+ * scaling of the timeout imterval based on BTS channel load average.
+ * All ACCs are allowed by default. Call acc_ramp_start() next to initiate the ramping process.
+ */
+void acc_ramp_init(struct acc_ramp *acc_ramp, struct gsm_bts *bts);
+
+/* Change the ramping step size. Returns negative on error (step_size out of range), else zero. */
+int acc_ramp_set_step_size(struct acc_ramp *acc_ramp, enum acc_ramp_step_size step_size);
+
+/*
+ * Change the ramping step interval to a fixed value. Unless this function is called,
+ * the interval is automatically scaled to the BTS channel load average.
+ */
+int acc_ramp_set_step_interval(struct acc_ramp *acc_ramp, unsigned int step_interval);
+
+/*
+ * Clear a previously set fixed ramping step interval, so that the interval
+ * is again automatically scaled to the BTS channel load average.
+ */
+void acc_ramp_set_step_interval_dynamic(struct acc_ramp *acc_ramp);
+
+/*
+ * Begin the ramping process. This initially sets all ACCs to denied, and then
+ * performs at least one ramping step to allow 'step_size' ACCs.
+ * If 'step_size' is ACC_RAMP_STEP_SIZE_MAX, all ACCs will be allowed immediately,
+ * i.e. ACC ramping becomes a no-op.
+ */
 void acc_ramp_start(struct acc_ramp *acc_ramp);
-void acc_ramp_stop(struct acc_ramp *acc_ramp);
+
+/* Abort the ramping process. If the process has already finished, this function has no effect. */
+void acc_ramp_abort(struct acc_ramp *acc_ramp);
+
+/*
+ * Return bitmasks which correspond to access control classes which are currently
+ * denied access. Ramping is only concerned with those bits which control access
+ * for ACCs 0-9, and any of the other bits will always be set to zero in these masks, i.e.
+ * it is safe to OR these bitmasks with the corresponding fields in struct gsm48_rach_control.
+ */
+static inline uint8_t acc_ramp_get_barred_t2(struct acc_ramp *acc_ramp)
+{
+	return (acc_ramp->barred_t2 & 0x03);
+};
+
+static inline uint8_t acc_ramp_get_barred_t3(struct acc_ramp *acc_ramp)
+{
+	return acc_ramp->barred_t3;
+}
 
 #endif /* _ACC_RAMP_H_ */
diff --git a/include/osmocom/bsc/gsm_data_shared.h b/include/osmocom/bsc/gsm_data_shared.h
index cf93b620b..9fa6d8318 100644
--- a/include/osmocom/bsc/gsm_data_shared.h
+++ b/include/osmocom/bsc/gsm_data_shared.h
@@ -819,6 +819,7 @@ struct gsm_bts {
 	/* Periodic channel load measurements are used to maintain T3122. */
 	struct load_counter chan_load_samples[7];
 	int chan_load_samples_idx;
+	uint8_t chan_load_avg; /* current channel load average in percent (0 - 100). */
 };
 
 
diff --git a/src/libbsc/chan_alloc.c b/src/libbsc/chan_alloc.c
index 500ad5958..40cca93d8 100644
--- a/src/libbsc/chan_alloc.c
+++ b/src/libbsc/chan_alloc.c
@@ -656,8 +656,10 @@ bts_update_t3122_chan_load(struct gsm_bts *bts)
 	load = ((used / total) * 100);
 	LOGP(DRLL, LOGL_DEBUG, "(bts=%d) channel load average is %lu.%.2lu%%\n",
 	     bts->nr, (load & 0xffffff00) >> 8, (load & 0xff) / 10);
-	osmo_stat_item_set(bts->bts_statg->items[BTS_STAT_CHAN_LOAD_AVERAGE],
-			   (load & 0xffffff00) >> 8);
+	bts->chan_load_avg = ((load & 0xffffff00) >> 8);
+	if (bts->chan_load_avg > 100) /* sanity check; should not happen */
+		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);
diff --git a/src/libcommon/acc_ramp.c b/src/libcommon/acc_ramp.c
index c8574be2a..124ce8b00 100644
--- a/src/libcommon/acc_ramp.c
+++ b/src/libcommon/acc_ramp.c
@@ -17,31 +17,123 @@
  *
  */
 
+#include <strings.h>
+#include <errno.h>
+
+#include <osmocom/bsc/debug.h>
 #include <osmocom/bsc/acc_ramp.h>
+#include <osmocom/bsc/gsm_data.h>
 
-static void acc_ramp_timer_step(void *data)
+static void deny_all_accs(struct acc_ramp *acc_ramp)
 {
-	struct acc_ramp *acc_ramp = data;
+	acc_ramp->barred_t2 = 0x03; /* AC8, AC9 barred */
+	acc_ramp->barred_t3 = 0xff; /* AC0 - AC7 barred */
 }
 
-void acc_ramp_init(struct acc_ramp *acc_ramp)
+static void allow_all_accs(struct acc_ramp *acc_ramp)
 {
-	acc_ramp->barred_t2 = 0x03; /* AC8, AC9 barred */
-	acc_ramp->barred_t3 = 0xff; /* AC0 - AC7 barred */
+	acc_ramp->barred_t2 = 0x00; /* AC8, AC9 allowed */
+	acc_ramp->barred_t3 = 0x00; /* AC0 - AC7 allowed */
+}
+
+static unsigned int get_next_step_interval(struct acc_ramp *acc_ramp)
+{
+	struct gsm_bts *bts = acc_ramp->bts;
+
+	if (acc_ramp->step_interval_is_fixed)
+		return acc_ramp->step_interval_sec;
+
+	if (bts->chan_load_avg == 0) {
+		acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_MIN;
+	} else {
+		/* Scale the step interval to current channel load average. */
+		uint64_t load = (bts->chan_load_avg << 8); /* convert to fixed-point */
+		acc_ramp->step_interval_sec = ((load * ACC_RAMP_STEP_INTERVAL_MAX) / 100) >> 8;
+		if (acc_ramp->step_interval_sec < ACC_RAMP_STEP_SIZE_MIN)
+			acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_MIN;
+		else if (acc_ramp->step_interval_sec > ACC_RAMP_STEP_INTERVAL_MAX)
+			acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_MAX;
+	}
+
+	LOGP(DRLL, LOGL_DEBUG, "(bts=%d) ACC ramp interval set to %u sec based on %u%% load average\n",
+	     bts->nr, acc_ramp->step_interval_sec, bts->chan_load_avg);
+	return acc_ramp->step_interval_sec;
+}
+
+static void acc_ramping_step(void *data)
+{
+	struct acc_ramp *acc_ramp = data;
+	int i;
+
+	/* Shortcut in case we only do one ramping step. */
+	if (acc_ramp->step_size == ACC_RAMP_STEP_SIZE_MAX) {
+		allow_all_accs(acc_ramp);
+		return;
+	}
 
+	/* Allow 'step_size' ACCs, starting from ACC0. ACC9 will be allowed last. */
+	for (i = 0; i < acc_ramp->step_size; i++) {
+		int c = ffs(acc_ramp->barred_t3);
+		if (c <= 0) {
+			c = ffs(acc_ramp->barred_t2);
+			if (c > 0 && c <= 2)
+				acc_ramp->barred_t2 &= ~(1 << (c - 1));
+			return;
+		}
+		acc_ramp->barred_t3 &= ~(1 << (c - 1));
+	}
+
+	/* If we have not allowed all ACCs yet, schedule another ramping step. */
+	if (acc_ramp_get_barred_t2(acc_ramp) != 0x00 ||
+	    acc_ramp_get_barred_t3(acc_ramp) != 0x00)
+		osmo_timer_schedule(&acc_ramp->step_timer, get_next_step_interval(acc_ramp), 0);
+}
+
+void acc_ramp_init(struct acc_ramp *acc_ramp, struct gsm_bts *bts)
+{
+	acc_ramp->bts = bts;
+	allow_all_accs(acc_ramp);
 	acc_ramp->step_size = ACC_RAMP_STEP_SIZE_DEFAULT;
 	acc_ramp->step_interval_sec = ACC_RAMP_STEP_INTERVAL_DEFAULT;
 	acc_ramp->step_interval_is_fixed = false;
-	osmo_timer_setup(&acc_ramp->step_timer, acc_ramp_timer_step, acc_ramp);
+	osmo_timer_setup(&acc_ramp->step_timer, acc_ramping_step, acc_ramp);
+}
+
+int acc_ramp_set_step_size(struct acc_ramp *acc_ramp, enum acc_ramp_step_size step_size)
+{
+	if (step_size < ACC_RAMP_STEP_SIZE_MIN || step_size > ACC_RAMP_STEP_SIZE_MAX)
+		return -ERANGE;
+
+	acc_ramp->step_size = step_size;
+	return 0;
+}
+
+int acc_ramp_set_step_interval(struct acc_ramp *acc_ramp, unsigned int step_interval)
+{
+	if (step_interval < ACC_RAMP_STEP_INTERVAL_MIN || step_interval > ACC_RAMP_STEP_INTERVAL_MAX)
+		return -ERANGE;
+
+	acc_ramp->step_interval_sec = step_interval;
+	acc_ramp->step_interval_is_fixed = true;
+	return 0;
+}
+
+void acc_ramp_set_step_interval_dynamic(struct acc_ramp *acc_ramp)
+{
+	acc_ramp->step_interval_is_fixed = false;
 }
 
 void acc_ramp_start(struct acc_ramp *acc_ramp)
 {
-	acc_ramp_stop(acc_ramp);
-	osmo_timer_schedule(&acc_ramp->step_timer, acc_ramp->step_interval_sec, 0);
+	/* Abort any previously running ramping process. */
+	acc_ramp_abort(acc_ramp);
+
+	/* Set all ACCs to denied and start ramping up. */
+	deny_all_accs(acc_ramp);
+	acc_ramping_step(acc_ramp);
 }
 
-void acc_ramp_stop(struct acc_ramp *acc_ramp)
+void acc_ramp_abort(struct acc_ramp *acc_ramp)
 {
 	if (osmo_timer_pending(&acc_ramp->step_timer))
 		osmo_timer_del(&acc_ramp->step_timer);
diff --git a/src/libcommon/gsm_data.c b/src/libcommon/gsm_data.c
index 443481b54..7774c3b2e 100644
--- a/src/libcommon/gsm_data.c
+++ b/src/libcommon/gsm_data.c
@@ -261,7 +261,7 @@ struct gsm_bts *gsm_bts_alloc_register(struct gsm_network *net, enum gsm_bts_typ
 	bts->si_common.chan_desc.t3212 = net->t3212; /* Use network's current value */
 	gsm_bts_set_radio_link_timeout(bts, 32); /* Use RADIO LINK TIMEOUT of 32 */
 
-	acc_ramp_init(&bts->acc_ramp);
+	acc_ramp_init(&bts->acc_ramp, bts);
 
 	llist_add_tail(&bts->list, &net->bts_list);
 
diff --git a/src/libcommon/gsm_data_shared.c b/src/libcommon/gsm_data_shared.c
index 57bf77d06..246e7d79e 100644
--- a/src/libcommon/gsm_data_shared.c
+++ b/src/libcommon/gsm_data_shared.c
@@ -396,6 +396,8 @@ struct gsm_bts *gsm_bts_alloc(struct gsm_network *net, uint8_t bts_num)
 	/* timer overrides */
 	bts->T3122 = 0; /* not overriden by default */
 
+	bts->chan_load_avg = 0;
+
 	return bts;
 }