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diff --git a/src/time_cc.c b/src/time_cc.c
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+/*! \file foo.c
+ * Report the cumulative counter of time for which a flag is true as rate counter.
+ */
+/* Copyright (C) 2021 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ *
+ * All Rights Reserved
+ *
+ * Author: Neels Hofmeyr <nhofmeyr@sysmocom.de>
+ *
+ * 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/>.
+ *
+ */
+
+/*! \addtogroup time_cc
+ *
+ * Report the cumulative counter of time for which a flag is true as rate counter.
+ *
+ * Useful for reporting cumulative time counters as defined in 3GPP TS 52.402, for example allAvailableSDCCHAllocated,
+ * allAvailableTCHAllocated, availablePDCHAllocatedTime.
+ *
+ * For a usage example, see the description of struct osmo_time_cc.
+ *
+ * @{
+ * \file time_cc.c
+ */
+
+#include <limits.h>
+
+#include <osmocom/core/tdef.h>
+#include <osmocom/core/rate_ctr.h>
+#include <osmocom/core/time_cc.h>
+
+#define GRAN_USEC(TIME_CC) ((TIME_CC)->cfg.gran_usec ? : 1000000)
+#define ROUND_THRESHOLD_USEC(TIME_CC) ((TIME_CC)->cfg.round_threshold_usec ? \
+ OSMO_MIN((TIME_CC)->cfg.round_threshold_usec, GRAN_USEC(TIME_CC)) \
+ : (GRAN_USEC(TIME_CC) / 2))
+
+static uint64_t time_now_usec()
+{
+ struct timespec tp;
+ if (osmo_clock_gettime(CLOCK_MONOTONIC, &tp))
+ return 0;
+ return (uint64_t)tp.tv_sec * 1000000 + tp.tv_nsec / 1000;
+}
+
+static void osmo_time_cc_forget_sum(struct osmo_time_cc *tc, uint64_t now);
+
+static void osmo_time_cc_update_from_tdef(struct osmo_time_cc *tc, uint64_t now)
+{
+ bool do_forget_sum = false;
+ if (!tc->cfg.T_defs)
+ return;
+ if (tc->cfg.T_gran) {
+ uint64_t was = GRAN_USEC(tc);
+ tc->cfg.gran_usec = osmo_tdef_get(tc->cfg.T_defs, tc->cfg.T_gran, OSMO_TDEF_US, -1);
+ if (was != GRAN_USEC(tc))
+ do_forget_sum = true;
+ }
+ if (tc->cfg.T_round_threshold)
+ tc->cfg.round_threshold_usec = osmo_tdef_get(tc->cfg.T_defs, tc->cfg.T_round_threshold,
+ OSMO_TDEF_US, -1);
+ if (tc->cfg.T_forget_sum) {
+ uint64_t was = tc->cfg.forget_sum_usec;
+ tc->cfg.forget_sum_usec = osmo_tdef_get(tc->cfg.T_defs, tc->cfg.T_forget_sum, OSMO_TDEF_US, -1);
+ if (tc->cfg.forget_sum_usec && was != tc->cfg.forget_sum_usec)
+ do_forget_sum = true;
+ }
+
+ if (do_forget_sum && tc->sum)
+ osmo_time_cc_forget_sum(tc, now);
+}
+
+static void osmo_time_cc_schedule_timer(struct osmo_time_cc *tc, uint64_t now);
+
+/*! Clear out osmo_timer and internal counting state of struct osmo_time_cc. The .cfg remains unaffected. After calling,
+ * the osmo_time_cc instance can be used again to accumulate state as if it had just been initialized. */
+void osmo_time_cc_cleanup(struct osmo_time_cc *tc)
+{
+ osmo_timer_del(&tc->timer);
+ *tc = (struct osmo_time_cc){
+ .cfg = tc->cfg,
+ };
+}
+
+static void osmo_time_cc_start(struct osmo_time_cc *tc, uint64_t now)
+{
+ osmo_time_cc_cleanup(tc);
+ tc->start_time = now;
+ tc->last_counted_time = now;
+ osmo_time_cc_update_from_tdef(tc, now);
+ osmo_time_cc_schedule_timer(tc, now);
+}
+
+static void osmo_time_cc_count_time(struct osmo_time_cc *tc, uint64_t now)
+{
+ uint64_t time_delta = now - tc->last_counted_time;
+ tc->last_counted_time = now;
+ if (!tc->flag_state)
+ return;
+ /* Flag is currently true, cumulate the elapsed time */
+ tc->total_sum += time_delta;
+ tc->sum += time_delta;
+}
+
+static void osmo_time_cc_report(struct osmo_time_cc *tc, uint64_t now)
+{
+ uint64_t delta;
+ uint64_t n;
+ if (!tc->cfg.rate_ctr)
+ return;
+ /* We report a sum "rounded up", ahead of time. If the granularity period has not yet elapsed after the last
+ * reporting, do not report again yet. */
+ if (tc->reported_sum > tc->sum)
+ return;
+ delta = tc->sum - tc->reported_sum;
+ /* elapsed full periods */
+ n = delta / GRAN_USEC(tc);
+ /* If the delta has passed round_threshold (normally half of gran_usec), increment. */
+ delta -= n * GRAN_USEC(tc);
+ if (delta >= ROUND_THRESHOLD_USEC(tc))
+ n++;
+ if (!n)
+ return;
+
+ /* integer sanity, since rate_ctr_add() takes an int argument. */
+ if (n > INT_MAX)
+ n = INT_MAX;
+ rate_ctr_add(tc->cfg.rate_ctr, n);
+ /* Store the increments of gran_usec that were counted. */
+ tc->reported_sum += n * GRAN_USEC(tc);
+}
+
+static void osmo_time_cc_forget_sum(struct osmo_time_cc *tc, uint64_t now)
+{
+ tc->reported_sum = 0;
+ tc->sum = 0;
+
+ if (tc->last_counted_time < now)
+ tc->last_counted_time = now;
+}
+
+/*! Initialize struct osmo_time_cc. Call this once before use, and before setting up the .cfg items. */
+void osmo_time_cc_init(struct osmo_time_cc *tc)
+{
+ *tc = (struct osmo_time_cc){0};
+}
+
+/*! Report state to be recorded by osmo_time_cc instance. Setting an unchanged state repeatedly has no effect. */
+void osmo_time_cc_set_flag(struct osmo_time_cc *tc, bool flag)
+{
+ uint64_t now = time_now_usec();
+ if (!tc->start_time)
+ osmo_time_cc_start(tc, now);
+ /* No flag change == no effect */
+ if (flag == tc->flag_state)
+ return;
+ /* Sum up elapsed time, report increments for that. */
+ osmo_time_cc_count_time(tc, now);
+ osmo_time_cc_report(tc, now);
+ tc->flag_state = flag;
+ osmo_time_cc_schedule_timer(tc, now);
+}
+
+static void osmo_time_cc_timer_cb(void *data)
+{
+ struct osmo_time_cc *tc = data;
+ uint64_t now = time_now_usec();
+
+ osmo_time_cc_update_from_tdef(tc, now);
+
+ if (tc->flag_state) {
+ osmo_time_cc_count_time(tc, now);
+ osmo_time_cc_report(tc, now);
+ } else if (tc->cfg.forget_sum_usec && tc->sum
+ && (now >= tc->last_counted_time + tc->cfg.forget_sum_usec)) {
+ osmo_time_cc_forget_sum(tc, now);
+ }
+ osmo_time_cc_schedule_timer(tc, now);
+}
+
+/*! Figure out the next time we should do anything, if the flag state remains unchanged. */
+static void osmo_time_cc_schedule_timer(struct osmo_time_cc *tc, uint64_t now)
+{
+ uint64_t next_event = UINT64_MAX;
+
+ osmo_time_cc_update_from_tdef(tc, now);
+
+ /* If it is required, when will the next forget_sum happen? */
+ if (tc->cfg.forget_sum_usec && !tc->flag_state && tc->sum > 0) {
+ uint64_t next_forget_time = tc->last_counted_time + tc->cfg.forget_sum_usec;
+ next_event = OSMO_MIN(next_event, next_forget_time);
+ }
+ /* Next rate_ctr increment? */
+ if (tc->flag_state && tc->cfg.rate_ctr) {
+ uint64_t next_inc = now + (tc->reported_sum - tc->sum) + ROUND_THRESHOLD_USEC(tc);
+ next_event = OSMO_MIN(next_event, next_inc);
+ }
+
+ /* No event coming up? */
+ if (next_event == UINT64_MAX)
+ return;
+
+ if (next_event <= now)
+ next_event = 0;
+ else
+ next_event -= now;
+
+ osmo_timer_setup(&tc->timer, osmo_time_cc_timer_cb, tc);
+ osmo_timer_del(&tc->timer);
+ osmo_timer_schedule(&tc->timer, next_event / 1000000, next_event % 1000000);
+}
+
+/*! @} */