osd-contiki/core/net/mac/tsch/tsch-adaptive-timesync.c

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2015-11-11 17:34:33 +01:00
/*
* Copyright (c) 2015, SICS Swedish ICT.
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. Neither the name of the Institute nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* This file is part of the Contiki operating system.
*
*/
/**
* \file
* TSCH adaptive time synchronization
* \author
* Atis Elsts <atis.elsts@sics.se>
*
*/
#include "tsch-adaptive-timesync.h"
#include "tsch-log.h"
#include <stdio.h>
#if TSCH_ADAPTIVE_TIMESYNC
/* Estimated drift of the time-source neighbor. Can be negative.
* Units used: ppm multiplied by 256. */
static int32_t drift_ppm;
/* Ticks compensated locally since the last timesync time */
static int32_t compensated_ticks;
/* Number of already recorded timesync history entries */
static uint8_t timesync_entry_count;
/* Since last learning of the drift; may be more than time since last timesync */
static uint32_t asn_since_last_learning;
/* Units in which drift is stored: ppm * 256 */
#define TSCH_DRIFT_UNIT (1000L * 1000 * 256)
/*---------------------------------------------------------------------------*/
/* Add a value to a moving average estimator */
static int32_t
timesync_entry_add(int32_t val, uint32_t time_delta)
{
#define NUM_TIMESYNC_ENTRIES 8
static int32_t buffer[NUM_TIMESYNC_ENTRIES];
static uint8_t pos;
int i;
if(timesync_entry_count == 0) {
pos = 0;
}
buffer[pos] = val;
if(timesync_entry_count < NUM_TIMESYNC_ENTRIES) {
timesync_entry_count++;
}
pos = (pos + 1) % NUM_TIMESYNC_ENTRIES;
val = 0;
for(i = 0; i < timesync_entry_count; ++i) {
val += buffer[i];
}
return val / timesync_entry_count;
}
/*---------------------------------------------------------------------------*/
/* Learn the neighbor drift rate at ppm */
static void
timesync_learn_drift_ticks(uint32_t time_delta_asn, int32_t drift_ticks)
{
/* should fit in 32-bit unsigned integer */
uint32_t time_delta_ticks = time_delta_asn * tsch_timing[tsch_ts_timeslot_length];
int32_t real_drift_ticks = drift_ticks + compensated_ticks;
int32_t last_drift_ppm = (int32_t)((int64_t)real_drift_ticks * TSCH_DRIFT_UNIT / time_delta_ticks);
drift_ppm = timesync_entry_add(last_drift_ppm, time_delta_ticks);
}
/*---------------------------------------------------------------------------*/
/* Either reset or update the neighbor's drift */
void
tsch_timesync_update(struct tsch_neighbor *n, uint16_t time_delta_asn, int32_t drift_correction)
{
/* Account the drift if either this is a new timesource,
* or the timedelta is not too small, as smaller timedelta
* means proportionally larger measurement error. */
if(last_timesource_neighbor != n) {
last_timesource_neighbor = n;
drift_ppm = 0;
timesync_entry_count = 0;
compensated_ticks = 0;
asn_since_last_learning = 0;
} else {
asn_since_last_learning += time_delta_asn;
if(asn_since_last_learning >= 4 * TSCH_SLOTS_PER_SECOND) {
timesync_learn_drift_ticks(asn_since_last_learning, drift_correction);
compensated_ticks = 0;
asn_since_last_learning = 0;
} else {
/* Too small timedelta, do not recalculate the drift to avoid introducing error. instead account for the corrected ticks */
compensated_ticks += drift_correction;
}
}
}
/*---------------------------------------------------------------------------*/
/* Error-accumulation free compensation algorithm */
static int32_t
compensate_internal(uint32_t time_delta_usec, int32_t drift_ppm, int32_t *remainder, int16_t *tick_conversion_error)
{
int64_t d = (int64_t)time_delta_usec * drift_ppm + *remainder;
int32_t amount = d / TSCH_DRIFT_UNIT;
int32_t amount_ticks;
*remainder = (int32_t)(d - amount * TSCH_DRIFT_UNIT);
amount += *tick_conversion_error;
amount_ticks = US_TO_RTIMERTICKS(amount);
*tick_conversion_error = amount - RTIMERTICKS_TO_US(amount_ticks);
if(ABS(amount_ticks) > RTIMER_ARCH_SECOND / 128) {
TSCH_LOG_ADD(tsch_log_message,
snprintf(log->message, sizeof(log->message),
"!too big compensation %ld delta %ld", amount_ticks, time_delta_usec));
amount_ticks = (amount_ticks > 0 ? RTIMER_ARCH_SECOND : -RTIMER_ARCH_SECOND) / 128;
}
return amount_ticks;
}
/*---------------------------------------------------------------------------*/
/* Do the compensation step before scheduling a new timeslot */
int32_t
tsch_timesync_adaptive_compensate(rtimer_clock_t time_delta_ticks)
{
int32_t result = 0;
uint32_t time_delta_usec = RTIMERTICKS_TO_US_64(time_delta_ticks);
/* compensate, but not if the neighbor is not known */
if(drift_ppm && last_timesource_neighbor != NULL) {
static int32_t remainder;
static int16_t tick_conversion_error;
result = compensate_internal(time_delta_usec, drift_ppm,
&remainder, &tick_conversion_error);
compensated_ticks += result;
}
if(TSCH_BASE_DRIFT_PPM) {
static int32_t base_drift_remainder;
static int16_t base_drift_tick_conversion_error;
result += compensate_internal(time_delta_usec, 256L * TSCH_BASE_DRIFT_PPM,
&base_drift_remainder, &base_drift_tick_conversion_error);
}
return result;
}
/*---------------------------------------------------------------------------*/
#else /* TSCH_ADAPTIVE_TIMESYNC */
/*---------------------------------------------------------------------------*/
void
tsch_timesync_update(struct tsch_neighbor *n, uint16_t time_delta_asn, int32_t drift_correction)
{
}
/*---------------------------------------------------------------------------*/
int32_t
tsch_timesync_adaptive_compensate(rtimer_clock_t delta_ticks)
{
return 0;
}
/*---------------------------------------------------------------------------*/
#endif /* TSCH_ADAPTIVE_TIMESYNC */