187 lines
6.9 KiB
C
187 lines
6.9 KiB
C
/*
|
|
* 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 */
|