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Adaptive time synchronization for TSCH

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Atis Elsts 2015-11-11 17:34:33 +01:00 committed by Simon Duquennoy
parent f9f91363d2
commit d79ce957a1
9 changed files with 327 additions and 26 deletions
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6
apps/orchestra/orchestra-conf.h
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@ -98,8 +98,8 @@
/* Is the "hash" function collision-free? (e.g. it maps to unique node-ids) */
#ifdef ORCHESTRA_CONF_COLLISION_FREE_HASH
#define ORCHESTRA_COLLISION_FREE_HASH ORCHESTRA_CONF_COLLISION_FREE_HASH
#else /* ORCHESTRA_CONF_MAX_HASH */
#define ORCHESTRA_CONF_COLLISION_FREE_HASH 0 /* Set to 1 if ORCHESTRA_LINKADDR_HASH returns unique hashes */
#endif /* ORCHESTRA_CONF_MAX_HASH */
#else /* ORCHESTRA_CONF_COLLISION_FREE_HASH */
#define ORCHESTRA_COLLISION_FREE_HASH 0 /* Set to 1 if ORCHESTRA_LINKADDR_HASH returns unique hashes */
#endif /* ORCHESTRA_CONF_COLLISION_FREE_HASH */
#endif /* __ORCHESTRA_CONF_H__ */

2
core/net/mac/tsch/Makefile.tsch
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@ -1 +1 @@
CONTIKI_SOURCEFILES += tsch.c tsch-slot-operation.c tsch-queue.c tsch-packet.c tsch-schedule.c tsch-log.c tsch-rpl.c
CONTIKI_SOURCEFILES += tsch.c tsch-slot-operation.c tsch-queue.c tsch-packet.c tsch-schedule.c tsch-log.c tsch-rpl.c tsch-adaptive-timesync.c

186
core/net/mac/tsch/tsch-adaptive-timesync.c Normal file
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@ -0,0 +1,186 @@
/*
* 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 */

89
core/net/mac/tsch/tsch-adaptive-timesync.h Normal file
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@ -0,0 +1,89 @@
/*
* 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.
*
*/
#ifndef __TSCH_ADAPTIVE_TIMESYNC_H__
#define __TSCH_ADAPTIVE_TIMESYNC_H__
/********** Includes **********/
#include "contiki.h"
#include "net/mac/tsch/tsch-private.h"
/******** Configuration *******/
/* Use SFD timestamp for synchronization? By default we merely rely on rtimer and busy wait
* until SFD is high, which we found to provide greater accuracy on JN516x and CC2420.
* Note: for association, however, we always use SFD timestamp to know the time of arrival
* of the EB (because we do not busy-wait for the whole scanning process)
* */
#ifdef TSCH_CONF_RESYNC_WITH_SFD_TIMESTAMPS
#define TSCH_RESYNC_WITH_SFD_TIMESTAMPS TSCH_CONF_RESYNC_WITH_SFD_TIMESTAMPS
#else
#define TSCH_RESYNC_WITH_SFD_TIMESTAMPS 0
#endif
/* If enabled, remove jitter due to measurement errors */
#ifdef TSCH_CONF_TIMESYNC_REMOVE_JITTER
#define TSCH_TIMESYNC_REMOVE_JITTER TSCH_CONF_TIMESYNC_REMOVE_JITTER
#else
#define TSCH_TIMESYNC_REMOVE_JITTER TSCH_RESYNC_WITH_SFD_TIMESTAMPS
#endif
/* The jitter to remove in ticks.
* This should be the sum of measurement errors on Tx and Rx nodes.
* */
#define TSCH_TIMESYNC_MEASUREMENT_ERROR US_TO_RTIMERTICKS(32)
/* Base drift value.
* Used to compensate locally know inaccuracies, such as
* the effect of having a binary 32.768 kHz timer as the TSCH time base. */
#ifdef TSCH_CONF_BASE_DRIFT_PPM
#define TSCH_BASE_DRIFT_PPM TSCH_CONF_BASE_DRIFT_PPM
#else
#define TSCH_BASE_DRIFT_PPM 0
#endif
/* The approximate number of slots per second */
#define TSCH_SLOTS_PER_SECOND (1000000 / TSCH_DEFAULT_TS_TIMESLOT_LENGTH)
/***** External Variables *****/
/* The neighbor last used as our time source */
extern struct tsch_neighbor *last_timesource_neighbor;
/********** Functions *********/
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);
#endif /* __TSCH_ADAPTIVE_TIMESYNC_H__ */

7
core/net/mac/tsch/tsch-conf.h
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@ -168,4 +168,11 @@
#define TSCH_WITH_LINK_SELECTOR 0
#endif /* TSCH_CONF_WITH_LINK_SELECTOR */
/* Estimate the drift of the time-source neighbor and compensate for it? */
#ifdef TSCH_CONF_ADAPTIVE_TIMESYNC
#define TSCH_ADAPTIVE_TIMESYNC TSCH_CONF_ADAPTIVE_TIMESYNC
#else
#define TSCH_ADAPTIVE_TIMESYNC 0
#endif
#endif /* __TSCH_CONF_H__ */

48
core/net/mac/tsch/tsch-slot-operation.c
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@ -52,6 +52,7 @@
#include "net/mac/tsch/tsch-log.h"
#include "net/mac/tsch/tsch-packet.h"
#include "net/mac/tsch/tsch-security.h"
#include "net/mac/tsch/tsch-adaptive-timesync.h"
#if TSCH_LOG_LEVEL >= 1
#define DEBUG DEBUG_PRINT
@ -126,9 +127,13 @@ static volatile int tsch_locked = 0;
static volatile int tsch_lock_requested = 0;
/* Last estimated drift in RTIMER ticks
* (Sky: 1 tick ~= 30.52 uSec) */
* (Sky: 1 tick = 30.517578125 usec exactly) */
static int32_t drift_correction = 0;
static struct tsch_neighbor *drift_neighbor = NULL;
/* Is drift correction used? (Can be true even if drift_correction == 0) */
static uint8_t is_drift_correction_used;
/* The neighbor last used as our time source */
struct tsch_neighbor *last_timesource_neighbor = NULL;
/* Used from tsch_slot_operation and sub-protothreads */
static rtimer_clock_t volatile current_slot_start;
@ -545,6 +550,7 @@ PT_THREAD(tsch_tx_slot(struct pt *pt, struct rtimer *t))
if(ack_len != 0) {
if(is_time_source) {
int32_t eack_time_correction = US_TO_RTIMERTICKS(ack_ies.ie_time_correction);
int32_t since_last_timesync = ASN_DIFF(current_asn, last_sync_asn);
if(eack_time_correction > SYNC_IE_BOUND) {
drift_correction = SYNC_IE_BOUND;
} else if(eack_time_correction < -SYNC_IE_BOUND) {
@ -558,7 +564,8 @@ PT_THREAD(tsch_tx_slot(struct pt *pt, struct rtimer *t))
"!truncated dr %d %d", (int)eack_time_correction, (int)drift_correction);
);
}
drift_neighbor = current_neighbor;
is_drift_correction_used = 1;
tsch_timesync_update(current_neighbor, since_last_timesync, drift_correction);
/* Keep track of sync time */
last_sync_asn = current_asn;
tsch_schedule_keepalive();
@ -595,7 +602,7 @@ PT_THREAD(tsch_tx_slot(struct pt *pt, struct rtimer *t))
log->tx.num_tx = current_packet->transmissions;
log->tx.datalen = queuebuf_datalen(current_packet->qb);
log->tx.drift = drift_correction;
log->tx.drift_used = drift_neighbor != NULL;
log->tx.drift_used = is_drift_correction_used;
log->tx.is_data = ((((uint8_t *)(queuebuf_dataptr(current_packet->qb)))[0]) & 7) == FRAME802154_DATAFRAME;
log->tx.sec_level = queuebuf_attr(current_packet->qb, PACKETBUF_ATTR_SECURITY_LEVEL);
log->tx.dest = TSCH_LOG_ID_FROM_LINKADDR(queuebuf_addr(current_packet->qb, PACKETBUF_ADDR_RECEIVER));
@ -643,6 +650,7 @@ PT_THREAD(tsch_rx_slot(struct pt *pt, struct rtimer *t))
static rtimer_clock_t rx_start_time;
static rtimer_clock_t expected_rx_time;
static rtimer_clock_t packet_duration;
uint8_t packet_seen;
expected_rx_time = current_slot_start + tsch_timing[tsch_ts_tx_offset];
/* Default start time: expected Rx time */
@ -656,13 +664,16 @@ PT_THREAD(tsch_rx_slot(struct pt *pt, struct rtimer *t))
/* Start radio for at least guard time */
NETSTACK_RADIO.on();
if(!NETSTACK_RADIO.receiving_packet()) {
packet_seen = NETSTACK_RADIO.receiving_packet();
if(!packet_seen) {
/* Check if receiving within guard time */
BUSYWAIT_UNTIL_ABS(NETSTACK_RADIO.receiving_packet(),
BUSYWAIT_UNTIL_ABS((packet_seen = NETSTACK_RADIO.receiving_packet()),
current_slot_start, tsch_timing[tsch_ts_rx_offset] + tsch_timing[tsch_ts_rx_wait]);
}
if(packet_seen) {
TSCH_DEBUG_RX_EVENT();
/* Save packet timestamp */
rx_start_time = RTIMER_NOW();
rx_start_time = RTIMER_NOW() - RADIO_DELAY_BEFORE_DETECT;
}
if(!NETSTACK_RADIO.receiving_packet() && !NETSTACK_RADIO.pending_packet()) {
NETSTACK_RADIO.off();
@ -724,6 +735,17 @@ PT_THREAD(tsch_rx_slot(struct pt *pt, struct rtimer *t))
int do_nack = 0;
estimated_drift = ((int32_t)expected_rx_time - (int32_t)rx_start_time);
#if TSCH_TIMESYNC_REMOVE_JITTER
/* remove jitter due to measurement errors */
if(abs(estimated_drift) <= TSCH_TIMESYNC_MEASUREMENT_ERROR) {
estimated_drift = 0;
} else if(estimated_drift > 0) {
estimated_drift -= TSCH_TIMESYNC_MEASUREMENT_ERROR;
} else {
estimated_drift += TSCH_TIMESYNC_MEASUREMENT_ERROR;
}
#endif
#ifdef TSCH_CALLBACK_DO_NACK
if(frame.fcf.ack_required) {
do_nack = TSCH_CALLBACK_DO_NACK(current_link,
@ -759,11 +781,13 @@ PT_THREAD(tsch_rx_slot(struct pt *pt, struct rtimer *t))
/* If the sender is a time source, proceed to clock drift compensation */
n = tsch_queue_get_nbr(&source_address);
if(n != NULL && n->is_time_source) {
int32_t since_last_timesync = ASN_DIFF(current_asn, last_sync_asn);
/* Keep track of last sync time */
last_sync_asn = current_asn;
/* Save estimated drift */
drift_correction = -estimated_drift;
drift_neighbor = n;
is_drift_correction_used = 1;
tsch_timesync_update(n, since_last_timesync, -estimated_drift);
tsch_schedule_keepalive();
}
@ -776,7 +800,7 @@ PT_THREAD(tsch_rx_slot(struct pt *pt, struct rtimer *t))
log->rx.is_unicast = frame.fcf.ack_required;
log->rx.datalen = current_input->len;
log->rx.drift = drift_correction;
log->rx.drift_used = drift_neighbor != NULL;
log->rx.drift_used = is_drift_correction_used;
log->rx.is_data = frame.fcf.frame_type == FRAME802154_DATAFRAME;
log->rx.sec_level = frame.aux_hdr.security_control.security_level;
log->rx.estimated_drift = estimated_drift;
@ -849,7 +873,7 @@ PT_THREAD(tsch_slot_operation(struct rtimer *t, void *ptr))
NETSTACK_RADIO.set_value(RADIO_PARAM_CHANNEL, current_channel);
/* Reset drift correction */
drift_correction = 0;
drift_neighbor = NULL;
is_drift_correction_used = 0;
/* Decide whether it is a TX/RX/IDLE or OFF slot */
/* Actual slot operation */
if(current_packet != NULL) {
@ -878,6 +902,7 @@ PT_THREAD(tsch_slot_operation(struct rtimer *t, void *ptr))
"! leaving the network, last sync %u",
(unsigned)ASN_DIFF(current_asn, last_sync_asn));
);
last_timesource_neighbor = NULL;
tsch_disassociate();
} else {
/* backup of drift correction for printing debug messages */
@ -908,10 +933,11 @@ PT_THREAD(tsch_slot_operation(struct rtimer *t, void *ptr))
/* Time to next wake up */
time_to_next_active_slot = timeslot_diff * tsch_timing[tsch_ts_timeslot_length] + drift_correction;
drift_correction = 0;
drift_neighbor = NULL;
is_drift_correction_used = 0;
/* Update current slot start */
prev_slot_start = current_slot_start;
current_slot_start += time_to_next_active_slot;
current_slot_start += tsch_timesync_adaptive_compensate(time_to_next_active_slot);
} while(!tsch_schedule_slot_operation(t, prev_slot_start, time_to_next_active_slot, "main"));
}

11
core/net/mac/tsch/tsch-slot-operation.h
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@ -74,17 +74,6 @@
#define TSCH_MAX_INCOMING_PACKETS 4
#endif
/* Use SFD timestamp for synchronization? By default we merely rely on rtimer and busy wait
* until SFD is high, which we found to provide greater accuracy on JN516x and CC2420.
* Note: for association, however, we always use SFD timestamp to know the time of arrival
* of the EB (because we do not busy-wait for the whole scanning process)
* */
#ifdef TSCH_CONF_RESYNC_WITH_SFD_TIMESTAMPS
#define TSCH_RESYNC_WITH_SFD_TIMESTAMPS TSCH_CONF_RESYNC_WITH_SFD_TIMESTAMPS
#else
#define TSCH_RESYNC_WITH_SFD_TIMESTAMPS 0
#endif
/*********** Callbacks *********/
/* Called by TSCH form interrupt after receiving a frame, enabled upper-layer to decide

2
platform/sky/platform-conf.h
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@ -52,6 +52,8 @@
/* Delay between GO signal and start listening
* ~50us delay + 129preample + ?? = 183 us */
#define RADIO_DELAY_BEFORE_RX ((unsigned)US_TO_RTIMERTICKS(183))
/* Delay between the SFD finishes arriving and it is detected in software */
#define RADIO_DELAY_BEFORE_DETECT 0
#define PLATFORM_HAS_LEDS 1
#define PLATFORM_HAS_BUTTON 1

2
platform/z1/platform-conf.h
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@ -49,6 +49,8 @@
/* Delay between GO signal and start listening
* ~50us delay + 129preample + ?? = 183 us */
#define RADIO_DELAY_BEFORE_RX ((unsigned)US_TO_RTIMERTICKS(183))
/* Delay between the SFD finishes arriving and it is detected in software */
#define RADIO_DELAY_BEFORE_DETECT 0
#define PLATFORM_HAS_LEDS 1
#define PLATFORM_HAS_BUTTON 1