sailtrack-timesync

#!/usr/bin/env python3

# `sailtrack-timesync` - Python script that continuously listens to the `sensor/gps0` topic for a message that
# contains the `epoch` field, setting the system time accordingly to the received epoch. This is needed because the
# Raspberry Pi has no RTC clock built-in and will therefore lose track of the time and date as soon as it is shut
# down. Instead, SailTrack Radio has a built-in RTC clock for the GPS, and therefore it sends, along with the GPS
# data, the current time and date.

import json
import logging
import os
import time
from datetime import timedelta

from paho.mqtt.client import Client, CallbackAPIVersion
from timeloop import Timeloop

# -------------------------- Configuration -------------------------- #

TIMESYNC_DELTA_THRESHOLD = 1
LOG_PRINT_FREQ_HZ = 0.1

MQTT_CLIENT_ID = "sailtrack-timesync"

LOG_JOB_INTERVAL_MS = 1000 / LOG_PRINT_FREQ_HZ

# ------------------------------------------------------------------- #

received_epochs = 0
time_syncs = 0
delta = 0


def on_message_callback(client, userdata, message):
    global received_epochs
    global time_syncs
    global delta
    doc = json.loads(message.payload)
    if "epoch" in doc and doc["epoch"]:
        received_epochs += 1
        delta = doc["epoch"] - int(time.time())
        if abs(delta) > TIMESYNC_DELTA_THRESHOLD:
            time.clock_settime(time.CLOCK_REALTIME, doc["epoch"])
            time_syncs += 1


mqtt = Client(CallbackAPIVersion.VERSION1, MQTT_CLIENT_ID)
mqtt.username_pw_set("mosquitto", os.environ["SAILTRACK_GLOBAL_PASSWORD"])
mqtt.on_message = on_message_callback
mqtt.connect("localhost")
mqtt.loop_start()
mqtt.subscribe("sensor/gps0")

tl = Timeloop()

formatter = logging.Formatter("[%(levelname)s] %(message)s")
logging.getLogger("timeloop").handlers[0].setFormatter(formatter)
logger = logging.getLogger(MQTT_CLIENT_ID)
logger.setLevel(logging.INFO)
handler = logging.StreamHandler()
handler.setFormatter(formatter)
logger.addHandler(handler)


@tl.job(interval=timedelta(milliseconds=LOG_JOB_INTERVAL_MS))
def log_job():
    logger.info(f"Received epochs: {received_epochs}, "
                f"Time syncs: {time_syncs}, "
                f"Delta: {delta}")


tl.start(block=True)