I have an OLD GPS receiver, and need to force it past the last gps 10 bit week rollover

fakegps

#!/usr/bin/env python3
# /opt/fakegps

"""
TL;DR: I have an OLD GPS receiver, and need to force it past the last gps 10 bit week rollover

TEST OUTPUT SITE: http://freenmea.net/decoder
WHY THIS IS A PROBLEM: https://gpsd.gitlab.io/gpsd/hacking.html#y2k1
INFO: https://github.com/rnorris/gpsd/blob/master/www/gpsd-time-service-howto.txt
MAN PAGE: http://manpages.ubuntu.com/manpages/trusty/man8/gpsd.8.html
PI HINTS: https://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html
PI HINTS: http://www.unixwiz.net/techtips/raspberry-pi3-gps-time.html
NMEA docs: http://aprs.gids.nl/nmea/#refs
HELPFUL COMMANDS:
gpsd -N -F /var/run/gpsd.sock -b -n -S 9999 /tmp/ttyGPS0.fifo
vi /etc/defaults/gpsd
cgps -s -l s <localhost:9999>
systemctl <cmd> gpsd | ntp
ntpq -p
vi /etc/ntp.conf
"""

import datetime
import os
import errno
import time


def modify(fifo, stream):
    for line in stream:
        if not line.startswith(b'$GPRMC'):
            fifo.write(line)
            fifo.flush()
            continue

        parts = line.split(b',')

        # Update DATE to account for 10 bit week counter
        d = parts[9]
        day, mon, yer = int(d[0:2]), int(d[2:4]), int(d[4:6])
        n = datetime.datetime(yer+2000, mon, day)
        n += datetime.timedelta(days=7*1024)
        parts[9] = n.strftime('%d%m%y').encode()

        # recompute checksum (xor all bytes between $ and *, print in hex)
        line = b','.join(parts)
        line = line[1:] # crop off the $
        line = line[:line.index(b'*')]
        n = 0
        for a in line:
            n ^= a
        chksum = hex(n)[2:].upper().encode()  # remove 0x
        fifo.write(b'$' + line + b'*' + chksum + b'\n')
        fifo.flush()


# Create a fifo file (ignore if it's already created)
path = '/tmp/ttyGPS0.fifo'
try:
    os.mkfifo(path)
    print('made /vmp/ttyGPS0.fifo')
except OSError as oe:
    if oe.errno != errno.EEXIST:
        raise
    print('/tmp/ttyGPS0.fifo already exists')

# Startup gpsd.
os.system('systemctl start gpsd')

# Continually listen for pipe readers and start transaction
while True:

    # spinloop for gpsd status (multiple readers not allowed)
    while os.system('pidof gpsd > /dev/null'):
        time.sleep(1)

    fifo = open(path, 'wb', 0)
    print("Connected")
    try:
        with open('/dev/ttyUSB0', 'rb', 1) as stream:
            modify(fifo, stream)
    except BrokenPipeError:
        print("Disconnected")
        fifo.close()

gpsd

# /etc/default/gpsd

START_DAEMON="true"
USBAUTO="false"
DEVICES="/tmp/ttyGPS0.fifo"

# -n don't wait for client to connect; poll GPS immediately
# -b bluetooth safe (try opening read only)
GPSD_OPTIONS="-n -b"

ntp.conf

# /etc/ntp.conf

# ... ommitted defaults ...

# interval of 5 == 32 seconds between updates == hot ARP cache (default is 6, or 64s, ARP cache default is 60s)
pool us.pool.ntp.org iburst minpoll 5 maxpoll 5

# GPS Data
server 127.127.28.0 minpoll 4 maxpoll 4 prefer
fudge 127.127.28.0 time1 -0.220 refid GPS

rc.local

#!/bin/sh -e
# /etc/rc.local

# Start fakegps (yes, there are more modern ways of doing this)
/opt/fakegps &

exit 0