Table of Contents

Operating environment

Things you may need to buy

GlobalSat MR-350PS4 PS/2 pin-out

DB9 RS232 serial port pin-out

DB9 D-SUB RS232 Adapter (Female with Screw) screw pins

NTP time with GPSD and PPS-enabled GPS Garmin 18x LVC GPS

Comparison with the GlobalSat MR-250P-S4:

Package installation

Package versions

Assumptions

Configure GPSD

Enable kernel PPS

Check kernel config

CONFIG_PPS=mCONFIG_PPS_CLIENT_LDISC=m

Enable loading of pps_ldisc modules on boot

Configure serial port

Disable systemd-timesyncd.service

Setup chrony

Testing

Stop gpsd (systemd variant)

Restart gpsd (systemd variant)

Run gpsd in foreground for testing

Find pps device

pps0: name=serial1 path=/dev/ttyS1

Testing PPS capabilities

trying PPS source "/dev/pps0"found PPS source "/dev/pps0"timestamp: 1577777203, sequence: 83886, offset:   1984timestamp: 1577777204, sequence: 83887, offset: -31306timestamp: 1577777205, sequence: 83888, offset:   5836timestamp: 1577777206, sequence: 83889, offset:   3027timestamp: 1577777207, sequence: 83890, offset: -24220timestamp: 1577777208, sequence: 83891, offset:   2041

Testing PPS with ntpshmmon

ntpshmmon version 1#      Name Seen@                Clock                Real                 L Precsample NTP2 1577776857.467580012 1577776856.999992825 1577776857.000000000 0 -30sample NTP2 1577776858.000449336 1577776857.999980312 1577776858.000000000 0 -30sample NTP2 1577776859.000728372 1577776858.999985236 1577776859.000000000 0 -30sample NTP2 1577776860.000141189 1577776859.999987295 1577776860.000000000 0 -30sample NTP2 1577776861.000665371 1577776861.000004892 1577776861.000000000 0 -30

Testing GPS NMEA

Showing chrony status

chronyc -m 'sources -v' tracking 'sourcestats -v'

Sample chrony output

210 Number of sources = 7  .-- Source mode  '^' = server, '=' = peer, '#' = local clock. / .- Source state '*' = current synced, '+' = combined , '-' = not combined,| /   '?' = unreachable, 'x' = time may be in error, '~' = time too variable.||                                                 .- xxxx [ yyyy ] +/- zzzz||      Reachability register (octal) -.           |  xxxx = adjusted offset,||      Log2(Polling interval) --.      |          |  yyyy = measured offset,||                                \     |          |  zzzz = estimated error.||                                 |    |           \MS Name/IP address         Stratum Poll Reach LastRx Last sample               ===============================================================================#* PPS                           0   4   377    18  +1318ns[+2225ns] +/-  502us^- 162.159.200.1                 3  10   377    56  +8603us[+8606us] +/-   46ms^- time4.google.com              1  10   377   983  +1242us[+1189us] +/-   24ms^- time-a-b.nist.gov             1  10   377   128  -2043us[-2039us] +/-   22ms^- gpstime.la-archdiocese.n>     2  10   377   32m   +848us[ +667us] +/-   41ms^- clock.fmt.he.net              1  10   377   209  -1836us[-1831us] +/- 4597us^- clock.sjc.he.net              1  10   377    39   -507us[ -507us] +/- 3927us210 Number of sources = 7                             .- Number of sample points in measurement set.                            /    .- Number of residual runs with same sign.                           |    /    .- Length of measurement set (time).                           |   |    /      .- Est. clock freq error (ppm).                           |   |   |      /           .- Est. error in freq.                           |   |   |     |           /         .- Est. offset.                           |   |   |     |          |          |   On the -.                           |   |   |     |          |          |   samples. \                           |   |   |     |          |          |             |Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev==============================================================================PPS                        13   8   194     +0.001      0.062    +13ns  2834ns162.159.200.1              10   8  155m     -0.431      0.820  +6442us  1354ustime4.google.com           14   7  223m     -0.400      0.509  -1817us  1802ustime-a-b.nist.gov          34  14  568m     -0.328      0.070  -1429us  1134usgpstime.la-archdiocese.n>  20  12  327m     -0.342      0.123   -691us   799usclock.fmt.he.net           17  10  276m     -0.429      0.198   -507us  1020usclock.sjc.he.net           13   5  224m     -0.407      0.115   -933us   419usReference ID    : 50505300 (PPS)Stratum         : 1Ref time (UTC)  : Tue Dec 31 01:59:17 2019System time     : 0.000000606 seconds fast of NTP timeLast offset     : +0.000000953 secondsRMS offset      : 0.000001683 secondsFrequency       : 25.250 ppm slowResidual freq   : +0.001 ppmSkew            : 0.068 ppmRoot delay      : 0.001000000 secondsRoot dispersion : 0.000021925 secondsUpdate interval : 16.0 secondsLeap status     : Normal

Links

Contents of files

File list

.├── etc│   ├── chrony│   │   └── chrony.conf│   ├── default│   │   └── gpsd│   └── systemd│       └── system│           └── pps_ldisc.service└── var    └── lib        └── setserial            └── autoserial.conf

etc/default/gpsd

# Default settings for gpsd.# Please do not edit this file directly - use `dpkg-reconfigure gpsd' to# change the options.START_DAEMON="true"GPSD_OPTIONS="-b -n -D1"DEVICES="/dev/ttyS1 /dev/pps0"USBAUTO="false"GPSD_SOCKET="/var/run/gpsd.sock"

etc/systemd/system/pps_ldisc.service

[Unit]Description=Modprobe pps_ldiscAfter=setserial.service[Service]Type=oneshotExecStart=/sbin/modprobe pps_coreExecStart=/sbin/modprobe pps_ldisc[Install]WantedBy=gpsd.service

var/lib/setserial/autoserial.conf

####AUTOSAVE-ONCE######AUTOSAVE-ONCE######AUTOSAVE##### If you want to configure this file by hand, use # dpkg-reconfigure setserial# and change the configuration mode of the file to MANUAL. If you do not do this, this file may be overwritten automatically the next time you upgrade the# package.## dpkg-reconfigure setserial   ...  set configuration mode to MANUAL# Added next line for ttyS1 for Garmin 18 LVC GPS# From: http://www.rjsystems.nl/en/2100-ntpd-garmin-gps-18-lvc-gpsd.php# Only needed to add 'low_latency' to default port configuration# Print out current port configuration:#   setserial -G /dev/ttyS1/dev/ttyS1 uart 16550A port 0x02f8 irq 3 baud_base 115200 spd_normal skip_test low_latency

etc/chrony/chrony.conf

# This the default chrony.conf file for the Debian chrony package.  After# editing this file use the command 'invoke-rc.d chrony restart' to make# your changes take effect.  John Hasler <jhasler@debian.org> 1998-2008# See www.pool.ntp.org for an explanation of these servers.  Please# consider joining the project if possible.  If you can't or don't want to# use these servers I suggest that you try your ISP's nameservers.  We mark# the servers 'offline' so that chronyd won't try to connect when the link# is down.  Scripts in /etc/ppp/ip-up.d and /etc/ppp/ip-down.d use chronyc# commands to switch it on when a dialup link comes up and off when it goes# down.  Code in /etc/init.d/chrony attempts to determine whether or not# the link is up at boot time and set the online status accordingly.  If# you have an always-on connection such as cable omit the 'offline'# directive and chronyd will default to online.## Note that if Chrony tries to go "online" and dns lookup of the servers# fails they will be discarded.  Thus under some circumstances it is # better to use IP numbers than host names.# ------------------------------------------------------------------------# Use a local GPS device and gpsd as Staratum 0 GPS source## Disable systemd-timesyncd.service - conflicts with chrony autostart !#   for op in stop disable mask; do systemctl $op systemd-timesyncd.service ; done### For Globalsat MR-350PS4 PPS GPS on SERIAL port# From https://wiki.alpinelinux.org/wiki/Chrony_and_GPSD# Commenting out NEMA and SOCK -:#   - NEMA is too inaccurate and chrony will not use anyway!#   - SOCK - does not seem to get any values !##refclock SHM 0  delay 0.5 refid NEMArefclock SHM 1 offset 0 delay 0.001 refid PPS#refclock SOCK /var/run/chrony.ttyS1.sock delay 0.0 refid SOCK# C(20180207) Setings for using USB non-PPS GPS device and GPSD# NEMA is too inaccurate and chrony will not use anyway!# Need to fiddle with offset (seconds) to make sure refclock is considered# watch the output of 'chronyc sources' to see 'Last Sample'## refclock SHM 0 offset 0.05 refid NMEAserver clock.fmt.he.net iburstserver clock.sjc.he.net iburstserver time.cloudflare.com iburstserver time.google.com iburstserver time.nist.govserver gpstime.la-archdiocese.net#server time1.google.com iburst#server time2.google.com iburst#server time3.google.com iburst#server time4.google.com iburst#pool 0.ubuntu.pool.ntp.org iburst#pool 2.debian.pool.ntp.org offline iburst# Specify IP address (interface) that chronyd CLIENT will bind to# The bindacqaddress directive sets the network interface to which# chronyd will bind its NTP client sockets# bindacqaddress 0.0.0.0# Allow other NTP clients in our zone to query time# allow 10.3/16# allow 10.30.0/24# (CHANGED): chronyd version 3.2 commandkey directive is no longer supported# This directive sets the key ID used for authenticating user commands via the# 'chronyc' program at run time.# commandkey 1# End of customized settings - EXCEPT lines labeled with (CHANGED)# ------------------------------------------------------------------------# Look here for the admin password needed for chronyc.  The initial# password is generated by a random process at install time.  You may# change it if you wish.keyfile /etc/chrony/chrony.keys# I moved the driftfile to /var/lib/chrony to comply with the Debian# filesystem standard.driftfile /var/lib/chrony/chrony.drift# Comment this line out to turn off logging.log tracking measurements statisticslogdir /var/log/chrony# Stop bad estimates upsetting machine clock.maxupdateskew 100.0# Dump measurements when daemon exits.dumponexit# Specify directory for dumping measurements.dumpdir /var/lib/chrony# This directive lets 'chronyd' to serve time even if unsynchronised to any# NTP server.#local stratum 10# This directive designates subnets (or nodes) from which NTP clients are allowed# to access to 'chronyd'.#allow foo.example.net#allow 10/8#allow 0/0 (allow access by any IPv4 node)#allow ::/0 (allow access by any IPv6 node)# This directive forces `chronyd' to send a message to syslog if it# makes a system clock adjustment larger than a threshold value in seconds.logchange 0.5# This directive defines an email address to which mail should be sent# if chronyd applies a correction exceeding a particular threshold to the# system clock.# mailonchange root@localhost 0.5# This directive tells 'chronyd' to parse the 'adjtime' file to find out if the# real-time clock keeps local time or UTC. It overrides the 'rtconutc' directive.hwclockfile /etc/adjtime# This directive enables kernel synchronisation (every 11 minutes) of the# real-time clock. Note that it can’t be used along with the 'rtcfile' directive.rtcsync