** About
This document was created by Steven Baltakatei Sandoval on
~2020-07-23T22:27Z~ under a [[https://creativecommons.org/licenses/by-sa/4.0/][Creative Commons BY-SA 4.0 license]]. It
-was updated by Steven Baltakatei Sandoval on ~2020-10-16T22:26Z~
+was updated by Steven Baltakatei Sandoval on ~2020-10-17T23:31Z~
** Narrative
The ~ninfacyzga-01~ device is equipped with an Ozzmaker BerryGPS-IMU
-module which provides time and location data to ~gpsd~ and ~ntpsec~. The
+module which provides time and location data to ~gpsd~ and ~chrony~. The
time is provided by GPS satellites which themselves are
equipped [fn:nasa_20020408_atomicclock] with atomic clocks. This
extremely accurate set of clocks are needed since a GPS receiver
*** Hardware
Ozzmaker BerryGPS-IMU, Version 3 (see [[https://ozzmaker.com/berrygps-berrygps-imu-quick-start-guide/][ref]]).
*** Software
+- [[https://www.raspberrypi.org/downloads/raspberry-pi-os/][Raspberry Pi OS]] : A GNU/Linux operating system derived from
+ Debian 10. This procedure was developed with version ~August 2020~.
+
- [[https://tracker.debian.org/pkg/gpsd][~gpsd~]] : A background daemon app capable of interfacing with the
[[https://ozzmaker.com/berrygps-berrygps-imu-quick-start-guide/][Ozzmaker BerryGPS-IMU]]'s GPS submodule. Installed and initialized by
~apt~. Should be installed along with the ~gpsd-clients~
package. This procedure was developed with ~gpsd~ version
-- [[https://tracker.debian.org/pkg/ntpsec][~ntpsec~]] : A security-hardned version of [[https://tracker.debian.org/pkg/ntp][~ntp~]] which is a "[[https://en.wikipedia.org/wiki/Network_Time_Protocol][Network
- Time Protocol]]" app that synchronizes the system clock with local or
- remote time servers or devices. It is capable of extracting time
- data from a GPS signal handled by ~gpsd~. It is also capable of
- using the high precision PPS (pulse-per-second) signal handled by
- ~gpsd~. Installed via ~apt~. This procedure was developed with
- ~ntpsec~ version ~1.1.3~.
+- [[https://chrony.tuxfamily.org/][~chrony~]] : A set of programs capable of continuously adjusting the
+ system clock until it is synchronized with configurable time sources
+ such as GPS and PPS data provided by ~gpsd~. ~chrony~ may be
+ configured to act as an NTP time client or server. It uses the same
+ protocol as ~ntp~ but is a GPLv2 implementation. This procedure was
+ developed with ~chrony~ version ~3.4-4~.
** Operating Procedures
*** Initial Startup
**** Install Software for time tracking
The time tracking function can be performed by two programs: ~gpsd~
-and ~ntpsec~.
+and ~chrony~.
Basically, two things need to happen:
incoming GPS data (in NMEA format) and the PPS signal ("pulse per
second"; a high precision time signal).
-2. ~ntpsec~ needs to be pointed towards the correct local IP addresses
+2. ~chrony~ needs to be pointed towards the correct local IP addresses
where ~gpsd~ provides GPS data and the PPS signal.
-~gpsd~ then will provide GPS and PPS data to ~ntpsec~ via a "shared
+~gpsd~ then will provide GPS and PPS data to ~chrony~ via a "shared
memory driver".
***** Install packages via ~apt~
Run the following command to install the required packages.
-: $ sudo apt install gpsd gpsd-clients python-gps pps-tools ntpsec
+: $ sudo apt install gpsd gpsd-clients python-gps pps-tools chrony
***** Enable PPS device
Modify the ~/boot/config.txt~ file in order to tell the Raspberry Pi
[[file:../setup/README.org][Main Setup]] Initial Startup procedure for instructions on how to
disable bluetooth to free up ~/dev/ttyAMA0~ for use by ~gpsd~.
-Note: Older ~ntp~ documentation indicates that ~ntp~ (and presumably
-~ntpsec~ might be able to access GPS data (ex: NMEA sentences) without
-the aid of ~gpsd~ itself if the data is available at a device named
-~/dev/ggp0~. Similarly, the same might apply to PPS data and the
-~/dev/gpspps0~ device. However, since the Raspberry Pi OS overlay
-system automatically creates ~/dev/pps0~ using the modifications to
-~/boot/config.txt~ (described [[*Enable PPS device][elsewhere]] in this procedure).
-
***** Setup ~gpsd~
See the "[[file:~/git-OC/ninfacyzga-01/doc/location/README.org::*Setup%20~gpsd~][Setup ~gpsd~]]" subsection within the "Initial Startup" section
of the Location Logging [[file:~/git-OC/ninfacyzga-01/doc/location/README.org][~README.org~]] file. There is one additional
GPSD_OPTIONS="-n"
#+END_EXAMPLE
-***** Setup ~ntpsec~
-The ~ntpsec~ configuration file at ~/etc/ntpsec/ntp.conf~ must be
-modified to tell ~ntpsec~ how to retrieve and interpret the GPS and
-PPS data provided by ~gpsd~.
+Make sure to enable ~gpsd~ to automatically start as a system service.
-In summary, lines need to be added telling ~ntpsec~ how often to poll
-certain sources (local or remote) for time information as well as how
-to prioritize and label information from each source.
+: $ sudo systemctl enable gpsd
+: $ sudo systemctl start gpsd
-~ntpsec~ uses syntax simplified from that of ~ntp~. Specifically, it
-recommends use of the ~refclock~ keyword for configuring local
-hardware clocks such as GPS and PPS devices.
+***** Setup ~chrony~
+Modify the configuration file for ~chrony~ at ~/etc/chrony/chrony.conf~.
-Below is an example of lines that may be added to
-~/etc/ntpsec/ntp.conf~ in order to ensure that the system clock will always have
+: $ sudo nano /etc/chrony/chrony.conf
+
+Add the following lines:
#+BEGIN_EXAMPLE
-# Local time sources
+# Get time from GPS (/dev/XXXX) and PPS (/dev/YYYY)
+#refclock SOCK /run/chrony.XXXX.sock refid GPS precision 1e-1 offset 0.0000
+#refclock SOCK /run/chrony.YYYY.sock refid PP precision 1e-7
+refclock SHM 0 refid GPS precision 1e-1 offset 0.0000 delay 0.2 stratum 1
+refclock SHM 1 refid PPS precision 1e-7 stratum 1
+#+END_EXAMPLE
-# Kernel PPS (precision seconds; driver 22)
-refclock pps unit 0 refid kPPS flag3 1 minpoll 4 maxpoll 4 stratum 1
+Where
+- ~XXXX~ : the basename of the GPS device's serial port. In this guide
+ it should be ~ttyAMA0~; other setups may use ~ttyS0~, ~ttyACM0~, or
+ ~serial0~.
-# GPS PPS reference (precision seconds; driver 28; root) (NTP1)
-refclock shm unit 1 refid PPS minpoll 4 maxpoll 4 iburst stratum 1
+- ~YYYY~ : the basename of the PPS device's serial port. In this guide
+ it should be ~pps0~.
-# GPS Serial data reference (coarse time; driver28; root) (NTP0)
-refclock shm unit 0 refid GPS prefer time1 0.109 minpoll 4 maxpoll 4 iburst stratum 1
+Note: The ~refclock SOCK~ lines are left as comments in case ~gpsd~
+incorrectly maps the GPS and PPS data.
-# GPS PPS reference (precision seconds; driver 28; user) (NTP2)
-refclock shm unit 2 refid PPSuser minpoll 4 maxpoll 4 iburst stratum 1
+The following commands may be useful for testing ~gpsd~ and ~chrony~
+configurations.
+- ~sudo chronyc sources -v~ : Shows time sources and associated accuracy
+ information.
-# Tolerate outliers (useful for coarse clocks)
-tos mindist 0.500
-#+END_EXAMPLE
+- ~sudo chronyc tracking~ : Shows the current time difference between
+ the reference clock and the system clock. Note: ~chrony~ gradually
+ attempts to reduce the difference by changing the system clock.
+
+- ~sudo chronyc makestep~ : Force ~chrony~ to set the system clock to
+ match the reference clock immediately.
+
+- ~sudo systemctl enable chrony~ : Enable automatic startup of
+ ~chrony~ (Note: This command shouldn't be necessary since the act of
+ installing ~chrony~ via ~sudo apt install chrony~ should
+ automatically enable it).
+
+- ~sudo systemctl stop chrony~ : Stop ~chrony~.
-A complete working example of an ~ntp.conf~ file is found in Appendix
-A of this document.
+- ~sudo systemctl restart chrony~ : Restart ~chrony~.
-Commands useful for examining the shared memory driver used by ~gpsd~
-and ~ntpsec~ are:
+- ~sudo systemctl status chrony~ : Check status of ~chrony~ service.
- ~sudo ntpshmmon~ : Shows live output of data using the shared memory
- driver. ([[https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html][ref]])
+ driver filled by ~gpsd~. ([[https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html][ref]])
- ~sudo ipcs -m~ : Show live segments of the shared memory. ([[https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html][ref]])
-General references for this configuration file are:
-
-- "Raspberry Pi as a Stratum-1 NTP Server - Updating to the final NTP
- configuration file" by David Taylor. [[http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html#ntp-conf][Link]]. Date: 2020-03-24. Note:
- An example of kernel PPS transfer from ~gpsd~ to ~ntp~ via
- ~127.127.22.0~.
-
-- "GPSD Time Service HOWTO" by Garry E. Miller. [[https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html][Link]]. Date:
- 2020-06-28. Note: Explains how shared memory segments available at
- ~127.127.28.0~, ~127.127.28.1~, ~127.127.28.2~, etc. work in context
- of an ~ntp~ configuration file.
-
-- "Building a Stratum 1 NTP Server with a Raspberry Pi 4 and Adafruit
- Ultimate GPS Hat". [[http://www.gregledet.net/computers/building-a-stratum-1-ntp-server-with-a-raspberry-pi-4-and-adafruit-ultimate-gps-hat/][Link]]. Date: 2020-02-23. Note: A concise example
- between ~gpsd~ and ~ntp~ setup for a Raspberry Pi 4 using
- ~127.127.28.0~ and ~127.127.28.1~. Recommends use of ~ntpsec~
- instead of ~ntp~.
-
-Expalantions of some ~ntpsec~ [[https://docs.ntpsec.org/latest/comdex.html][commands and options]] used in the
-configuration file include:
-
-- ~refclock~ : An ~ntpsec~ keyword not present in ~ntp-4.2.8~ that is
- meant to simplify configuration of reference clocks that use certain
- [[https://docs.ntpsec.org/latest/refclock.html][drivers]] including ~pps~ ([[https://docs.ntpsec.org/latest/driver_pps.html][PPS Clock Discipline]]), ~shm~ ([[https://docs.ntpsec.org/latest/driver_shm.html][Shared Memory
- Driver]]) . In ~ntp-4.2.8~ and earlier, in order to configure a clock,
- instead of ~ntpsec~'s one keyword (~refclock~), two keywords would
- be required (~server~ and ~fudge~).
-
-- ~server [address]~ : Tells ~ntpsec~ the address to query for time
- information. May be IP address or URL. Additional options such as
- ~minpoll~, ~maxpoll~, ~prefer~, and ~true~ may be added.
-
-- ~prefer~ : Indicates the source should be prioritized in some
- way. How exactly the ~ntpsec~ mitigation rules (see [[https://docs.ntpsec.org/latest/prefer.html][ref]]) use the
- ~prefer~ option is complicated but in the context of dealing with a
- GPS source and a PPS source, the GPS source should have a ~prefer~
- option. The PPS source may have a ~prefer~ option but it is not
- necessary; adding ~prefer~ to a PPS source is useful in the corner
- case that the GPS source is less reliable than another source (ex: a
- remote clock specified by ~server~).
-
-- ~... shm ... flag1 1~ : For an ~shm~ driver, tells ~ntpsec~ to
- ignore the default sanity check that discards any time that is more
- than 4-hours off from the system clock. Note that ~ntpsec~ treats
- ~shm flag1 1~ in the opposite manner as ~ntp~ (see [[https://docs.ntpsec.org/latest/driver_shm.html][ref]]).
-
-- ~... shm ... time1 [float]~ : Tells ~ntpsec~ that a latency
- time of ~[float]~ seconds is required for data to travel from the
- address to ~ntpsec~ (ex: a USB hub in the case of a GPS device that
- connects via USB). (see [[https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html#_feeding_ntpd_from_gpsd][ref]]) This number of seconds should be
- adjusted to reduce the `offset` time of the address indicated in the
- output of the ~ntpq -pn~ command to near ~0.000~. Note that the
- units of ~offset~ displayed by ~ntpq -pn~ are in milliseconds.
-
-- ~... refid [string]~ : Tells ~ntpsec~ a string used to label the source.
-
-- ~fudge~ : An ~ntp~ keyword that ~ntpsec~ developers do not recommend
- using; ~ntpsec~ documentation for ~fudge~ is widthdrawn. For local
- hardware providing GPS and PPS time information, ~fudge~ can mostly
- be replaced with use of the ~refclock~ keyword instead.
-
-- ~fudge [address]~ : Tells ~ntpsec~ to consider additional options
- when evaluating the accuracy of time from a given address.
-
-- ~fudge [address] ... flag3 1~ : An option that tells ~ntpsec~ to
- enable "kernel PPS discipline" when interpreting the PPS signal at
- the address. (see [[http://doc.ntp.org/4.2.8p7/drivers/driver22.html][ref]]).
-
-- ~stratum 1~ : Tells ~ntpsec~ to label the source as a "stratum 1"
- time server. This means that it is a clock using NTP that is a
- canonical (?) time source. For example, a stratum 0 NTP time server
- would be an atomic clock. A stratum 1 NTP time server could be a
- clock that uses a GPS receiver to synchronize to said atomic clock.
-
-- ~iburst~ : Tells ~ntpsec~ how often to query a source.
-
-- ~fudge [address] ... flag1 [float]~ : See description of ~... shm
- ... time1 [float]~.
-
-- ~tos mindist [float]~ : Tells ~ntpsec~ to increase the tolerance for
- outliers in the clock selection algorithm. Units of ~[float]~ are
- seconds. The default value is ~0.001~ seconds. This [[http://doc.ntp.org/4.2.6/miscopt.html][reference]]
- indicates that it is acceptable to raise this value for "clocks with
- high jitter and a PPS signal". For the device being configured in
- this guide, this is the case. ~ntpsec~ receives a kernel PPS signal
- on ~127.127.22.0~ indicating when each second occurs but without
- information about which second of the day is being ticked. ~ntpsec~
- receives a coarse time from ~127.127.28.0~ supplied by ~gpsd~ that
- is derived from the NMEA sentences generated by the GPS receiver;
- this coarse time (high jitter) lacks the precision of the PPS signal
- since NMEA sentence transmission times are not well-controlled.
-
-****** Disable DHCP services affecting ~ntpsec~
-Some processes that use [[https://en.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol][DHCP]] (Dynamic Host Configuration Protocol) may
-cause configuration changes to configuration files of ~ntp~. Since
-~ntpsec~ is similar to ~ntp~, it is reasonable to take action to
-prevent this.
-
-Remove some files:
-
-: $ sudo rm /etc/dhcp/dhclient-exit-hooks.d/ntp
-: $ sudo rm /lib/dhcpcd/dhcpcd-hooks/50-ntp.conf
-
-In the "request" block of ~dhclient.conf~, remove ~dhcp6.sntp-servers~
-and ~ntp-servers~.
-
-: $ sudo nano /etc/dhcp/dhclient.conf
-
-For example, the following section of ~dhclient.conf~:
+- ~sudo date -s '2020-07-07T00:00+0000'~ : Manually sets time to a
+ string.
+
+An example output of ~sudo chronyc sources -v~ will show something
+similar to this:
#+BEGIN_EXAMPLE
-send host-name = gethostname();
-request subnet-mask, broadcast-address, time-offset, routers,
- domain-name, domain-name-servers, domain-search, host-name,
- dhcp6.name-servers, dhcp6.domain-search, dhcp6.fqdn, dhcp6.sntp-servers,
- netbios-name-servers, netbios-scope, interface-mtu,
- rfc3442-classless-static-routes, ntp-servers;
+pi@ninfacyzga-1-x:~ $ sudo chronyc sources -v
+210 Number of sources = 6
+
+ .-- 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
+===============================================================================
+#- GPS 1 4 377 21 +110ms[ +110ms] +/- 200ms
+#* PPS 1 4 377 22 +2496ns[+3045ns] +/- 1000ns
+^- vps-2d3ddab6.vps.ovh.ca 2 6 277 57 +1302us[+1304us] +/- 151ms
+^? time.richiemcintosh.com 2 6 1 59 +2626us[+2628us] +/- 92ms
+^- varuna.ga-group.nl 3 6 377 55 -3962us[-3960us] +/- 151ms
+^- ntp3.junkemailfilter.com 2 6 377 58 -4561us[-4558us] +/- 80ms
#+END_EXAMPLE
-should be changed to:
+General references for the ~chrony.conf~ file are:
-#+BEGIN_EXAMPLE
-send host-name = gethostname();
-request subnet-mask, broadcast-address, time-offset, routers,
- domain-name, domain-name-servers, domain-search, host-name,
- dhcp6.name-servers, dhcp6.domain-search, dhcp6.fqdn,
- netbios-name-servers, netbios-scope, interface-mtu,
- rfc3442-classless-static-routes;
-#+END_EXAMPLE
+- The ~chrony~ ~4.0~ documentation. ([[https://chrony.tuxfamily.org/doc/4.0/chrony.conf.html][ref]])
+
+- The ~gpsd~ documentation for communicating with ~chrony~. ([[https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html#_feeding_chrony_from_gpsd][ref]])
+
+- Setup guide for a USB GPS with ~gpsd~ and ~chrony~. ([[https://photobyte.org/raspberry-pi-stretch-gps-dongle-as-a-time-source-with-chrony-timedatectl/][ref]])
***** Disable CPU power saving
Power saving featurs of the Raspberry Pi Zero W may also be disabled
*** Normal Shutdown
*** Unscheduled Shutdown
** Appendix A
-*** Example ~ntp.conf~ for ~ntpsec~
-Below is an example ~ntp.conf~ file for use with ~ntpsec~.
+*** Example ~chrony.conf~ for ~chrony~
+For Raspberry Pi OS, the configuration file should be installed at
+~/etc/chrony/chrony.conf~.
#+BEGIN_EXAMPLE
-# /etc/ntpsec/ntp.conf, configuration for ntpd; see ntp.conf(5) for help
-
-# Drift file
-driftfile /var/lib/ntpsec/ntp.drift
-
-# Leap seconds definition provided by tzdata
-leapfile /usr/share/zoneinfo/leap-seconds.list
-
-# Log file
-#logfile /var/log/ntp.log
+# Welcome to the chrony configuration file. See chrony.conf(5) for more
+# information about usuable directives.
+pool 2.debian.pool.ntp.org iburst
+# This directive specify the location of the file containing ID/key pairs for
+# NTP authentication.
+keyfile /etc/chrony/chrony.keys
-# You must create /var/log/ntpsec (owned by ntpsec:ntpsec) to enable logging.
-#statsdir /var/log/ntpsec/
-#statistics loopstats peerstats clockstats
-#filegen loopstats file loopstats type day enable
-#filegen peerstats file peerstats type day enable
-#filegen clockstats file clockstats type day enable
+# This directive specify the file into which chronyd will store the rate
+# information.
+driftfile /var/lib/chrony/chrony.drift
+# Uncomment the following line to turn logging on.
+#log tracking measurements statistics
-# Comment this out if you have a refclock and want it to be able to discipline
-# the clock by itself (e.g. if the system is not connected to the network).
-#tos minclock 4 minsane 3
+# Log files location.
+logdir /var/log/chrony
+# Stop bad estimates upsetting machine clock.
+maxupdateskew 100.0
-# Local time sources
+# 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
-# Kernel PPS (precision seconds; driver 22)
-refclock pps unit 0 refid kPPS flag3 1 minpoll 4 maxpoll 4 stratum 1
+# Step the system clock instead of slewing it if the adjustment is larger than
+# one second, but only in the first three clock updates.
+makestep 1 3
-# GPS PPS reference (precision seconds; driver 28; root) (NTP1)
-refclock shm unit 1 refid PPS minpoll 4 maxpoll 4 iburst stratum 1
-
-# GPS Serial data reference (coarse time; driver28; root) (NTP0)
-refclock shm unit 0 refid GPS prefer time1 0.109 minpoll 4 maxpoll 4 iburst stratum 1
-
-# GPS PPS reference (precision seconds; driver 28; user) (NTP2)
-refclock shm unit 2 refid PPSuser minpoll 4 maxpoll 4 iburst stratum 1
-
-# Tolerate outliers (useful for coarse clocks)
-tos mindist 0.500
-
-
-# Specify one or more NTP servers.
-
-# pool.ntp.org maps to about 1000 low-stratum NTP servers. Your server will
-# pick a different set every time it starts up. Please consider joining the
-# pool: <https://www.pool.ntp.org/join.html>
-server time.nist.gov iburst
-server tick.usno.navy.mil iburst
-server 0.us.pool.ntp.org iburst
-#server 0.us.pool.ntp.org iburst
-#server 0.us.pool.ntp.org iburst
-#server 0.us.pool.ntp.org iburst
-pool 0.debian.pool.ntp.org iburst
-#pool 1.debian.pool.ntp.org iburst
-#pool 2.debian.pool.ntp.org iburst
-#pool 3.debian.pool.ntp.org iburst
-
-
-# Access control configuration; see /usr/share/doc/ntpsec-doc/html/accopt.html
-# for details.
-#
-# Note that "restrict" applies to both servers and clients, so a configuration
-# that might be intended to block requests from certain clients could also end
-# up blocking replies from your own upstream servers.
-
-# By default, exchange time with everybody, but don't allow configuration.
-restrict default kod nomodify nopeer noquery limited
-
-# Local users may interrogate the ntp server more closely.
-restrict 127.0.0.1
-restrict ::1
+# Get time from GPS (/dev/ttyAMA0) and PPS (/dev/pps0)
+#refclock SOCK /run/chrony.ttyAMA0.sock refid GPS precision 1e-1 offset 0.0000
+#refclock SOCK /run/chrony.pps0.sock refid PP precision 1e-7
+refclock SHM 0 refid GPS precision 1e-1 offset 0.0000 delay 0.2 stratum 1
+refclock SHM 1 refid PPS precision 1e-7 stratum 1
#+END_EXAMPLE
-
-* Discard
-
-** Transitional ntp to ntpsec config file snippet
-# Kernel PPS (precision seconds; driver 22)
-#server 127.127.22.0 minpoll 4 maxpoll 4 true
-#fudge 127.127.22.0 flag3 1 refid kPPS stratum 1
-refclock pps unit 0 refid kPPS flag3 1 minpoll 4 maxpoll 4 stratum 1
-
-# GPS PPS reference (precision seconds; driver 28; root) (NTP1)
-#server 127.127.28.1 minpoll 4 maxpoll 4 iburst
-#fudge 127.127.28.1 flag1 1 refid PPS
-refclock shm unit 1 refid PPS minpoll 4 maxpoll 4 iburst stratum 1
-
-# GPS Serial data reference (coarse time; driver28; root) (NTP0)
-#server 127.127.28.0 minpoll 4 maxpoll 4 iburst prefer
-#fudge 127.127.28.0 flag1 1 time1 0.109 refid GPS stratum 1
-refclock shm unit 0 refid GPS prefer time1 0.109 minpoll 4 maxpoll 4 iburst stratum 1
-
-# GPS PPS reference (precision seconds; driver 28; user) (NTP2)
-#server 127.127.28.2 minpoll 4 maxpoll 4 iburst
-#fudge 127.127.28.2 flag1 1 refid PPSuser stratum 1
-refclock shm unit 2 refid PPSuser minpoll 4 maxpoll 4 iburst stratum 1
-
-# Tolerate outliers (useful for coarse clocks)
-tos mindist 0.500
projects / EVA-2020-02.git / commitdiff