William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ un...@physics.ubc.ca
Canada V6T 1Z1 ____|____ and Gravity ______|_ www.theory.physics.ubc.ca/

On Sat, 6 May 2017, Deven Hickingbotham wrote:

I have a GPS app that runs on a Raspberry Pi. The system is powered off most of the time, but on startup needs to sync time very quickly using PPS.

It looks like the makestep directive is the way to do this. Which of the following would be better?

makestep 0.01 10

makestep 0.01 -1

The first would make adjustments during the first 10 updates, while the second would do so continuously, correct? Note: none of the apps running

The second would be silly. The whole point of chrony is to discipline the
clock so that it is both monotonic AND very very (usec) close to UTC, so
letting chrony do its job is clearly the way to go. yes, one can "jump" for
the first couple of measurements to get rid of the intial time offset but then 
letting chrony
figure out how badly the rate of the onboard clock is from one second per
second and how far out the actual time is, is the way to go. Ie, the clock
will not be out by 100ms anyway after the first one or two measurements.

would be adversely affected by jumps in the clock (they would benefit by having more accurate time).

Here is my complete configuration file:

server 0.us.pool.ntp.org iburst
server 1.us.pool.ntp.org iburst
server 2.us.pool.ntp.org iburst
server 3.us.pool.ntp.org iburst

Those are there why? And why the iburst?

refclock PPS /dev/pps0 lock NMEA refid PPS
# Setting for 2, 3, 4, 5, 10 updates per seconds

Huh? What kind of PPS do you have?

refclock SHM 0 offset 0.1 delay 0.2 refid NMEA noselect

# In first ten updates step the system clock instead of slew
# if the adjustment is larger than 0.01 second.
makestep 0.01 10

That will really only be effective the first time.

# Enable kernel synchronization of the real-time clock (RTC).
Does it have an rtc at all?

# Allow NTP client access from local network.
allow 192.168
allow 172.20

To unsubscribe email chrony-users-requ...@chrony.tuxfamily.org with "unsubscribe" in the subject. For help email chrony-users-requ...@chrony.tuxfamily.org with "help" in the subject.
Trouble?  Email listmas...@chrony.tuxfamily.org.

Reply via email to