[SOLVED]Adjust both hwclock and date

YTW · n00b Joined: 30 Aug 2016 Posts: 65 Location: Taiwan

Both hwclock and date are the same
But both of them are incorrect time.
What should I do for updating them correctly via network instead of manually setting.
(I don't want to set them referring to my watch by hand because the unit of second must be wrong.)

fedeliallalinea · Posted: Thu Sep 01, 2016 2:28 pm Post subject: Re: Adjust both hwclock and date

YTW · n00b Joined: 30 Aug 2016 Posts: 65 Location: Taiwan

2 following questions:p

I only added these two lines in the default /etc/ntp.conf

fedeliallalinea · Posted: Thu Sep 01, 2016 4:06 pm Post subject:

YTW · n00b Joined: 30 Aug 2016 Posts: 65 Location: Taiwan

yes. I think you are right.
I already rc-update del ntp default and rc-update add ntp-client default.
So if network is connected and service didn't start at boot, I can

fedeliallalinea · Posted: Thu Sep 01, 2016 7:25 pm Post subject:

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

My config is fairly typical I think:

http://bpaste.net/show/1d2ac9a0dbdb

I have a stratum 1 ntp server in my house, based on gps. So that's the 192.168.1.2 line. You'll want to take that out.

YTW · n00b Joined: 30 Aug 2016 Posts: 65 Location: Taiwan

NeddySeagoon · Posted: Fri Sep 02, 2016 8:04 am Post subject:

YTW,

Yes.

GPS is an atomic time standard. When your GPS receiver works out where you are it also has to work out when you are too.
It solves four simultainious equations to get latitude, longditude' altitude and time.
It actually gets two solutions, one near the surface of the earth and one out in space.

With a fixed GPS receiver, its possible to average the position in space, so that the only unknown is time.
That gets you a very good time standard.

The down side with my GPS atomic time standard is that its on a Raspberry Pi, which has ethernet over USB, so the jitter could be better.
You get your very own stratum 1 atomic time standard. NTP pools are usually stratum 3.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

cwr · Veteran Joined: 17 Dec 2005 Posts: 1969

I use an ntp.conf of:

YTW · n00b Joined: 30 Aug 2016 Posts: 65 Location: Taiwan

I got it!
Thank you all for suggestion and knowledge.

depontius · Advocate Joined: 05 May 2004 Posts: 3509

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

It seems that Neddy probably read the same website I did. Mine's on a pi b+.

I have:

pi b+ v2 (single-core)
adafruit ultimate gps v3
an external antenna (must have!)

There's also a board specifically designed to mount the gps onto a pi, I'd recommend that, and a case.

AFAIK all the pi's share the usb/nic issue so jitter doesn't really improve with a better pi. I'd research that to be sure and then:

If it's true then go with the cheapest pi
If it's not then get the one with better throughput.

I'm about USD $100 all in, including shipping. This is significantly cheaper than a commercially-available gps-based stratum 1 time server.

I'm using Raspbian with the gui stripped out. I used this site for instructions, and links from it http://www.satsignal.eu/ntp/Raspberry-Pi-quickstart.html

The down side is every time you do a dist upgrade you pretty much have to fix it. The instructions are a little different every time, and a pi is not a rocket for compiling so that's a drag.

The up side is it's like a mini vacation from my real job. Which actually requires a good time source.

I had a pi b+ running Gentoo, but the 'disk' went wonky and I haven't put it back up. About all it ever did was run gentoo, no real tasks.

I've thought about pulling the gps chip out and putting it in my router box (http://www.supermicro.com/products/motherboard/atom/x10/a1srm-ln7f-2758.cfm) where it could be a really high quality time server, but haven't gotten around to it. This box is also running VMs and a router so I don't really want all my eggs in one basket.

Edit: About the antenna. I did this without the antenna first, the GPS got a link about 80% of the time when outdoors, about 60% of the time when in a window with good sky access. The battery on the gps is a must for fast booting. When I got the antenna I could put the pi anywhere I want as long as the antenna is outside, and I always get a fast link to the gps.

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

When you do this for a pi, you need to google <year> raspberry pi gps time server because there's always something new out there, and somebody upstream probably changed something important.

If you're not using raspbian you may want to try googling your distro too.

The instructions are often dummied down so you may have to reverse engineer what they were saying. The link I gave is fairly straightforward and has been actually maintained pretty well over multiple dist-upgrades.

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

Actually if you're trying to do this then you might want to look at other boards which don't have the ethernet-over-slow-usb problem. The idea behind a time server is that constant conditions make more accurate timekeeping, so in my opinion that means having a box that does nothing but keep time, in a constant-temperature environment, is a good thing.

I haven't really done that research, but I've done a little bit of research for my next micro-linux box. Something like a minnowboard (which I think is discontinued) would be alright.

NeddySeagoon · Posted: Fri Sep 02, 2016 7:03 pm Post subject:

depontius,

My system is an early Pi B (one of the first 10,000). The guide I followed has a warning notice now.
I have the internal patch antenna too.

During commissioning, it worked well on a South facing window sill. The GPS satellites are in inclined orbits that mean they never get overhead from the UK.
Until you have the GPS ephemeris, transmitted from the gps satellites, the poor wee thing doesn't know where the satellites are. That's important, because the CA code is transmitted spread spectrum and the centre frequency is affected by a variable doppler shift related to the satellites motion, that needs to be compensated for.
Acquiring the first satellite is hard. It may take hours. Once that's done, the system knows about all the rest.
If you are impatient, you can provide the ephemeris and sync time to network time.

You can't get the P-code. Its encrypted. For a GPS ntp server the CA code is good enough.

I use the patch antenna indoors, sort of, its in my garage, that has a corrugated fibre (asbestos?) roof that is covered in moss.
It claims it can see 13 satellites, which I don't believe. That's over half the constellation.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

In addition, ntp sometimes decides that a server it was using is no longer stable for some reason, like the route is down or there's a lot of latency to the server. My other boxes sometimes decide that a different time server is better for a little while.

Ant P. · Watchman Joined: 18 Apr 2009 Posts: 6920

This thread reminds me of something I've wanted to do for a while: I've got no shortage of rooted Android phones with GPS receivers built in. I've looked a few times in the past for some way to coax them into acting as an NTP/GPS local network server, but never found anything of the sort...

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

I've seen ntp for rooted android phones, but I question the value of a stratum 1 time server over wifi. I'm not sure the latency is low enough to work out.

cwr · Veteran Joined: 17 Dec 2005 Posts: 1969

I used an Adafruit Ultimate GPS breakout board with an Atmel AVR 382p
(the basic Arduino CPU) to build a time server. It supplied time via the
serial port, but with an Arduino Ethernet I suppose it could have supplied
it via Ethernet.

I tried one of the long-wave time signal stations, but for some reason could
never get a reliable signal lock.

Will

NeddySeagoon · Posted: Sat Sep 03, 2016 6:52 pm Post subject:

cwr,

A long time ago approx 40 years? a magazine called Wireless World published a series of articles describing a radio time code clock all made with TTL logic.
I still have the articles somewhere, along with my implementation of that clock.

I don't think I ever got the RF (60kHz) bit right, since I could never detect even the slow code.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.