[time-nuts] Linux time servers

Bob Marinelli bobm at stanford.edu
Thu May 14 22:38:29 UTC 2009


Assuming you are looking for better time than you can get from just  
network servers, you can add a local time source.

EASY WAY

If you want good time at low cost, and have a generic PC, connect  
something like a Garmin 18x LVC to a serial port and install  
FreeBSD.   Easy to configure and NTPD has reported jitter in the 1 to  
4 microsecond range ever since.

Total elapsed time maybe 2 hours including installing FreeBSD and  
mounting the GPS on the roof.

The FreeBSD folks do a very good job of supporting ntpd with local  
hardware clock sources, and document it well.

HARD WAY

Linux with PPS is still more of a work-in-progress and you should  
expect to have to patch kernels etc.  You will find dozens of kernel  
postings, 1PPS seems to have ended up as a serial line protocol,  
AFAIK it is still not in any distribution base kernel.  If you are  
doing an ARM you will likely have to modify the ARM's serial driver  
to do timestamping, by looking at samples in the 8250 driver PPS  
code.  Certainly quite do-able, but not in 2 hours for most people :)

-Bob

p.s. It was not obvious from the Garmin instructions, but all you  
have to do is crimp the serial wires on the 18x LVC to a 9 pin  
connector, placing the yellow 1 PPS wire on pin 1, plug into the PC's  
serial port and FreeBSD does the rest.  Avoid any PC without an  
actual serial port.  You can pick up +5v from your PC (use a fuse).


On May 14, 2009, at 2:34 PM, Randy Scott wrote:

>
> Is there any consensus for the reasons why Linux performs poorly?   
> I was thinking about setting up a server as well (possibly using a  
> little ARM-based single-board computer that runs Linux).
>
> Randy.
>
>
> --- On Thu, 5/14/09, Robert Darlington <rdarlington at gmail.com> wrote:
>
>> From: Robert Darlington <rdarlington at gmail.com>
>> Subject: Re: [time-nuts] Linux time servers
>> To: "Discussion of precise time and frequency measurement" <time- 
>> nuts at febo.com>
>> Date: Thursday, May 14, 2009, 4:23 PM
>> RedHat in the 90s was terrible.
>> It's much better now.
>>
>> Last thing I read about ntp was that it was kind of broken
>> for high
>> precision stuff on Linux and people tend to use
>> FreeBSD.  I duplicated the
>> work of one of the time-nuts by following his site here:
>>
>> http://www.febo.com/pages/soekris/
>>
>> Even with all of the details there it still required a
>> great effort on my
>> part to get things up and running to where I have them
>> now.  If you decide
>> to go this route I will be more than happy to send you a
>> copy of the image
>> on my CF card so that you'll have a working system out of
>> the box.  I had to
>> recompile ntp because the current FreeBSD distro didn't
>> have support for
>> something (NMEA I think, of all things!).
>>
>> -Bob
>>
>>
>> On Thu, May 14, 2009 at 2:09 PM, Dave Ackrill  
>> <dave.g0dja at tiscali.co.uk>wrote:
>>
>>> Anyone got any good Linux time systems for PCs ?
>>>
>>> I now have a PC on my home system that has Linux
>> fedora on it and I'm keen
>>> to learn how to make it a useful new member of my
>> network.
>>>
>>> I did dabble with Redhat Linux once before in the
>> 1990s, and still have the
>>> scars to show for it, so please don't assume that I
>> know what I'm doing...
>>>
>>> Thanks
>>>
>>> Dave (G0DJA)
>>>
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>
>
>
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