[LinuxPPS] Ultimate time server

[Gerhard Bertelsmann]

I am reading your interesting discussion about a precise time server. Poul
Henning-Kamp
from the FreeBSD universe has done some interesting work using hardware
time stamping
- see link below:

http://phk.freebsd.dk/soekris/pps/

The AMD Elan SC520 CPU has a kind of one-shot counter with a resolution of
33Mhz/4
which could time stamp external events with a resolution of 120ns to get
rid off interrupt
latency/jitter. Poul has also used counters build on FPGAs on standard PCs
an achieved
amazing results. IMHO that is the way some of you try to archive high
accurate time servers.

The Elan CPU is a little bit outdated nowadays. But there are new
interesting ones:
PowerPC derivates
Xscale (ARM)
and Marvell Kirkwood (88F6281 ARM)
Especially the last one is IMHO the most interesting one. It can do IEEE
1588 and PTP external
events time stamping (e.g. GPS PPS) with a resolution of 8 ns. Andy
o'Brien has done
some interesting investigation. He was so kind to share his code. Please
have a look at:

http://lnxpps.de/openrd_utils.tar

The hardware used is OpenRD. Im trying to do this on a cheap Seagate
Dockstar which
is based on the same CPU. There are a lot of other boards, e.g.
SheevaPlug, QNAP TS-119, ...

The code is not ready to use, but it should be a very good starting point
especially gpio9_irq_test.c.

Somebody interested in making a PPS driver ?

Regards

Gerd









Am Di, 28.12.2010, 19:25, schrieb Hal V. Engel:
> On Tuesday, December 28, 2010 05:54:13 am Udo van den Heuvel wrote:
>> On 2010-12-28 14:24, Paul Lavender wrote:
>> > board crystal. Has anybody replaced the crystal with a higher
>> stability
>> > device, such as a temperature compensated crystal, or even better
>> > something derived from the Rubidium maser?
>>
>> I have seen a thermostat built by one of the readers:
>>
>> http://rembl.org/index.php/2008/12/31/thermostat-for-system-clock/
>>
>> Will you also implement a PTP server?
>>
>> Udo
>
> There is also a crystal temperature control device intended for amateur
> radio
> use for UHF and microwave work (moon bounce and the like) from a German
> company.  You basically shrink wrap it to your crystal and give it power.
> I
> think it needed 8 to 14 volts.  So you should be able to power it from a
> 12
> volt supply line from the computer PSU.   It is designed to keep the
> crystal
> at about 42C +-1C.  When I checked into it a while back it was priced at
> about
> $18 so it was not expensive.
>
> There is also a web page out there about someone using a GPS disciplined
> frequency source and a frequency divider to drive the motherboard.  He was
> using a BSD machine and was able to get very accurate results.  Here is a
> link
>
> http://www.febo.com/pages/soekris/
>
> This type of thing does require a motherboard modification so it is not
> for the
> faint of heart or those with bad eyes or unsteady hands.
>
> A more stable freq. source for the motherboard will help things a lot.  At
> that point the limiting factor in how accurate your ntp server becomes is
> latency in the serial interrupt handler.
>
> Hal
>
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