[time] GPS Time Server Survey

Chris Kuethe chris.kuethe
Thu Apr 24 20:45:55 UTC 2008


On Thu, Apr 24, 2008 at 9:14 AM, Kipton Moravec <kip at kdream.com> wrote:
> I am designing a system with a GPS module, and started looking at all of
>  the things it could do, including time.
>
>  Since you folks are all interested in time, I was wondering which of two
>  products would be of interest to you.
>
>  1. A GPS module with the ability to expand the serial port to more than
>  10 to allow you to use the NTP NEMA driver. The time pulse would be
>  accurate to about 30 nS RMS. Retail cost about $100.

yes. although i'm wondering where you're going to get such a
non-crappy chip. Also, will it output raw measurements (CP/PR/D)?
While you're at it, could you mount this on a (mini)?pci card with a
dual-port UART - plug it in, it looks like 2 more com ports, but then
you can use one port as your time source and the other port for
"control" purposes.

>  2. A time server with 2 Ethernet ports, with GPS time reference, to
>  directly support between 50 and 100 users using GPS. Retail Cost about
>  $200

could be fun - depends on what's in it.

>  Both would be Stratum 1 by using the GPS (and later Galileo also)
>  Satellites.
>
>  Any additional specifications? How much more would you pay for the
>  additional specs?
>
>  Or is this not interesting enough for you, that I would be wasting my
>  efforts.

my home time server is a soekris net4801 driven by a garmin gps18;
pretty low-end, but internal diagnostics say that it's tracking within
1 usec of the garmin's PPS output. that's tolerable, considering the
garmin is only specified to 1 usec accuracy, and the 4801 isn't really
a marvel of computing precision. And the fact that it's
ethernet-connected to the ass end of an ADSL line - there goes all my
precision anyway.

also, the soekris can support more than 100 users; i've seen 182
unique ip's today, and the day is barely half over.

as i'm also a bit of a gps nut, i like the fact that i can run gpsd on
my time server to get a view on how the GPS is performing, as well as
being able to generate a sky view (http://gpsd.mainframe.cx/). For
that matter, I like the fact that I can put perl/php/python on this
machine and whip up little scripts as it need them. So a cute little
low-power SBC would be neat, but I hope it's not too low-power...

CK

-- 
GDB has a 'break' feature; why doesn't it have 'fix' too?



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