[aprssig] gpsd and ntpd

Joe Bennett aprs at ka3nam.com
Fri Mar 15 09:19:50 CDT 2013


Yes, GPSD manages the GPS and NTP uses a shared memory resource to 
integrate with GPSD. Without any decent testing, I'll grant that there 
has to be some indeterministic processing time involved, but it can 
certainly keep things well under 1 ms. Some others on the net have 
claimed the configuration can keep things under 100 us but I personally 
have not seen that (it may be the hardware I'm using). Typically 500 us 
to 1000 us... Can't get that with NTP alone... Good enough for me and 
what I need to do with it...

Other than searching the net and finding the multitude of ways that 
others have tried, I have a doc that I can share that shows how I did it 
via Ubuntu server 10.04. I'll see if I get some time to post it on the 
web...



-Joe
KA3NAM

On 03/15/2013 08:08 AM, Jason KG4WSV wrote:
> On Fri, Mar 15, 2013 at 7:58 AM, Joe Bennett <aprs at ka3nam.com> wrote:
>> Yep, it can be done... Have a few NTP servers configured this way with
>> PPS... Deffinately keeps the server more accurate than NTP alone... Getting
>> date and time from GPS depends on the GPS used, as jitter can be quite high
>> and hard for NTPd to correlate..
>
> Just to clarify Joe:  Are you saying it can be done by letting gpsd
> control the GPS and let NTP talk to gpsd?
>
> I know GPS can be a clock source, but gpsd is a service that owns the
> GPS and hands out data to programs on the system/network that need GPS
> data.  I really don't see how that's compatible with rather strict NTP
> timing requirements.
>
> -Jason
> kg4wsv
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