[ntp:questions] Using Trimble TSIP under Linux

David Taylor david-taylor at blueyonder.co.uk.invalid
Mon Nov 26 17:42:30 UTC 2012

On 26/11/2012 14:12, DaveB wrote:
> Ah, but it does, on the GPIO port, but it's logic is at 3.3V levels, not
> even TTL, so take care.
> I've yet to make use of it myself though, and I forget what it shows up
> as in Linux.
> I did find however, that the LAN port has some strange latency
> behaviour, then realised (from Linux's device listing) that the LAN port
> is in reality a USB<>LAN converter.
> Regards.
> Dave B.

Thanks for your reply, Dave, and I take your point.  You will find that 
I have since updated my project page:


to describe the use of the GPIO 3.3V serial port.  For NTP purposes, the 
post is incomplete, as it does not have a conventional DCD input where 
the PPS signal would normally be fed, but there is a work-round with a 
GPIO PPS driver someone has written.

On a quick check at the moment, the Raspberry Pi shows a stratum-1 
server reached over the LAN to have an offset of -0.028 milliseconds, 
whereas its own PPS source is reported to have an offset of -0.001 
milliseconds.  Is that the right sign and amount for the offsets you 
might expect comparing the LAN input and the GPIO pin interrupt for the 
PPS source?
Web: http://www.satsignal.eu

More information about the questions mailing list