[ntp:questions] GPX18x LVC 3.50 firmware - high serial delay problem workround

David J Taylor david-taylor at blueyonder.co.uk.invalid
Wed Mar 9 07:51:15 UTC 2011

> Hi David,
> I sent off the query/problem to them a few days ago via the online 
> form - alas no reply as yet though.
> I've had problems my end anyway the box this is attached to decided to 
> die and I had to replace the CPU which did all sorts of odd things with 
> the clock and required a change of timer source to stop the thing 
> running mad. It's taken a couple of weeks for it to sort its self out 
> and the jitter/offset to come back down to what they where.
> Anyway if I hear anything back I'll post here.

I hope that Garmin at least acknowledge your request - let's hope the 
delay means that it being passed on.  Sorry to hear about the box 
problems - I replaced my Pentium 133 system with a fanless Intel Atom 
system when that happened.  The 18x is now being used just as a PPS 
reference on my Windows-7 SP1 system (and I think SP1 has stopped the 
glitches I used to see, so better timekeeping), with the NMEA part set to 

# PPS serial port driver - uses serialpps.sys
server  minpoll 4  # PPS using serialpps.sys

# NMEA serial port driver
server  minpoll 4  mode 33  noselect  # 19200bps, NMEA 
serial port

Checking further, before SP1 averaged jitter was 22 - 80 microseconds, and 
after SP1 18 - 28 microseconds, so Windows-7 SP1 has helped the 


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