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

Rob nomail at example.com
Sat Jan 15 09:09:11 UTC 2011


unruh <unruh at wormhole.physics.ubc.ca> wrote:
> On 2011-01-14, Chris Albertson <albertson.chris at gmail.com> wrote:
>>> When the software (any software) only receives a PPS signal and a
>>> serial message conveying the absolute time, but it does not know how
>>> much the serial message is offset from the true time, how should it
>>> determine the true time?
>>
>>>From a configuration file that describes the relationship between the
>> PPS and text message.
>
> How in the world does whoever set up that config file know that
> difference? The program can use the same algorithm you do to determine
> that. 

It may not have enough information.
When the program only gets PPS pulses and NMEA sentences, it has no
way of telling which NMEA time corresponds to which PPS pulse.

Any system that determines the offset between the arrival of the NMEA
sentences and the time that is indicated in them requires an external
source of correct time to do the calibration, be it either once at
setup time or continuously during use.

With only the GPS device connected and no other time receivers or
network time servers connected, this is not possible.




More information about the questions mailing list