|Subject:||Re: Time precision in gps_fix_t|
|Date:||Wed, 22 Jan 2020 13:43:25 +0100|
|User-agent:||Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1|
thanks for the reply. I am aware of it, but for the application I
am working with now, the host system cannot access a PPS line. I
can see the UBX decoding in the GPSD logs, and I would really like
to be able to access that information.
When I do a gps_read and retrive the gps_data_t, for what I understand I get back the JSON object TPV.
Is there any way I can access the decoded UBX with gps_read?
As the driver decodes it, I assume it should be known to GPSD right? what I am interested in is to expose the decoding of UBX-GPSTIME. Any way I can achieve that?
Like Gary said, PPS is what you should be looking at for your application.The ubx sentence with microsecond resolution is mostly useful for post-processing of position data.The serial transmission and string processing is inherently non-deterministic, and will have jitter. And the clock you read will have latency issues.From an u-blox manual:(and that is before data goes through the uart, serial line and through the receiver end processing. Maybe a serial/usb interface with buffering as well)
You should read up on the Timepulse outputs (there should be 2 on the ubx-m8030), and how you can access them on your development card, or what you have available.The pinouts don't seem to be publicly available, so you may need to contact u-blox.
If you are looking for references on high precision time synchronization I think this site has lots of information:
ons. 22. jan. 2020 kl. 04:09 skrev Marco Spanghero <address@hidden>:
I am using GPSD for research purposes about high precision time synchronization.
I wrote my own client in C that gets a structure gps_data_t that contains gps_fix_t. I am trying to access the time with a higher resolution than 1s.
The module I am using is a ublox ubx-m8030 that can output a ubx sentence with specific timing down to microseconds as I can see in ucenter software.
My questions are:
why the field time in gps_fix_t, even if it has second and subsecond field, the subseconds field is set to 0 in all measurements?
how to I access the ubx time sentence from gpsd?
where can I access a high resolution time information? I know GPS should do better than 1s, 100us should be reasonable.
Any help would be highly appreciated.
KTH Royal Institute of Technology
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