sync time problem

0 votes

dear all,

I use one device with U-blox UBX-G7020-KT system (DIYmall VK16E GMOUSE). I get a data and time information by a serial cable and I use a 1PP rising for sync with my application.

When I start a system after 10 or 12 hours I have a not good time (for example 1,5 or 2 seconds more). After more reboot of my system this problem disappears.

Please help me.

by nowire asked Apr 19, 2018
+1 vote
Restating what I think you describe: you start the GPS and it works fine. You turn it off but V_BCKP is retained to maintain RTC and BBRAM, then whe you reapply VCC, the time in the NMEA messages at startup is off by 1 or 2 seconds.
This is expected behaviour since, in backup mode, RTC can drift by several seconds in 12 hours  when temperature changes (50 ppm frequency error over 43200 seconds is about 2.2 seconds)
For correct time you (a) must wait for a valid position fix to be declared, (b) as grumpy states: wait for up to 12.5 minutes more for the leap-second correction to be applied
by grampy answered Apr 19, 2018
by grampy edited Apr 19, 2018
thank you for the fast and good replay.

I try it indoor and outdoor, but I have always 4 or more satellites. Now I have disable all NEMA message and I have enabled only GxZDA message. I not need position.
I think that the problem is that I not wait 12.5 minutes. I try wait this time.
There is an information that tell me if the time is correct or no?

very very thanks!!
0 votes
Does receiver have position data?

Is antenna indoors?

You need good coverage for GNSS to get a fix and get time.

Also receiver needs to download leap second info (sent by satellites once every 12.5 min).
by grumpy answered Apr 19, 2018
0 votes
Ciao grumpy,

yes, the receiver hava a data position.
The antenna is outdoor.

I try to wait mor than 12.5 for get a good time.
I try also to read NAV-TIMEUTC message for get information on bitfield valid. I don't know if my version of GNSS have this message. I check it this evening.

by nowire answered Apr 19, 2018
Dear grumpy,

I still have a problem in time sync.
In my application I have two DIYmall VK16E GMOUSE connected with serial cable at two arduino card. I have connected the 1PPS exit at arduino interrupt input pin.
On the DIYmall I have disabled all NEMA message and I have enabled only NEMA GxZDA message every second.
I send the message NAV-TIMEUTC for check the UTCTIME sync bit. When the sync bit becomes true, I wait the falling edge of PPS signal, read the GxZDA message and start the PPS interrupt, when it is rising i set the data end the time in the RTC 5ppm in my card.

The problem is that my two card haven't the same time. The time is differ from 500ms to 1500ms or more.

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