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[gpsd-users] u-blox binary time issue

From: Deven Hickingbotham
Subject: [gpsd-users] u-blox binary time issue
Date: Tue, 16 Apr 2019 13:49:17 -0700
User-agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1


Last year we discussed an issue with missing fixes from a u-blox 7 receiver. Since then I've been trying various solutions, but concentrating on using the u-blox binary protocols.

To get gpsd 3.16 (Raspbian) working with u-blox I have to run gpsd with the -b option otherwise gpsd always turns on the NMEA messages.

For gpsd to be fully functional (meaning cgps works), I have to use u-blox's PVT, SOL, and SVINFO messages. Anything less and cgps is missing data.

I have a Python app that calculates the gps latency and it is generally 0.1 seconds. BTW, I use chrony set set my system clocks.

But after configuring the u-blox receiver to deliver only binary messages, the latency was -0.9 seconds (meaning the gps timestamp was ahead of the system time). This is exactly one second off from what it should be.

I tried setting different gps update rates (1 second and 0.25 seconds) and the latency was still -0.9.

When I switch the u-blox back to only NMEA messages, latency returns to normal. This is without rebooting, so the system clock is the same for all calculations.

I tested using both u-blox 7 and 8 receivers.

Any idea what might be going on?


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