Accessing accurate GPS Time via MavLink

[nothsi]

Hello,
to be able to add reliable timestamps to data gathered by different M4s I wanted to ask, if (and how) it is possible to access the M4s GPS time of week via a MavLink Message.
So far I requested the AQMAV_DATASET_GPS_XTRA via a COMMAND_LONG message but I am not sure whether the 8th parameter contains the wanted value.
In it seems as if qgroundcontrol is able to access the TOW?
Any input would be greatly appreciated.

[rput]

This would be very useful to have. It seems right now the TOW is only logged, but not transmitted through mavlink. Is this correct?

[Max]

That's correct. I'm actually not sure there is a MAVLink message type to transmit iTOW.

Nothsi, I think the parameter you're referring to is only an internal timestamp of when the last GPS reading was received. This would be micoseconds since boot, not actual time.

If you can compile the code yourself, it should be fairly trivial to add gpsData.iTOW as another parameter sent in the GPS_EXTRA dataset... I'll add it also, but not sure when those changes will make it out of "the lab."

-Max

[rput]

Great, thanks Max!

I will see if I can compile it myself. On another note: I noticed that there is a flag in the ublox code for DO_RTK_GPS which enables raw data output from the LEA-6T receiver. Would you know if this data also gets logged if the flag is enabled, or is logging this not implemented?

[Max]

Check at the top of gps.h file -- you can un-comment GPS_LOG_BUF and GPS_FNAME to enable logging the raw data to a file. You can also enable GPS_DO_RTK and GPS_DEBUG here to log more data. I'm not sure I've ever tried this myself, but I imagine it should work.

You can also enable direct passthrough of GPS data to an AQ serial port. Pick a serial port (AQ6 has 2 and M4 has 1) and set the corresponding COMM_STREAM_TYPx parameter to a value of 8 and COMM_BAUDx to some non-zero value (eg. try 230400). Perhaps it goes w/out saying, but you can't have Mavlink data and the GPS passthrough on the same serial port.

Lastly, if using the M4 USB port, setting the baud rate to 1200 (on the connected computer) will automatically enable GPS data passthrough as a serial data stream via USB.

-Max

[nothsi]

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