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Old 01-04-2021, 08:53   #1
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Join Date: Apr 2021
Posts: 2
Fragmented NMEA Messages - u-blox 8/m8

Good morning,

I'm posting on behalf of my client who has had me setup a laptop for charting purposes. Laptop is a Latitude Rugged 5420 with the optional dedicated GPS card installed.

The card will provide a fix to u-Center and the Rugged Control Center app. When in OpenCPN I can see the GPS connecting and dropping. Usually 2-3 bars for a few minutes solid then dropping to the red circle for a second back to 3 bars, back to red circle, connect for a minute or two, etc.

When looking at the NMEA Debug window, I see massive blocks of fragmented NMEA sentences. I've pasted an example below.

I see some fragmented sentences in the Debug window with each refresh of the window but the volume increases greatly when the GPS signal drops.

Has anyone seen this behavior before? I've re-setup the connection, double-checked connection settings (9600 baud, 8 data bits, 1 stop bot, No Flow Control, No Parity). I've made sure all sentences are setup to be accepted by OpenCPN as well and see them GREEN in the console when they hit.

I'm aware of the current driver posts but I was not sure if this was the same behavior described. Thank you in advance for any help!

Code:
<MAROON>20:08:30 (Serial:COM7) M,,*4D<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) .12*1C<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) 2*14<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) 4*7E<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) 5*75<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) 9*76<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) ,*68<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) ,*65<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) 8*69<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) A*69<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) ,*68<0x0D><0x0A>
<MAROON>20:08:30 (Serial:COM7) 9<0x0D><0x0A>
<MAROON>20:08:31 (Serial:COM7) GNGRS,000828.00,1,-2.9,-10.2,-5.9,5.9,-7.9,-3.1,6.4,10.1,,,,*79<0x0D><0x0A>
<MAROON>20:08:31 (Serial:COM7) GST,000828.00,45,,,,5.7,3.2,6.3*4C<0x0D><0x0A>
<MAROON>20:08:31 (Serial:COM7) ZDA,000828.00,01,04,2021,00,00*7E<0x0D><0x0A>
<MAROON>20:08:31 (Serial:COM7) GBS,000828.00,5.7,3.2,6.3,78,,-5.8,61.7*44<0x0D><0x0A>
<RED>20:08:32 (Serial:COM7) <0x01>
<RED>20:08:32 (Serial:COM7) <0x1E>1$
<MAROON>20:08:32 (Serial:COM7) VTG,,T,,M,0.074,N,0.138,K,A*34<0x0D><0x0A>
<MAROON>20:08:32 (Serial:COM7) GNS,000829.00,3651.47246,N,07558.83716,W,AA,16,0.90,14.5,-36.2,,*6B<0x0D><0x0A>
<MAROON>20:08:32 (Serial:COM7) GGA,000829.00,3651.47246,N,07558.83716,W,1,12,0.90,14.5,M,-36.2,M,,*45<0x0D><0x0A>
<MAROON>20:08:32 (Serial:COM7) GSA,A,3,28,04,17,25,02,12,19,06,,,,,1.43,0.90,1.12*11<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GNGSA,A,3,65,79,81,78,71,72,87,88,,,,,1.43,0.90,1.12*16<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GPGSV,3,1,10,02,57,296,27,04,10,054,27,05,17,208,,06,62,022,24*7E<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GPGSV,3,2,10,09,19,086,21,12,44,297,13,17,36,108,28,19,56,092,36*7D<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GPGSV,3,3,10,25,11,322,29,28,06,163,09*76<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GLGSV,3,1,10,65,43,136,19,71,11,027,26,72,44,069,22,77,16,215,*62<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GLGSV,3,2,10,78,33,272,15,79,15,325,23,81,08,291,24,86,03,088,*66<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GLGSV,3,3,10,87,49,036,30,88,47,330,28*69<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GNGLL,3651.47246,N,07558.83716,W,000829.00,A,A*60<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GNGRS,000829.00,1,26.7,2.9,5.1,0.9,5.7,-6.8,-0.6,-4.8,,,,*4D<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GNGRS,000829.00,1,-4.4,-8.7,-7.5,-2.0,-9.1,-3.0,4.5,9.6,,,,*59<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GNGST,000829.00,77406,,,,5.7,3.2,6.3*7E<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GNZDA,000829.00,01,04,2021,00,00*7F<0x0D><0x0A>
<GREEN>20:08:32 (Serial:COM7) $GNGBS,000829.00,5.7,3.2,6.3,,,,*5A<0x0D><0x0A>
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Old 01-04-2021, 09:21   #2
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Re: Fragmented NMEA Messages - u-blox 8/m8

In your sample from 20:08:32 there are 931 (+/- a few, I did a very quick takeoff) serial characters. 9600 baud supports 960 characters/bytes per second. With a turnaround time after each message (there are 17 messages in your one-second sample) of around 10ms, that actually leaves a capacity of 0.83*960=800 characters/second. So, it would appear you are overflowing the capacity of a serial connection at 9600 baud.

Two options; increase the baud rate or decrease the frequency at which data is transmitted.

BTW, welcome to CF.
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Old 01-04-2021, 10:08   #3
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Re: Fragmented NMEA Messages - u-blox 8/m8

Hey thanks for the heads up, I'll give that a try and I thought it may be something weird like that going on. I'll give it a shot!
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Old 01-04-2021, 12:58   #4
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Re: Fragmented NMEA Messages - u-blox 8/m8

I have a similar chip, M8030KT. I have it only outputting GLL, GGA, VTG, ZDA, RMC. The GSA and GVA sentences seem to spam the output a lot. Also, I have mine setup to only use GPS satelites (GP talker ID only).

Mine is 4800 baud though.
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Old 01-04-2021, 13:35   #5
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Re: Fragmented NMEA Messages - u-blox 8/m8

I'm happily using a Dell Latitude 12 7202 Rugged Tablet for the same purpose. But I gave up on trying to get the miserable embedded GPS to work long time ago. Disabled it in boot menu and now using a 50 dollar Chinese USB GPS. Works like a charm.
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Old 01-04-2021, 13:50   #6
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Re: Fragmented NMEA Messages - u-blox 8/m8

That is what is in the $50 chinese GPS. MT8030KT knockoff or a series 7 equivalent. I opted for the series M8 knockoff.


Highly customizable when they are working. U-Center software is very confusing / broken / buggy. Not a fan of it. But it does work. I had to change the configuration in MSG then update the settings using CFG - CFG, screen. There is another screen to change the baud rate as well.



If you turn off the 2 sentences I mentioned, no excessive messages now.



Not straightforward.
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