I've a ublox M8N GPS, and configuring it via MissionPlanner's MAVserial pass function because I don't have FTDI cable for the moment, and ublox's u-center v8.18.

The issue is, that not all the settings are stored in the GPS, some stored, and some not.

I need to almost reconfigure the GPS after every power up.

Any idea what's going on here?


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Jani, are you saying the Chinese are actually copying the M8N completely? And that they leave the Flash memory off?  Somehow I doubt it...

Anyway, The Neo - N series ( M8N, Neo-7N) all have Flash internal to the GPS device. They also have RAM. The RAM stores Ephemeris/Almanac from Sats, to enable Fixes to take place. An initial fix will take up to 30/35 seconds with good sky view - this is due to the download period of said data. Subsequent fixes are much faster  - 2 to 5 seconds, for up to between 3 and 4 hours, at which time there will be a long fix period again - 15 to 35 seconds - while Sat data is updated, and then short fix periods again - this repeats every 3-4 hours.

All the Sat data is stored in RAM.  If you do not have battery or supercap backup on the RAM ( Pin 22) then each time you power down the GPS the Sat data is lost, and a power on requires the data to be downloaded again, with a long fix period - 35sec or so. This is all done by the GPS itself - no user intervention or action, no autopilot action either.

The GPS configuration setup , if changed from default,must be saved to the GPS device for it to be persistent. The setup will be retained in RAM till power down, and in some versions of device, in the battery backed RAM. For permanent save, the save must be user commanded, and saved in internal Flash ( -N devices only! -M devices have no Flash). On power on, the GPS will obtain the setup from the permanent store and use it, unless changed by the user ( autopilot or whatever).

As said, these devices do not need flash to work, only to save the setups..or if you setup the GPS  to log GPS data/position, etc, automatically. However, they have to store the operational firmware somewhere, either in Flash ( -N) or ROM (-M)

The Neo-7N and Neo-M8N are both flash based, the M8N is more sensitive than the 7N, and the N series draw approx 10 to 15mA more than the 7M  and M8M ( flashless- ROM based) devices - for what its worth.

The Nampilot...

Hmm half of my last message just disappeared... Weird.

Yes they can work fine without flash memory. You just loose settings and it goes always to factory settings after powercycle. We have custom made settings that we upload to all our GPSes and we want to safe those to nonvolatile memory and that's why we have small memory chip on board. There are some settings that are not uploaded during reboot. Memory chip that we use has SOT23-5 case and it connects with I2C to main GPS chip. That's the way how those GPS chips are designed to work.

Only navigation almanac stays on GPS chip if there is backup battery available.

@Gisela, No i don't say that Chinese copied those chips. That's the way how they have been designed. And like you said, yes they store only almanac on main chip nothing else. If you need to save settings you need external memory for that.

Nampilot, thank you very much for your explanation

Jani, what do you mean by 'That's the way how they have been designed' - designed by who? The UBLOX Neo-7N and M8N have internal RAM that can be battery backed up, AND internal Flash that stores operating firmware, any config setup data that is commanded to be saved ( UNBLOX command message) and GPS logs, if so setup. There is no  UBLOX Neo7/8 -N device without internal flash, or are you saying the Chinese make one without?? Then it must have ROM for firmware, and then it is a -M and not -N...

The 7N and M8N can have additional Flash attached via I2C, but it is not needed at all, unless you need more flash memory size ( internal is 16Mbits...)

If you wish to use the 7M or M8M, ROM based, then you must use external flash..

You do NOT need external memory/flash to save setups on the -N series...

The Nampilot...

any solution ? facing the same problem.....

Solution for the moment, to solder a switch to the TX cable coming out from Pixhawk. This way you can enable/disble programming.

Or wait till GPS parameters owerwrite can be enabled/disabled from upcoming version of MissionPlanner.

I am beginning to think we are just victims of cheap Chinese M8N knock-offs.  According to Ublox they are all supposed to be "future proof", with built in internal flash like G+J Noci have already stipulated.  However,  when I have tried to reflash some of my Chinese modules the settings just aren't there upon reboot.  I know that it is not my FTDI, as I am able to reflash some of my more expensive Modules.  I am beginning to think it is in the knock-off chip design itself.  

I did notice that when the modules in question were plugged in for the first time they worked, but if I left them plugged in during a firmware update they would become nonfunctional.  Refresh rate on all of them would be at 1Hz after update.   Maybe someone with better knowledge of these board layouts will have a better idea of just what is going on.  I haven't looked any further into it myself, but now that I see that it is not just me I will look more into it.  

If pixhawk uses same configuration on wiki page (link) , gps doesnt accept some commands on that config file. You have to do it manually with u-center.

I explained here

I had the same problem guys with my M8N Drotek GPS. Settings I manually changed never persisted even after writing them to flash.

The workaround I found that fixed this was to upload the configuration file provided in the WIKI.


Despite this, the baud rate still reverts back to 9600 whenever i connect to UCenter however the rest of the parameters seem to stick.

Hope this helps.

Hi  Arshish,

I also have a drotek gps but I do not have problems.

In UCenter after you have finished your settings in Configuration go to the CFG (Configuration) tab select as per image below and click send. Let me know if it solves your problem


Thanks Paul.. Ill try try this today.

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