Nrf91 GNSS Almanacs and ephemeris

[Miguel Ferreira]

Hello, I would like to make a question regarding GNSS. So GNSS has a single fix mode (https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/nrf_modem/doc/gnss_interface.html#single-fix) and I would like to know if in this mode the download of almanacs and ephemeris is done. What I think its happening is:

1. GNSS cold start since there is no almanacs and ephemeris
2. We get a valid fix and also wait a few minutes to download the almanacs and ephemeris data
3. The modem reports the valid fix after downloading the data
4. The GNSS is turned off

Thank you for the help!

[Håkon Alseth]

Hi,

 

I would like to know if in this mode the download of almanacs and ephemeris is done. What I think its happening is:

1. GNSS cold start since there is no almanacs and ephemeris
2. We get a valid fix and also wait a few minutes to download the almanacs and ephemeris data
3. The modem reports the valid fix after downloading the data
4. The GNSS is turned off

In the case of a fully cold start, your understanding is close to correct. In Step 2, the fix is reported after all necessary data has been downloaded, like ephemerides, almanac, time of week etc.

The last part, ie. turning off the GNSS, is up to the application. If you are using the gnss sample, there's an option for testing TTFF (time to first fix).

 

Kind regards,

Håkon

[Miguel Ferreira]

Hi,

Thanks for the reply.

Is this information stored in the flash (almanacs and ephemeris) ? So if for example I completely turn off the modem, the next time I turn it on again (in a timeframe of less 4 hours since the ephemeris is only valid for 4 hours) the GNSS will trigger a warm or hot start ?

Thanks again!

[Håkon Alseth]

Hi,

 

Yes, it will store to flash, and start as a "warm" start if there's < 4h.

 

Kind regards,

Håkon

[Miguel Ferreira]

Ok thanks a lot for clarifying my questions! Is there any place where this information can be found ?

Thanks again!

[Håkon Alseth]

Hi,

 

Sorry for not sharing this in my earlier reply.

It is stated implicitly here in the nrfxlib documentation:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrfxlib/nrf_modem/doc/gnss_interface.html#deleting-gnss-data-stored-in-nv-memory

 

Kind regards,

Håkon

[Miguel Ferreira]

Thank you again! Will close this ticket :)