nrf9160 modem XFILEWRITE gps almanac

[LordLucan]

Hi,

I see in the nrf9160 1.2.0 AT document there is a command XFILEWRITE that suggests the GPS almanac can be written and persist in the modem.

Can you provide more documentation on this command and the format of the data you can write?

I'd like to improve the TTFF for the GPS. I've got the SUPL GPS client example working and it does indeed speed up TTFF to a few seconds. But I'd like to be able to store that information in the modem in cases where I have no LTE connection or it is simply unavailable for other reasons. That is I want the GPS data to persist. Suggestions welcome!

Regards,

Paul

[Simonr]

Hi Paul

A graceful power-down in this context is referring to a graceful power-down of the modem, as specified in the documentation here. If you're powering down the modem by using AT+CFUN=0 the almanac will be stored to flash. 

Best regards,

Simon

[LordLucan]

I've also done a bit more work on this trying to discover why gps TTFF is so slow.

What I've noticed with the GPS SUPL sample is that in nrf_scoket.h there are a number of constants NRF_GNSS_AGPS_* that are used to write AGPS data to the modem. Thinking about this a bit more maybe the issue is that from a cold start the GPS modem needs to get either the current UTC time or an approximation of the current location for faster TTFF.

So I've now modified your GPS sample to filter out NRF_GNSS_AGPS_EPHEMERIDES and NRF_AGPS_ALMANAC. If I do this then the GPS locks quickly in a few seconds still. So, I'm thinking that almanac/ephemeris data is persisting but what is required is either position or time to be uploaded to the modem.

So the question is. Can you please document or point me to the details of the data formats for the NRF_GNSS_AGPS_* constants? I'd like to set these myself without having to connect to the supl server.

Just generally, Nordic have done a great job with the nrf9160 but we as customers should not be having to reverse engineer how the GPS works in order to get good performance. This should all be documented somewhere.

Regards,

Paul