NRF9160 GPS Reboot

[Thomas]

Hi,

How can I make the modem start a hot fix after rebooting the nrf9160?

I am getting a GPS fix, then powering down the modem with CFUN=0, which should be saving the ephermeris to flash? Then I am rebooting the system with sys_reboot(0). Once the device reboots I am sending the last fix reported using GPS_AGPS_LOCATION, and am sending the current time using GPS_AGPS_GPS_SYSTEM_CLOCK_AND_TOWS. However, the modem is still doing a cold start.

Is there something else I need to send? 

Kind regards,

Thomas

[Didrik Rokhaug]

Hi.

How long does it take to get the first fix, and how long does it take after the reset?

What antenna and DK version did you use?

Where was the device placed? Did it have a clear view of the sky?

How did you get the current time?

I will look more into this from my end on Monday, and will hopefully have some information to you by then (Norway time).

Best regards,

Didrik

[Thomas]

Hi Didrik,

It took around 40 seconds for both fixes using the DK 0.9.0's onboard antenna. The test was performed in a park with a clear view of the sky.

The time was from the GPS fix + RTC.

Kind regards,

Thomas

[Didrik Rokhaug]

I have looked a bit more through our internal information and talked to some of my colleagues.

The last good fix should be stored to flash when you send AT+CFUN=0 and should help with finding satellites faster.

 

Thomas said:

It took around 40 seconds for both fixes using the DK 0.9.0's onboard antenna.

 That doesn't sound very unreasonable to me. The onboard GPS antenna isn't very good on the 0.9.0 or older DKs.

You should be able to see an improvement if you use the external antenna that came with the DK. Remember to change SW2 to "CON".

 

Thomas said:

The time was from the GPS fix + RTC.

 By "RTC", do you mean Real Time Clock or Counter?

Anyway, if there are any further performance gains to be had (outside A-GPS or better antenna), I suspect it is the time estimate that is the problem.

Could you take a modem trace?

That will let me see what you are sending to the modem, and how the modem is using it.

[Thomas]

Hi Didirk,

40 seconds is reasonable for a cold fix however when I turn the GPS on and off without rebooting the system it gets a hot fix within 5 or so seconds, so I would have thought that if it saves the ephermeris to flash that a reboot of the system would provide a hot fix after providing the position and time?

I'll do a modem trace later this week (bad weather here for the next few days).

Kind regards,

Thomas