it seems that GPS data is getting deleted when sending nRF to sleep with AT#XSLEEP=1 command + AGPS issue

Question

Hi, 
 
 I'm using nRF9160 SLM application SDK 1.9.1 
 We are using the GPS in 4 operation modes and in between we sent nRF to sleep, it seems when we sent it to sleep all the GPS data is lost and every time we want to get a fix we get it by cold start (60 to 120 seconds to get a fix) and not hot start (few seconds to get a fix)- we use 1/5/15/30 minutes intervals atm 
 If I do CFUN=0, come after 20 minutes, do CFUN=31 and look for GPS I get a fix in about 5 seconds If I do SLEEP=1, wake up after 10 seconds, do CFUN=31 and look for GPS I get a fix in about 60-120 seconds (like the first fix from the cold start) 
 How can I overcome this issue and get a hot fix after going to SLEEP? 
 
 We are also using AGPS every 4 hours to have data refresh so we can get fixes faster (doesn't really help since we go to sleep and all the data is lost) - after an AGPS request from the cloud there is 1 minute timeout for the modem to go idle and then it starts to look for GPS (which take 60-120 second to get a fix even with the data - why? it suppose to be much faster) - how can I reduce this 60 second and make the modem go idle faster? 
 *I think the reason it takes AGPS similar time to get a fix like normal GPS is because of this : 
 "Received":{3 items
"appId":"AGPS"
"messageType":"DATA"
"data":{6 items
"mcc":425
"mnc":1
"tac":19411
"eci":16386561
"rsrp":-140
"types":[8 items
0:1
1:2
2:3
3:4
4:6
5:7
6:8
7:9
]
}
}
"ERROR":{1 item
"message":"src property must be a valid json object"
}
"ERROR":{1 item
"message":"src property must be a valid json object"
} 
 Why this error occur? 
 
 Thanks, 
 Ofir

JONATHAN LL · Accepted Answer

Update:

Pleas see the documentation of the XSLEEP, using XSLEEP=1 does disable both UART, SLM service and the modem. Setting it two 2 instead only disables UART, and when the app-core/modem is not doing anything then it idles.

So test with =2 and see if that solves the issue you have.

Regards,
Jonathan

JONATHAN LL · Answer

Every time the modem is turned off it will loos its timing, so then it will use more time to get a GPS fix. RAM retention will not be solution here as it is not the RAM in the modem that would be retained. Modem trace: https://infocenter.nordicsemi.com/topic/ug_trace_collector/UG/trace_collector/intro.html?cp=10_3_3 If you could share what you do well as the modem trace then we might be able to better address the challenges you are seeing. Can you share what you are trying to do and how you plan to use the nrf9160 and its features? How often do you plan to get a GPS fix? How important is power consumption? 
 Ofir_A said: After I receive the AGPS data from the cloud how can I send modem to idle? (he goes to idle after 60 seconds and I want it to be less) 
 This can depend on the network, so idling will happen when PSM\eDRX is granted, and that is up to the network to decide. Regards, Jonathan

JONATHAN LL · Answer

To how often the AGPS data is needed: 
 GNSS requests new A-GPS data when it's needed. There's different assistance data with different validity times. Ephemerides have the shortest validity time, they are only valid for 2 hours on average. So, to always have fresh assistance data available, GNSS should request new data roughly every two hours. You don't have to always download everything, but GNSS tells which data is needed. Usually it's only the ephemerides. For example almanacs are valid for weeks. Ofir_A said: Is there a way to give GPS priority with the SLM application? 
 No, the modem will prioritise LTE over GPS 
Regards, Jonathan

it seems that GPS data is getting deleted when sending nRF to sleep with AT#XSLEEP=1 command + AGPS issue

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