AssetTracker v2: connection management and sleep state

[ragruslan]

Hi!

I can't find a detailed technical description of the following points of the AssetTracker v2 application. Some description, explanation, details will be appreciated.

1. Connection management (connection/disconnection behavior). Does the app stay offline most of the time? Is the modem switched off during this offline periods? Or is it in some sleep mode (e.g., PSM)? What is the algorithm of connection management (including reconnections in case of a network lost)?

In the docs, I see "If the modem module receives an APP_EVT_LTE_DISCONNECT event, it instructs the modem to detach from the network". But I don't see this event to actually appear (neither in the code, nor in the logs).

2.  Power management, going to sleep. It's declared that the application sleeps most of the time. But I don't see anything clear about going to sleep neither in the app's code, nor in the logs. I would be glad to know some technical details of how it works.

Thank you!

[JONATHAN LL]

Hi,

1. Connection management (connection/disconnection behavior).

We have this section on connection in the docs: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.5.1/nrf/applications/asset_tracker_v2/doc/modem_module.html#lte-connection-handling 
Do you not feel that this addresses your question?  
Then there is also the https://developer.nordicsemi.com/nRF_Connect_SDK/doc/2.5.1/nrf/applications/asset_tracker_v2/doc/app_behavior.html behaviour section: there will be differences depending on configuration options. 

2.  Power management, going to sleep.

https://github.com/nrfconnect/sdk-nrf/blob/69b617e753df68d2be7e54cb4c204732ef137c20/include/modem/lte_lc.h#L299 there is the two handles here:

/**
	 * Modem exited from sleep.
	 *
	 * The associated payload is the @c modem_sleep member of type @ref lte_lc_modem_sleep in
	 * the event.
	 */
	LTE_LC_EVT_MODEM_SLEEP_EXIT,

	/**
	 * Modem entered sleep.
	 *
	 * The associated payload is the @c modem_sleep member of type @ref lte_lc_modem_sleep in
	 * the event. The @c time parameter indicates the duration of the sleep.
	 */
	LTE_LC_EVT_MODEM_SLEEP_ENTER,

Regards,
Jonathan

[ragruslan]

Hi Jonathan,

Thanks for the reply!

Do you not feel that this addresses your question?  

Sorry, but I don't feel so. I've seen these docs and they don't answer my questions.

LTE connection handling doc:

- (From my original question) I see "If the modem module receives an APP_EVT_LTE_DISCONNECT event, it instructs the modem to detach from the network, and a subsequent MODEM_EVT_LTE_DISCONNECTED event can be expected after the disconnect.". But I can't find this event neither in the code, nor in the logs (in both active/passive modes). Does this mean that the device stays always connected (especially if my carrier doesn't support PSM)?

- What is the reconnection policy? I see "If the network registration is lost at some point, a MODEM_EVT_LTE_DISCONNECTED event is sent.". But I see no info about reconnection. Is it handled by the LTE link control library without any calls from the application?

Application behavior and functionality doc also doesn't give any details about the connection management. I only see "In connected state?" blocks on the diagrams, nothing more about connectivity.

https://github.com/nrfconnect/sdk-nrf/blob/69b617e753df68d2be7e54cb4c204732ef137c20/include/modem/lte_lc.h#L299 there is the two handles here:

Ok, this is modem's sleep mode. As far as I understand, nRF9160 has some sleep modes/states of MCU - e.g., deep sleep. Does the AssetTracker app use some features like these?
Does it keep peripherals off (or in some low-power mode) most of the time?

Regards,
Ruslan

[Hakon]

Does the app stay offline most of the time?

What do you mean by "offline"? It can go into PSM, but that doesn't mean it is disconnected from the network.

Is the modem switched off during this offline periods?

In PSM the modem is in deep sleep mode and the antenna is turned off.

What is the algorithm of connection management (including reconnections in case of a network lost)?

The reconnection to the network is handled by the modem, but the cloud connection is handled in the cloud module.

But I don't see this event to actually appear (neither in the code, nor in the logs).

Here the event appears, and a few lines below that, the modem is turned off with lte_lc_offline().

Hope this answers your question.

[ragruslan]

Thanks for your answers!

In PSM the modem is in deep sleep mode and the antenna is turned off.

Ok. But if a carrier doesn't support PSM, what will happen? Will the device disconnect and switch off the modem (or go into flight mode)? Or will it just stay online and drain its battery quickly?

Here the event appears, and a few lines below that, the modem is turned off with lte_lc_offline().

This is a handler for this event. But I can't find this event to be emitted at all.

Also, a couple of my previous questions:

As far as I understand, nRF9160 has some sleep modes/states of MCU - e.g., deep sleep. Does the AssetTracker app use some features like these?
Does it keep peripherals off (or in some low-power mode) most of the time?