LTE Link connecting is blocking?

[ExAg]

Hi

In the mqtt_simple example there is a line "modem_configure();" which establishes the LTE Link connection. If connecting the LTE link is not possible (for example no signal), this function never returns.

1. Is this the intention of this function or is there a possibility to configure a timeout?

2. Is it normal, that this function needs several minutes to establish the LTE link, if a provider is present?

regards

ExAg

[Simon]

1. Is this the intention of this function or is there a possibility to configure a timeout?

The reason it is blocking is due to some semaphores inside w_lte_lc_init_and_connect(..) in lte_lc.c. It will wait for the at_handler() to run and if the response is appropriate it will give up the semaphore and the program continues. See code below

//From w_lte_lc_init_and_connect() in lte_lc.c

k_sem_init(&link, 0, 1);
        //k_sem_init(&link, 1, 2);

	at_cmd_set_notification_handler(at_handler);

	if (at_cmd_write(normal, NULL, 0, NULL) != 0) {
		return -EIO;
	}

	k_sem_take(&link, K_FOREVER);

You can set a timeout, by running k_sem_take(&link, timeout_in_ms); where you specify the timeout in timeout_in_ms. 

Be aware that this may cause some unwanted results/race conditions etc., but I am not sure specifically what may happen.

 

2. Is it normal, that this function needs several minutes to establish the LTE link, if a provider is present?

 I will look into this and come back to you.

Best regards,

Simon

[Simon]

ExAg said:

2. Is it normal, that this function needs several minutes to establish the LTE link, if a provider is present?

The time to establish an LTE link varies depending on the signal strength and the network, it may more than 5 minutes at worst. If the network settings are stored on the modem, the connection only takes some few seconds. The network settings are automatically stored to the modem when the modem is turned off, through the call to AT+CFUN=0.

Best regards,

Simon

[ExAg]

Hi Simon

Thank you very much for the reply. I don't know if I understand your answer correctly. My problem is during debugging of C-code. If I stopp the debugger and than start a new debug session, I allways have to wait (blocking) at least 1:30 minutes up to more than 6 minutes until I have a LTE Link.

How exaclty can I speed up this LTE connection time? What do you mean with AT+CFUN=0?

Regards

ExAg

[Yusuke]

In my case, when I restrict bands, connection time is shortened. 

AT%XBANDLOCK=1,"10000000" // only band 8

iBasis collects bands and chooses the strongest band. So I guess restricting bands reduce the collecting time.

[ExAg]

Hi Yusuke

Thank you for this tip. Unfortunatly for me, this is not really a solution because i do not know, which bands are aviable in all the locations where we want to deliver our devices.

But probably during development, this could speed up the connection a little bit...

[ExAg]

Hi Simon

Here are my latest observations according the modem connection time:
I have updated the modem firmware to 1.0.1.
It seems, that the connection time is much faster, if the eval-kit is runnig without debugger. After pushing reset, it takes about 5s to (re)connect the LTE link.
But if I use the debugger, it takes this 1:30 to 6 minutes to connect...

Are there any settings or configurations I have to set up for faster debugging?
(The CONFIG_DEBUG_OPTIMIZATIONS=y is allready set in prj.conf).

Regards
ExAg

[Simon]

Just to make things clear. You are talking about the time between here and here? 

I am not able to reprocuce your behaviour. What NCS tag are you using? Are you using the mqtt_simple example as it is or have you done any changes? 

Best regards,

Simon