Using modem/nrf_modem_lib.h and modem/lte_lc.h

[Fridtjof]

Hello dear Nordic support staff,

I'm working on some legacy code (NCS 1.8.0 in case it's relevant) and see this in the inclusion list of one of the files:

#include <modem/nrf_modem_lib.h>
#include <modem/lte_lc.h>

Functions from both libraries are used to set up the modem and create a connection. I'm new to network code on the nrf9160, but looking at samples and documentation, it seems like using only one of the libraries is enough, where you choose lte_lc if you want more granular control.

E.g, the udp sample uses only lte_lc.h, while the http_update sample uses only nrf_modem_lib.h. I also see that the modem_shell sample uses both. Why?

[Fridtjof]

To illustrate the difference, here are the steps that the udp, modem_shell and http_update samples use to connect. I have reduced the code to only what seems like relevant function calls, and added comments

// Sample UDP

lte_lc_init();
// [Configure low power settings]
lte_lc_connect_async(lte_handler);
// [Wait for lte_handler to give a semaphore before continuing]
// [Do actual network stuff using net/socket.h]

// Sample HTTP Update
nrf_modem_lib_init(NORMAL_MODE);
fota_download_init(fota_dl_handler);
// [optional cert provisioning]
lte_lc_init_and_connect();
fota_download_start();

// Sample Modem Shell
nrf_modem_lib_init(NORMAL_MODE);
at_cmd_init();
at_notif_init();
at_monitor_init();
lte_lc_init();

I just don't see when it is necessary to initialize the modem with one library or the other. Upon closer inspection it seems http_update also uses the lc_lte library in common/include/update.c.

[Hakon]

Hello,

Functions from both libraries are used to set up the modem and create a connection. I'm new to network code on the nrf9160, but looking at samples and documentation, it seems like using only one of the libraries is enough, where you choose lte_lc if you want more granular control.

I think it should be the other way around, modem library is for more granular control. lte_lc library uses the modem library for setting up and handling LTE connection, including setting PSM and EDRX. If you want full control you should rather use the modem library. Then you will also be able to send AT commands directly to the modem. The lte_lc library is mostly for convenience as far as I know.

[Fridtjof]

I see. Thank you for the clarification, Håkon!