Default LWM2M lifetime setting does not work

[ephimee]

I have the following:
- NRF52840
- BG96 modem
- NCS 1.5.1
- Zephyr v2.4.99-ncs2

When I start the firmware, it will first bootstrap followed by leshan server registration.

In my prj.conf I have:

CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME=900

But when I look at the tcpdump I see lt=20.

I also checked with grep:

grep -R CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME *
build_nrf52840_orbitz/zephyr/include/generated/autoconf.h:#define CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME 900
Binary file build_nrf52840/zephyr/zephyr_prebuilt.elf matches
build_nrf52840/zephyr/zephyr.lst:	lifetime[index] = CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME;
build_nrf52840/zephyr/zephyr.lst:		new_lifetime = CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME;
build_nrf52840/zephyr/zephyr.lst:		new_lifetime = CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME;
build_nrf52840/zephyr/.config.old:CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME=900
build_nrf52840/zephyr/.config:CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME=900
build_nrf52840/zephyr/misc/generated/configs.c:GEN_ABSOLUTE_SYM(CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME, 900);
Binary file build_nrf52840/zephyr/zephyr.elf matches
Binary file build_nrf52840/zephyr/libzephyr.a matches
Binary file build_nrf52840/zephyr/CMakeFiles/zephyr.dir/misc/generated/configs.c.obj matches
prj.conf:CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME=900

Somehow this setting is being overruled.
There's no mention of overrule in the documentation:
https://docs.zephyrproject.org/1.14.0/reference/kconfig/CONFIG_LWM2M_ENGINE_DEFAULT_LIFETIME.html

Also according to the documentation, the default is 30.

Where does 20 come from? and how do I change my project to use lifetime 900?

[Charlie]

Hi Philip,

nRF52840 does not support that sample. I guess you are looking for a sample like  nRF9160: LwM2M Client — nRF Connect SDK 1.8.0 documentation (nordicsemi.com)

Can you provide more information about your application?

Best regards,

Charlie

[ephimee]

I'm starting my LWM2M client with lwm2m_rd_client_start() which is located in ncs/zephyr/subsys/net/lib/lwm2m/lwm2m_rd_client.c

The application is basically polling the BG96 modem for GPS coordinates and send it via LWM2M object 3336/0/5514 and 3336/0/5515

Stack trace I have up until now:

Modem_AddEventCallback(ModemObserverCallback)
    ModemObserverCallback()
        StartLwM2MClient()
            LwM2M_ClientStart()
                lwm2m_rd_client_start()
                    set_sm_state(ENGINE_INIT);
		                case ENGINE_INIT:
                             sm_do_init();
                                   client.lifetime = 0U;

In the beginning the lifetime is set to 0. Later on it's set to the correct value.

I've narrowed it down to the function:

static int lwm2m_engine_get(char *pathstr, void *buf, uint16_t buflen)

There it uses this function:

path_to_objs()

To convert the path into an object with the lifetime in it, but I do not understand the code or where the lifetime comes from?

If I look at the function:

static int path_to_objs(const struct lwm2m_obj_path *path,
			struct lwm2m_engine_obj_inst **obj_inst,
			struct lwm2m_engine_obj_field **obj_field,
			struct lwm2m_engine_res **res,
			struct lwm2m_engine_res_inst **res_inst)
{

It somehow gets this information from the objects.

I also thought maybe the lifetime is set using the function:

lwm2m_engine_set()

But when I look at the logging I get:

[00:00:06.484,893] <dbg> net_lwm2m_engine.lwm2m_engine_set: path:0/0/2, value:0x2001a837, len:1
[00:00:06.484,954] <dbg> net_lwm2m_engine.lwm2m_engine_set: path:0/0/3, value:0x20012662, len:2
[00:00:06.484,985] <dbg> net_lwm2m_engine.lwm2m_engine_set: path:0/0/5, value:0x200126a2, len:5
[00:00:06.485,046] <dbg> net_lwm2m_engine.lwm2m_engine_set: path:0/0/1, value:0x2001a837, len:1
[00:00:19.959,045] <dbg> net_lwm2m_engine.lwm2m_engine_get: path:0/0/1, buf:0x20018c57, buflen:1
[00:03:35.387,329] <dbg> net_lwm2m_engine.lwm2m_engine_get: path:0/0/1, buf:0x20018c57, buflen:1
[00:03:43.638,336] <dbg> net_lwm2m_engine.lwm2m_engine_get: path:0/0/1, buf:0x20018c57, buflen:1
[00:03:43.638,397] <dbg> net_lwm2m_engine.lwm2m_engine_get: path:0/1/1, buf:0x20018c57, buflen:1
[00:03:43.638,458] <dbg> net_lwm2m_engine.lwm2m_engine_get: path:0/1/10, buf:0x20018caa, buflen:2

I do not see object 1/0/1, which is lifetime.

I am able to set lifetime from lwm2m server web GUI. So when lifetime is only 20 seconds, I quickly set it higher via the lwm2m server web GUI.

[Charlie]

Hi Philip,

ephimee said:

BG96 modem for GPS coordinates and send it via LWM2M

so what is nRF52840 used for on your application? It does not support running as an LWM2M client.

Best regards,

Charlie

[ephimee]

The nRF52840 is mainly used as LWM2M client to connect sensors/actuators on one side and a IOT modem on the other side. The business logic processes the information between all components.

I do not understand why LWM2M is not supported? It's available in SDK16, which we use for our customers. Because SDK16 is getting outdated, you recommended going to Zephyr.

[Charlie]

Hi Philip,

I think you are referring to this experimental sample: https://infocenter.nordicsemi.com/topic/sdk_nrf5_v16.0.0/iot_sdk_app_lwm2m_client.html. As far as I know, it never reaches the production level from that time.

We did not have a similar solution after switching to NCS. Instead, we offer some other replacement solutions considering performance, technical trends in this field, our product line, and so on. You can have a look at the following sample which may be the proper choice for your current application.

nRF9160: LwM2M Client — nRF Connect SDK 1.8.0 documentation (nordicsemi.com)

Matter samples — nRF Connect SDK 1.8.0 documentation (nordicsemi.com)

Best regards,

Charlie