LWm2m with HL7800 modem how to get lwm2m update working correctly

[jbr-ia]

I am trying to use an HL7800 modem (on a pinnacle-100-dvk board) with LWm2m in a low-power application. I am using queue-mode, and see that (as intended) after some time the lwm2m rx-window is closed. The HL7800-modem also goes to PSM-mode. But when I try an lwm2m update (lwm2m update in the shell), than the attempt to update the registration fails and the full registration-process is starting again (this takes more time and energy than an update).

When I change the lwm2m_engine, so after it first opens a socket, sock_fd is written to 0, and again a new socket is opened, than the lwm2m update does work.
I did this by adding client_ctx->sock_fd=-1; just before lwm2m_socket_start in:

zephyr/subsys/net/lib/lwm2m/lwm2m_engine.c

Line 223 in 9e6960f

return lwm2m_socket_start(client_ctx);

With that change, the lwm2m update does work, and no full registration is needed. But this adding of sock_fd=-1 is not a correct solution. Is this probably a problem with the HL7800 driver, lwm2m-driver in zephyr, or do I have some of the timings configured wrongly?
At the moment I have the
CONFIG_LWM2M_QUEUE_MODE_UPTIME=20 (seconds)
CONFIG_MODEM_HL7800_ALLOW_SLEEP_DELAY_MS=25000 (25 seconds) and
CONFIG_MODEM_HL7800_PSM_ACTIVE_TIME="00001111" (30 seconds).
My assumption is that after the lwm2m-rx window is finished (20 seconds) a 5 seconds later the modem is allowed to hibernate, and 5 seconds after that the PSM of the modem puts the modem into low power.

Log with failed update, and fallback to full registration:

uart:~$ lwm2m update
[00:06:58.502,319] <dbg> net_lwm2m_rd_client: lwm2m_rd_client_service: State: 6
[00:06:58.502,349] <dbg> net_lwm2m_client_app: rd_client_event: Registration update
[00:06:58.502,380] <dbg> net_lwm2m_rd_client: lwm2m_rd_client_service: State: 7
[00:06:58.502,410] <dbg> net_lwm2m_engine: lwm2m_engine_connection_resume: Close and resume a new connection
[00:06:58.502,471] <dbg> modem_hl7800: allow_sleep: Keep awake
[00:06:58.502,471] <dbg> modem_hl7800: wakeup_hl7800: Waiting to wakeup
[00:06:58.503,234] <dbg> modem_hl7800: allow_sleep: Keep awake
[00:07:00.386,871] <dbg> modem_hl7800: hl7800_rx: HANDLE +KUDP_IND:  (len:3)
[00:07:00.386,932] <dbg> modem_hl7800: on_cmd_sock_ind: +KUDP_IND ID: 1
[00:07:00.387,878] <dbg> modem_hl7800: hl7800_rx: HANDLE +KSUP:  (len:1)
[00:07:00.387,939] <inf> modem_hl7800: Startup State: READY
[00:07:00.387,969] <inf> modem_hl7800: Sleep State: AWAKE
[00:07:00.388,122] <dbg> modem_hl7800: send_at_cmd: OUT: [AT+KCNXCFG=1,"GPRS","",,,"IPV4"]
[00:07:00.402,740] <dbg> modem_hl7800: hl7800_rx: HANDLE OK (len:0)
[00:07:00.402,832] <dbg> modem_hl7800: send_at_cmd: OUT: [AT+KTCPCFG?]
[00:07:00.408,691] <dbg> modem_hl7800: hl7800_rx: HANDLE OK (len:0)
[00:07:00.408,782] <dbg> modem_hl7800: send_at_cmd: OUT: [AT+KUDPCFG?]
[00:07:00.418,426] <dbg> modem_hl7800: hl7800_rx: HANDLE +KUDPCFG:  (len:23)
[00:07:00.418,487] <dbg> modem_hl7800: on_cmd_sockcreate: +KUDPCFG: 1
[00:07:00.418,945] <dbg> modem_hl7800: hl7800_rx: HANDLE OK (len:0)
[00:07:06.409,973] <err> modem_hl7800: Invalid socket_id(-1) for net_ctx:0x20005910!
[00:07:06.410,003] <err> net_lwm2m_engine: Cannot connect UDP (-22)
[00:07:06.410,095] <dbg> modem_hl7800: allow_sleep: Keep awake
[00:07:06.410,156] <dbg> modem_hl7800: send_at_cmd: OUT: [AT+KUDPCLOSE=-1]
[00:07:06.418,945] <dbg> modem_hl7800: hl7800_rx: HANDLE +CME ERROR:  (len:3)
[00:07:06.418,975] <err> modem_hl7800: Error code: 916
[00:07:12.411,651] <err> net_lwm2m_rd_client: Failed to update registration. Falling back to full registration

Log with client_ctx->sock_fd=-1; added to code:

uart:~$ lwm2m update
[00:06:36.712,432] <dbg> net_lwm2m_rd_client: lwm2m_rd_client_service: State: 6
[00:06:36.712,463] <dbg> net_lwm2m_client_app: rd_client_event: Registration update
[00:06:36.712,493] <dbg> net_lwm2m_rd_client: lwm2m_rd_client_service: State: 7
[00:06:36.712,524] <dbg> net_lwm2m_engine: lwm2m_engine_connection_resume: Close and resume a new connection
[00:06:36.712,585] <dbg> modem_hl7800: allow_sleep: Keep awake
[00:06:36.712,615] <dbg> modem_hl7800: wakeup_hl7800: Waiting to wakeup
[00:06:36.713,348] <dbg> modem_hl7800: allow_sleep: Keep awake
[00:06:38.495,178] <dbg> modem_hl7800: hl7800_rx: HANDLE +KUDP_IND:  (len:3)
[00:06:38.495,239] <dbg> modem_hl7800: on_cmd_sock_ind: +KUDP_IND ID: 1
[00:06:38.496,215] <dbg> modem_hl7800: hl7800_rx: HANDLE +KSUP:  (len:1)
[00:06:38.496,246] <inf> modem_hl7800: Startup State: READY
[00:06:38.496,276] <inf> modem_hl7800: Sleep State: AWAKE
[00:06:38.496,429] <dbg> modem_hl7800: send_at_cmd: OUT: [AT+KCNXCFG=1,"GPRS","",,,"IPV4"]
[00:06:38.510,864] <dbg> modem_hl7800: hl7800_rx: HANDLE OK (len:0)
[00:06:38.510,955] <dbg> modem_hl7800: send_at_cmd: OUT: [AT+KTCPCFG?]
[00:06:38.516,845] <dbg> modem_hl7800: hl7800_rx: HANDLE OK (len:0)
[00:06:38.516,937] <dbg> modem_hl7800: send_at_cmd: OUT: [AT+KUDPCFG?]
[00:06:38.526,580] <dbg> modem_hl7800: hl7800_rx: HANDLE +KUDPCFG:  (len:23)
[00:06:38.526,611] <dbg> modem_hl7800: on_cmd_sockcreate: +KUDPCFG: 1
[00:06:38.527,069] <dbg> modem_hl7800: hl7800_rx: HANDLE OK (len:0)
[00:06:44.518,157] <dbg> modem_hl7800: allow_sleep: Keep awake
[00:06:44.518,249] <dbg> modem_hl7800: send_at_cmd: OUT: [AT+KUDPCFG=1,0,,,,,0,1]
[00:06:44.573,760] <dbg> modem_hl7800: hl7800_rx: HANDLE +KUDPCFG:  (len:1)
[00:06:44.573,760] <dbg> modem_hl7800: on_cmd_sockcreate: +KUDPCFG: 2
[00:06:44.573,791] <dbg> modem_hl7800: on_cmd_sockcreate: look up new socket by creation id
[00:06:44.574,249] <dbg> modem_hl7800: hl7800_rx: HANDLE OK (len:0)
[00:06:44.585,144] <dbg> modem_hl7800: hl7800_rx: UNHANDLED RX
                                       2b 4b 43 4e 58 5f 49 4e  44 3a 20 31 2c 31 2c 30 |+KCNX_IN D: 1,1,0
[00:06:45.841,064] <dbg> modem_hl7800: hl7800_rx: HANDLE +KUDP_IND:  (len:3)
[00:06:45.841,094] <dbg> modem_hl7800: on_cmd_sock_ind: +KUDP_IND ID: 2
[00:06:45.841,278] <inf> net_lwm2m_engine: Connected, sock id 1
[00:06:45.841,583] <dbg> net_lwm2m_registry: lwm2m_engine_get: path:1/0/1/0, level 3, buf:0x2000c310, buflen:4
[00:06:45.841,674] <dbg> net_lwm2m_rd_client: sm_send_registration: registration sent [193.141.16.74]