Modem cellular reconnect algorithm

[davidk88]

Hello,

How to react on NET_EVENT_L4_DISCONNECTED event with cellular modem to restore connectivity? Should I call net_if_down() and net_if_up()? In that case I cannot get socket to connect again, it is returning error 22 and warnings like:

net_ctx: DROP: src addr is unspecified

It only helps if I suspend / resume modem.

Best regards

[davidk88]

Hello,

so now I just want to pm suspend and then pm resume modem after I get NET_EVENT_L4_DISCONNECTED:

[00:07:29.597,000] conn_mgr: conn_mgr_ipv4_events_handler: (0x2000bb50): IPv4 event 0xe030000000000002 received on iface 1 (0x20002ee0)
[00:07:29.597,000] conn_mgr: conn_mgr_ipv4_events_handler: (0x2000bb50): Iface index 0
[00:07:29.597,000] m_conn: event_handler: Network disconnected event
[00:07:29.597,000] net_ctx: net_context_unref: (0x20002fb8): Context 0x2000bbf8 released
[00:07:29.647,000] m_conn: conn_thread: L4 reconnect procedure!
[00:07:29.647,000] conn_mgr: conn_mgr_iface_events_handler: (0x2000bb50): Iface event 0xd010000000000001 received on iface 1 (0x20002ee0)
[00:07:29.647,000] conn_mgr: conn_mgr_iface_events_handler: (0x2000bb50): Iface index 0
Here i suspend and the resume modem:
[00:07:31.683,000] m_conn: conn_thread: modem suspend: 0
[00:07:36.683,000] m_conn: conn_thread: modem resume: 0

[00:07:50.709,000] conn_mgr: conn_mgr_iface_events_handler: (0x2000bb50): Iface event 0xd010000000000002 received on iface 1 (0x20002ee0)
[00:07:50.709,000] conn_mgr: conn_mgr_iface_events_handler: (0x2000bb50): Iface index 0
[00:07:50.709,000] net_l2_ppp: ppp_change_phase_debug: (0x2000bb50): [0x2000c278] phase DEAD (0) => ES
TABLISH (1) (ppp_open_async():221)
[00:07:50.709,000] net_l2_ppp: ppp_open_async: (0x2000bb50): Starting LCP
[00:07:50.709,000] net_l2_ppp: ppp_fsm_lower_up: (0x2000bb50): [LCP/0x2000c2b0] Current state STOPPED (3)
[00:07:50.709,000] net_l2_ppp: ppp_fsm_lower_up: (0x2000bb50): [LCP/0x2000c2b0] Invalid state STOPPED (3)
[00:07:50.709,000] net_l2_ppp: ppp_fsm_open: (0x2000bb50): [LCP/0x2000c2b0] Current state STOPPED (3)

and here everything stops.

"net iface" command from shell reports ipv4 none
Also command from shell: "net iface down 1" returns: Cannot take interface 1 down (-11)

I can regain connectivity only if I do suspend and resume modem again at this point.

[davidk88]

It helps if I chnage line fsm->flags = 0U to fsm->flags = FSM_RESTART in ppp_fsm_init (zephyr/subsys/net/l2/fsm.c). I'm using latest zephyr (main branch).

if flags are 0 as originally set, then in ppp_fsm_open function if state is PPP_STOPPED nothing happens:

case PPP_STOPPED:
	if (fsm->flags & FSM_RESTART) {
		ppp_fsm_lower_down(fsm);
		ppp_fsm_lower_up(fsm);
	}

Should I open a issue?

Similiar problem:
#75603