net: lwm2m: Make Registration Update ahead time configurable

Allow to configure, how long before registration timeout should the
Registration Update be sent. The fixed 6 seconds used so far, might
not be enough in slower networks (like NB-IoT), resulting in frequent
re-registrations at LWM2M level.

Signed-off-by: Robert Lubos <[email protected]>

Author: rlubos

subsys/net/lib/lwm2m/Kconfig

@@ -83,6 +83,16 @@ config LWM2M_ENGINE_DEFAULT_LIFETIME
 	help
 	  Set the default lifetime (in seconds) for the LWM2M library engine
 
+config LWM2M_SECONDS_TO_UPDATE_EARLY
+	int "LWM2M Registration Update transmission time before timeout"
+	default 6
+	range 1 65535
+	help
+	  Time in seconds before the registration timeout, when the LWM2M
+	  Registration Update is sent by the engine. In networks with large
+	  round trip times (like NB-IoT), it might be needed to set this value
+	  higher, in order to allow the response to arrive before timeout.
+
 config LWM2M_QUEUE_MODE_ENABLED
 	bool "Enable Queue Mode UDP binding"
 	help

subsys/net/lib/lwm2m/lwm2m_rd_client.c

@@ -61,7 +61,7 @@ LOG_MODULE_REGISTER(LOG_MODULE_NAME);
 
 #define LWM2M_RD_CLIENT_URI "rd"
 
-#define SECONDS_TO_UPDATE_EARLY	6
+#define SECONDS_TO_UPDATE_EARLY	CONFIG_LWM2M_SECONDS_TO_UPDATE_EARLY
 #define STATE_MACHINE_UPDATE_INTERVAL_MS 500
 
 /* Leave room for 32 hexadeciaml digits (UUID) + NULL */