application: serial_lte_modem: Allow auto-connect for LwM2M

For the use case of FOTA with lwm2m_carrier,
.Enable auto-connect after FOTA image is applied.
.Enable auto-connect on all kinds of reset.
.Add AT#XCARRIER="auto-connect","read|write"[,<auto-connect-flag>]
 to control YES/NO of auto-connect.

Dependence: libmodem v2.4.2

Signed-off-by: Jun Qing Zou <jun.qing.zou@nordicsemi.no>

applications/serial_lte_modem/doc/CARRIER_AT_commands.rst

@@ -76,6 +76,7 @@ Syntax
 
 The ``<cmd>`` command is a string, and can be used as follows:
 
+* ``AT#XCARRIER="auto_connect","read|write"[,<auto-connect-flag>]``
 * ``AT#XCARRIER="app_data"[,<data>]``
 * ``AT#XCARRIER="battery_level",<battery_level>``
 * ``AT#XCARRIER="battery_status",<battery_status>``
@@ -107,6 +108,19 @@ The response syntax depends on the commands used.
 Examples
 ~~~~~~~~
 
+::
+
+   AT#XCARRIER="auto_connect","read"
+   #XCARRIER: auto_connect 1
+   OK
+
+   AT#XCARRIER="auto_connect","write",0
+   OK
+
+   AT#XCARRIER="auto_connect","read"
+   #XCARRIER: auto_connect 0
+   OK
+
 ::
 
    AT#XCARRIER="time","read"

applications/serial_lte_modem/src/lwm2m_carrier/slm_at_carrier.c

@@ -10,12 +10,15 @@
 #include <zephyr/logging/log.h>
 #include <modem/nrf_modem_lib.h>
 #include "slm_at_host.h"
+#include "slm_settings.h"
 #include "slm_util.h"
 
 LOG_MODULE_REGISTER(slm_carrier, CONFIG_SLM_LOG_LEVEL);
 
 /**@brief LwM2M Carrier operations. */
 enum slm_carrier_operation {
+	/* LTE auto-connect operation for LwM2M Carrier */
+	CARRIER_OP_AUTO_CONNECT,
 	/* Carrier AppData Operation */
 	CARRIER_OP_APPDATA_SEND,
 	/* Carrier Device Operation */
@@ -54,6 +57,7 @@ struct carrier_op_list {
 static int m_mem_free;
 
 /** forward declaration of cmd handlers **/
+static int do_carrier_auto_connect(void);
 static int do_carrier_appdata_send(void);
 static int do_carrier_device_battery_level(void);
 static int do_carrier_device_battery_status(void);
@@ -76,6 +80,7 @@ static int do_carrier_request_link_up(void);
 
 /**@brief SLM AT Command list type. */
 static struct carrier_op_list op_list[CARRIER_OP_MAX] = {
+	{CARRIER_OP_AUTO_CONNECT, "auto_connect", do_carrier_auto_connect},
 	{CARRIER_OP_APPDATA_SEND, "app_data", do_carrier_appdata_send},
 	{CARRIER_OP_DEVICE_BATTERY_LEVEL, "battery_level", do_carrier_device_battery_level},
 	{CARRIER_OP_DEVICE_BATTERY_STATUS, "battery_status", do_carrier_device_battery_status},
@@ -99,11 +104,17 @@ static struct carrier_op_list op_list[CARRIER_OP_MAX] = {
 
 #define SLM_CARRIER_OP_STR_MAX (sizeof("battery_status") + 1)
 
-/* Global variables and functions defined in different files. */
+struct k_work_delayable reconnect_work;
+
+/* Global variables defined in different files. */
+extern int32_t auto_connect;
 extern struct k_work_q slm_work_q;
 extern struct at_param_list at_param_list;
 extern uint8_t data_buf[SLM_MAX_MESSAGE_SIZE];
 
+/* Global functions defined in different files. */
+int lte_auto_connect(void);
+
 static void print_err(const lwm2m_carrier_event_t *evt)
 {
 	const lwm2m_carrier_event_error_t *err = evt->data.error;
@@ -178,15 +189,26 @@ static void on_event_app_data(const lwm2m_carrier_event_t *event)
 	data_send(data_buf, app_data->buffer_len);
 }
 
+static void reconnect_wk(struct k_work *work)
+{
+	(void)lte_auto_connect();
+}
+
 int lwm2m_carrier_event_handler(const lwm2m_carrier_event_t *event)
 {
 	int err = 0;
+	static bool fota_started;
 
 	switch (event->type) {
 	case LWM2M_CARRIER_EVENT_LTE_LINK_UP:
 		LOG_DBG("LWM2M_CARRIER_EVENT_LTE_LINK_UP");
-		/* AT+CFUN=1 to be issued. */
-		err = -1;
+		if (fota_started) {
+			fota_started = false;
+			k_work_reschedule(&reconnect_work, K_MSEC(100));
+		} else {
+			/* AT+CFUN=1 to be issued. */
+			err = -1;
+		}
 		break;
 	case LWM2M_CARRIER_EVENT_LTE_LINK_DOWN:
 		LOG_DBG("LWM2M_CARRIER_EVENT_LTE_LINK_DOWN");
@@ -209,6 +231,7 @@ int lwm2m_carrier_event_handler(const lwm2m_carrier_event_t *event)
 		break;
 	case LWM2M_CARRIER_EVENT_FOTA_START:
 		LOG_DBG("LWM2M_CARRIER_EVENT_FOTA_START");
+		fota_started = true;
 		break;
 	case LWM2M_CARRIER_EVENT_FOTA_SUCCESS:
 		LOG_DBG("LWM2M_CARRIER_EVENT_FOTA_SUCCESS");
@@ -759,6 +782,37 @@ static int do_carrier_request_link_up(void)
 	return lwm2m_carrier_request(LWM2M_CARRIER_REQUEST_LINK_UP);
 }
 
+/* AT#XCARRIER="auto_connect","read|write"[,<auto-connect-flag>] */
+static int do_carrier_auto_connect(void)
+{
+	int ret = 0;
+	int flag;
+	char operation[6];
+	size_t size = sizeof(operation);
+
+	ret = util_string_get(&at_param_list, 2, operation, &size);
+	if (ret) {
+		return ret;
+	}
+
+	if (slm_util_cmd_casecmp(operation, "READ")) {
+		rsp_send("\r\n#XCARRIER: auto_connect %d\r\n", auto_connect);
+	} else if (slm_util_cmd_casecmp(operation, "WRITE")) {
+		ret = at_params_int_get(&at_param_list, 3, &flag);
+		if (ret) {
+			return ret;
+		}
+		if (flag == 0 || flag == 1) {
+			auto_connect = flag;
+			(void)slm_settings_auto_connect_save();
+		} else {
+			ret = -EINVAL;
+		}
+	}
+
+	return ret;
+}
+
 /**@brief API to handle Carrier AT command
  */
 int handle_at_carrier(enum at_cmd_type cmd_type)
@@ -787,6 +841,8 @@ int handle_at_carrier(enum at_cmd_type cmd_type)
 
 int slm_at_carrier_init(void)
 {
+	k_work_init_delayable(&reconnect_work, reconnect_wk);
+
 	return 0;
 }
 

applications/serial_lte_modem/src/main.c

@@ -39,6 +39,9 @@ static struct k_work_delayable indicate_work;
 /* global variable used across different files */
 struct k_work_q slm_work_q;
 
+/* global variable defined in different files */
+extern int32_t auto_connect;
+
 /* global functions defined in different files */
 int poweron_uart(void);
 
@@ -47,6 +50,18 @@ static void indicate_wk(struct k_work *work);
 
 BUILD_ASSERT(CONFIG_SLM_WAKEUP_PIN >= 0, "Wake up pin not configured");
 
+NRF_MODEM_LIB_ON_INIT(lwm2m_init_hook, on_modem_lib_init, NULL);
+
+static void on_modem_lib_init(int ret, void *ctx)
+{
+	ARG_UNUSED(ctx);
+
+	/** ret: Zero on success, a positive value @em nrf_modem_dfu when executing
+	 *  Modem firmware updates, and negative errno on other failures.
+	 */
+	LOG_INF("lib_modem init: %d", ret);
+}
+
 #if defined(CONFIG_NRF_MODEM_LIB_ON_FAULT_APPLICATION_SPECIFIC)
 static void on_modem_failure_shutdown(struct k_work *item);
 static void on_modem_failure_reinit(struct k_work *item);
@@ -333,6 +348,39 @@ static void handle_mcuboot_swap_ret(void)
 	}
 }
 
+int lte_auto_connect(void)
+{
+	int err = 0;
+
+#if defined(CONFIG_SLM_CARRIER)
+	int stat;
+
+	if (!auto_connect) {
+		return 0;
+	}
+	err = nrf_modem_at_scanf("AT+CEREG?", "+CEREG: %d", &stat);
+	if (err != 1 || (stat == 1 || stat == 5)) {
+		return 0;
+	}
+
+	LOG_INF("auto connect");
+#if defined(CONFIG_LWM2M_CARRIER_SERVER_BINDING_N)
+	err = nrf_modem_at_printf("AT%%XSYSTEMMODE=0,1,0,0");
+	if (err) {
+		LOG_ERR("Failed to configure RAT: %d", err);
+		return err;
+	}
+#endif /* CONFIG_LWM2M_CARRIER_SERVER_BINDING_N */
+	err = nrf_modem_at_printf("AT+CFUN=1");
+	if (err) {
+		LOG_ERR("Failed to turn on radio: %d", err);
+		return err;
+	}
+#endif /* CONFIG_SLM_CARRIER */
+
+	return err;
+}
+
 int start_execute(void)
 {
 	int err;
@@ -351,6 +399,7 @@ int start_execute(void)
 	k_work_queue_start(&slm_work_q, slm_wq_stack_area,
 			   K_THREAD_STACK_SIZEOF(slm_wq_stack_area),
 			   SLM_WQ_PRIORITY, NULL);
+	(void)lte_auto_connect();
 
 	return 0;
 }

applications/serial_lte_modem/src/slm_settings.c

@@ -23,6 +23,8 @@ enum fota_stage fota_stage = FOTA_STAGE_INIT;		/* FOTA: stage of FOTA process */
 enum fota_status fota_status;		/* FOTA: OK/Error status */
 int32_t fota_info;		/* FOTA: failure cause in case of error or download percentage*/
 
+int32_t auto_connect = 1;	/* Auto connect network at startup or after FOTA update */
+
 bool uart_configured;		/* UART: first-time configured */
 struct uart_config slm_uart;	/* UART: config */
 
@@ -48,6 +50,11 @@ static int settings_set(const char *name, size_t len, settings_read_cb read_cb,
 			return -EINVAL;
 		if (read_cb(cb_arg, &fota_info, len) > 0)
 			return 0;
+	} else if (!strcmp(name, "auto_connect")) {
+		if (len != sizeof(auto_connect))
+			return -EINVAL;
+		if (read_cb(cb_arg, &auto_connect, len) > 0)
+			return 0;
 	} else if (!strcmp(name, "uart_configured")) {
 		if (len != sizeof(uart_configured))
 			return -EINVAL;
@@ -147,6 +154,20 @@ void slm_settings_fota_init(void)
 	fota_info = 0;
 }
 
+int slm_settings_auto_connect_save(void)
+{
+	int ret;
+
+	/* Write a single serialized value to persisted storage (if it has changed value). */
+	ret = settings_save_one("slm/auto_connect", &(auto_connect), sizeof(auto_connect));
+	if (ret) {
+		LOG_ERR("save slm/auto_connect failed: %d", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
 int slm_settings_uart_save(void)
 {
 	int ret;

applications/serial_lte_modem/src/slm_settings.h

@@ -29,6 +29,13 @@ void slm_settings_fota_init(void);
  */
 int slm_settings_fota_save(void);
 
+/**
+ * @brief Saves the auto-connect settings to NVM.
+ *
+ * @retval 0 on success, nonzero otherwise.
+ */
+int slm_settings_auto_connect_save(void);
+
 /**
  * @brief Saves the UART settings to NVM.
  *

doc/nrf/releases_and_maturity/releases/release-notes-changelog.rst

@@ -177,6 +177,8 @@ nRF9160: Serial LTE modem
   * ``#XMODEMRESET`` AT command to reset the modem while keeping the application running.
     It is expected to be used during modem firmware update, which now only requires a reset of the modem.
   * DTLS connection identifier support to the ``#XSSOCKETOPT`` and ``#XUDPCLI`` AT commands.
+  * An ``auto_connect`` operation in the ``#XCARRIER`` carrier command.
+    The operation controls automatic registration of UE to LTE network.
 
 * Updated: