Lightweight M2M (LWM2M)¶

Overview
Example LwM2M object and resources: Device
Sample usage
Using LwM2M library with DTLS
API Reference

Overview ¶

Lightweight Machine to Machine (LwM2M) is an application layer protocol designed with device management, data reporting and device actuation in mind. Based on CoAP/UDP, LwM2M is a standard defined by the Open Mobile Alliance and suitable for constrained devices by its use of CoAP packet-size optimization and a simple, stateless flow that supports a REST API.

One of the key differences between LwM2M and CoAP is that an LwM2M client initiates the connection to an LwM2M server. The server can then use the REST API to manage various interfaces with the client.

LwM2M uses a simple resource model with the core set of objects and resources defined in the specification.

Example LwM2M object and resources: Device ¶

Object definition

Object ID	Name	Instance	Mandatory
3	Device	Single	Mandatory

Resource definitions

* R=Read, W=Write, E=Execute

ID	Name	OP*	Instance	Mandatory	Type
0	Manufacturer	R	Single	Optional	String
1	Model	R	Single	Optional	String
2	Serial number	R	Single	Optional	String
3	Firmware version	R	Single	Optional	String
4	Reboot	E	Single	Mandatory
5	Factory Reset	E	Single	Optional
6	Available Power Sources	R	Multiple	Optional	Integer 0-7
7	Power Source Voltage (mV)	R	Multiple	Optional	Integer
8	Power Source Current (mA)	R	Multiple	Optional	Integer
9	Battery Level %	R	Single	Optional	Integer
10	Memory Free (Kb)	R	Single	Optional	Integer
11	Error Code	R	Multiple	Optional	Integer 0-8
12	Reset Error	E	Single	Optional
13	Current Time	RW	Single	Optional	Time
14	UTC Offset	RW	Single	Optional	String
15	Timezone	RW	Single	Optional	String
16	Supported Binding	R	Single	Mandatory	String
17	Device Type	R	Single	Optional	String
18	Hardware Version	R	Single	Optional	String
19	Software Version	R	Single	Optional	String
20	Battery Status	R	Single	Optional	Integer 0-6
21	Memory Total (Kb)	R	Single	Optional	Integer
22	ExtDevInfo	R	Multiple	Optional	ObjLnk

The server could query the Manufacturer resource for Device object instance 0 (the default and only instance) by sending a READ 3/0/0 operation to the client.

The full list of registered objects and resource IDs can be found in the LwM2M registry.

Zephyr’s LwM2M library lives in the subsys/net/lib/lwm2m, with a client sample in samples/net/lwm2m_client. For more information about the provided sample see: LwM2M client The sample can be configured to use normal unsecure network sockets or sockets secured via DTLS.

The Zephyr LwM2M library implements the following items:

engine to process networking events and core functions
RD client which performs BOOTSTRAP and REGISTRATION functions
TLV, JSON, and plain text formatting functions
LwM2M Technical Specification Enabler objects such as Security, Server, Device, Firmware Update, etc.
Extended IPSO objects such as Light Control, Temperature Sensor, and Timer

The library currently implements up to LwM2M specification 1.0.2.

For more information about LwM2M visit OMA Specworks LwM2M.

Sample usage ¶

To use the LwM2M library, start by creating an LwM2M client context lwm2m_ctx structure:

/* LwM2M client context */
static struct lwm2m_ctx client;

Create callback functions for LwM2M resource exuctions:

static int device_reboot_cb(uint16_t obj_inst_id, uint8_t *args,
                            uint16_t args_len)
{
        LOG_INF("Device rebooting.");
        LOG_PANIC();
        sys_reboot(0);
        return 0; /* wont reach this */
}

The LwM2M RD client can send events back to the sample. To receive those events, setup a callback function:

static void rd_client_event(struct lwm2m_ctx *client,
                            enum lwm2m_rd_client_event client_event)
{
        switch (client_event) {

        case LWM2M_RD_CLIENT_EVENT_NONE:
                /* do nothing */
                break;

        case LWM2M_RD_CLIENT_EVENT_BOOTSTRAP_REG_FAILURE:
                LOG_DBG("Bootstrap registration failure!");
                break;

        case LWM2M_RD_CLIENT_EVENT_BOOTSTRAP_REG_COMPLETE:
                LOG_DBG("Bootstrap registration complete");
                break;

        case LWM2M_RD_CLIENT_EVENT_BOOTSTRAP_TRANSFER_COMPLETE:
                LOG_DBG("Bootstrap transfer complete");
                break;

        case LWM2M_RD_CLIENT_EVENT_REGISTRATION_FAILURE:
                LOG_DBG("Registration failure!");
                break;

        case LWM2M_RD_CLIENT_EVENT_REGISTRATION_COMPLETE:
                LOG_DBG("Registration complete");
                break;

        case LWM2M_RD_CLIENT_EVENT_REG_UPDATE_FAILURE:
                LOG_DBG("Registration update failure!");
                break;

        case LWM2M_RD_CLIENT_EVENT_REG_UPDATE_COMPLETE:
                LOG_DBG("Registration update complete");
                break;

        case LWM2M_RD_CLIENT_EVENT_DEREGISTER_FAILURE:
                LOG_DBG("Deregister failure!");
                break;

        case LWM2M_RD_CLIENT_EVENT_DISCONNECT:
                LOG_DBG("Disconnected");
                break;

        }
}

Next we assign Security resource values to let the client know where and how to connect as well as set the Manufacturer and Reboot resources in the Device object with some data and the callback we defined above:

/*
 * Server URL of default Security object = 0/0/0
 * Use leshan.eclipse.org server IP (5.39.83.206) for connection
 */
lwm2m_engine_set_string("0/0/0", "coap://5.39.83.206");

/*
 * Security Mode of default Security object = 0/0/2
 * 3 = NoSec mode (no security beware!)
 */
lwm2m_engine_set_u8("0/0/2", 3);

#define CLIENT_MANUFACTURER "Zephyr Manufacturer"

/*
 * Manufacturer resource of Device object = 3/0/0
 * We use lwm2m_engine_set_res_data() function to set a pointer to the
 * CLIENT_MANUFACTURER string.
 * Note the LWM2M_RES_DATA_FLAG_RO flag which stops the engine from
 * trying to assign a new value to the buffer.
 */
lwm2m_engine_set_res_data("3/0/0", CLIENT_MANUFACTURER,
                          sizeof(CLIENT_MANUFACTURER),
                          LWM2M_RES_DATA_FLAG_RO);

/* Reboot resource of Device object = 3/0/4 */
lwm2m_engine_register_exec_callback("3/0/4", device_reboot_cb);

Lastly, we start the LwM2M RD client (which in turn starts the LwM2M engine). The second parameter of lwm2m_rd_client_start() is the client endpoint name. This is important as it needs to be unique per LwM2M server:

(void)memset(&client, 0x0, sizeof(client));
lwm2m_rd_client_start(&client, "unique-endpoint-name", 0, rd_client_event);

Using LwM2M library with DTLS ¶

The Zephyr LwM2M library can be used with DTLS transport for secure communication by selecting CONFIG_LWM2M_DTLS_SUPPORT. In the client initialization we need to create a PSK and identity. These need to match the security information loaded onto the LwM2M server. Normally, the endpoint name is used to lookup the related security information:

/* "000102030405060708090a0b0c0d0e0f" */
static unsigned char client_psk[] = {
        0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
        0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f
};

static const char client_identity[] = "Client_identity";

Next we alter the Security object resources to include DTLS security information. The server URL should begin with coaps:// to indicate security is required. Assign a 0 value (Pre-shared Key mode) to the Security Mode resource. Lastly, set the client identity and PSK resources.

/* Use coaps:// for server URL protocol */
lwm2m_engine_set_string("0/0/0", "coaps://5.39.83.206");
/* 0 = Pre-Shared Key mode */
lwm2m_engine_set_u8("0/0/2", 0);
/* Set the client identity */
lwm2m_engine_set_string("0/0/3", (char *)client_identity);
/* Set the client pre-shared key (PSK) */
lwm2m_engine_set_opaque("0/0/5", (void *)client_psk, sizeof(client_psk));

Before calling lwm2m_rd_client_start() assign the tls_tag # where the LwM2M library should store the DTLS information prior to connection (normally a value of 1 is ok here).

(void)memset(&client, 0x0, sizeof(client));
client.tls_tag = 1; /* <---- */
lwm2m_rd_client_start(&client, "endpoint-name", 0, rd_client_event);

For a more detailed LwM2M client sample see: LwM2M client.

API Reference ¶

group lwm2m_api

LwM2M high-level API.

LwM2M high-level interface is defined in this header.

Note: The implementation assumes UDP module is enabled.
Note: LwM2M 1.0.x is currently the only supported version.

Defines

LWM2M_OBJECT_SECURITY_ID¶: LwM2M Objects managed by OMA for LwM2M tech specification. Objects in this range have IDs from 0 to 1023. For more information refer to Technical Specification OMA-TS-LightweightM2M-V1_0_2-20180209-A.

LWM2M_OBJECT_SERVER_ID¶

LWM2M_OBJECT_ACCESS_CONTROL_ID¶

LWM2M_OBJECT_DEVICE_ID¶

LWM2M_OBJECT_CONNECTIVITY_MONITORING_ID¶

LWM2M_OBJECT_FIRMWARE_ID¶

LWM2M_OBJECT_LOCATION_ID¶

LWM2M_OBJECT_CONNECTIVITY_STATISTICS_ID¶

IPSO_OBJECT_GENERIC_SENSOR_ID¶: LwM2M Objects produced by 3rd party Standards Development Organizations. Objects in this range have IDs from 2048 to 10240 Refer to the OMA LightweightM2M (LwM2M) Object and Resource Registry: http://www.openmobilealliance.org/wp/OMNA/LwM2M/LwM2MRegistry.html.

IPSO_OBJECT_TEMP_SENSOR_ID¶

IPSO_OBJECT_HUMIDITY_SENSOR_ID¶

IPSO_OBJECT_LIGHT_CONTROL_ID¶

IPSO_OBJECT_ACCELEROMETER_ID¶

IPSO_OBJECT_PRESSURE_ID¶

IPSO_OBJECT_BUZZER_ID¶

IPSO_OBJECT_TIMER_ID¶

IPSO_OBJECT_ONOFF_SWITCH_ID¶

IPSO_OBJECT_PUSH_BUTTON_ID¶

LWM2M_DEVICE_PWR_SRC_TYPE_DC_POWER¶: Power source types used for the “Available Power Sources” resource of the LwM2M Device object.

LWM2M_DEVICE_PWR_SRC_TYPE_BAT_INT¶

LWM2M_DEVICE_PWR_SRC_TYPE_BAT_EXT¶

LWM2M_DEVICE_PWR_SRC_TYPE_UNUSED¶

LWM2M_DEVICE_PWR_SRC_TYPE_PWR_OVER_ETH¶

LWM2M_DEVICE_PWR_SRC_TYPE_USB¶

LWM2M_DEVICE_PWR_SRC_TYPE_AC_POWER¶

LWM2M_DEVICE_PWR_SRC_TYPE_SOLAR¶

LWM2M_DEVICE_PWR_SRC_TYPE_MAX¶

LWM2M_DEVICE_ERROR_NONE¶: Error codes used for the “Error Code” resource of the LwM2M Device object. An LwM2M client can register one of the following error codes via the lwm2m_device_add_err() function.

LWM2M_DEVICE_ERROR_LOW_POWER¶

LWM2M_DEVICE_ERROR_EXT_POWER_SUPPLY_OFF¶

LWM2M_DEVICE_ERROR_GPS_FAILURE¶

LWM2M_DEVICE_ERROR_LOW_SIGNAL_STRENGTH¶

LWM2M_DEVICE_ERROR_OUT_OF_MEMORY¶

LWM2M_DEVICE_ERROR_SMS_FAILURE¶

LWM2M_DEVICE_ERROR_NETWORK_FAILURE¶

LWM2M_DEVICE_ERROR_PERIPHERAL_FAILURE¶

LWM2M_DEVICE_BATTERY_STATUS_NORMAL¶: Battery status codes used for the “Battery Status” resource (3/0/20) of the LwM2M Device object. As the battery status changes, an LwM2M client can set one of the following codes via: lwm2m_engine_set_u8(“3/0/20”, [battery status])

LWM2M_DEVICE_BATTERY_STATUS_CHARGING¶

LWM2M_DEVICE_BATTERY_STATUS_CHARGE_COMP¶

LWM2M_DEVICE_BATTERY_STATUS_DAMAGED¶

LWM2M_DEVICE_BATTERY_STATUS_LOW¶

LWM2M_DEVICE_BATTERY_STATUS_NOT_INST¶

LWM2M_DEVICE_BATTERY_STATUS_UNKNOWN¶

STATE_IDLE¶

LWM2M Firmware Update object states.

An LwM2M client or the LwM2M Firmware Update object use the following codes to represent the LwM2M Firmware Update state (5/0/3).

STATE_DOWNLOADING¶

STATE_DOWNLOADED¶

STATE_UPDATING¶

RESULT_DEFAULT¶

LWM2M Firmware Update object result codes.

After processing a firmware update, the client sets the result via one of the following codes via lwm2m_engine_set_u8(“5/0/5”, [result code])

RESULT_SUCCESS¶

RESULT_NO_STORAGE¶

RESULT_OUT_OF_MEM¶

RESULT_CONNECTION_LOST¶

RESULT_INTEGRITY_FAILED¶

RESULT_UNSUP_FW¶

RESULT_INVALID_URI¶

RESULT_UPDATE_FAILED¶

RESULT_UNSUP_PROTO¶

LWM2M_FLOAT32_DEC_MAX¶

Data structure used to represent the LwM2M float type: val1 is the whole number portion of the decimal val2 is the decimal portion *1000000 for 32bit, *1000000000 for 64bit Example: 123.456 == val1: 123, val2:456000 Example: 123.000456 = val1: 123, val2:456.

Maximum precision value for 32-bit LwM2M float val2

LWM2M_FLOAT64_DEC_MAX¶: Maximum precision value for 64-bit LwM2M float val2.

LWM2M_OBJLNK_MAX_ID¶: Maximum value for ObjLnk resource fields.

LWM2M_RES_DATA_READ_ONLY¶: Resource read-only value bit.

LWM2M_RES_DATA_FLAG_RO¶: Resource read-only flag.

LWM2M_HAS_RES_FLAG(res, f)¶: Read resource flags helper macro.

LWM2M_RD_CLIENT_FLAG_BOOTSTRAP¶: Run bootstrap procedure in current session.

Typedefs

typedef void (*lwm2m_socket_fault_cb_t)(int error)¶

typedef void *(*lwm2m_engine_get_data_cb_t)(uint16_t obj_inst_id, uint16_t res_id, uint16_t res_inst_id, size_t *data_len)¶

Asynchronous callback to get a resource buffer and length.

Prior to accessing the data buffer of a resource, the engine can use this callback to get the buffer pointer and length instead of using the resource’s data buffer.

The client or LwM2M objects can register a function of this type via: lwm2m_engine_register_read_callback() lwm2m_engine_register_pre_write_callback()

Return

Callback returns a pointer to the data buffer or NULL for failure.

Parameters

[in] obj_inst_id: Object instance ID generating the callback.
[in] res_id: Resource ID generating the callback.
[in] res_inst_id: Resource instance ID generating the callback (typically 0 for non-multi instance resources).
[out] data_len: Length of the data buffer.

typedef int (*lwm2m_engine_set_data_cb_t)(uint16_t obj_inst_id, uint16_t res_id, uint16_t res_inst_id, uint8_t *data, uint16_t data_len, bool last_block, size_t total_size)¶

Asynchronous callback when data has been set to a resource buffer.

After changing the data of a resource buffer, the LwM2M engine can make use of this callback to pass the data back to the client or LwM2M objects.

A function of this type can be registered via: lwm2m_engine_register_post_write_callback()

Return

Callback returns a negative error code (errno.h) indicating reason of failure or 0 for success.

Parameters

[in] obj_inst_id: Object instance ID generating the callback.
[in] res_id: Resource ID generating the callback.
[in] res_inst_id: Resource instance ID generating the callback (typically 0 for non-multi instance resources).
[in] data: Pointer to data.
[in] data_len: Length of the data.
[in] last_block: Flag used during block transfer to indicate the last block of data. For non-block transfers this is always false.
[in] total_size: Expected total size of data for a block transfer. For non-block transfers this is 0.

typedef int (*lwm2m_engine_user_cb_t)(uint16_t obj_inst_id)¶

Asynchronous event notification callback.

Various object instance and resource-based events in the LwM2M engine can trigger a callback of this function type: object instance create, and object instance delete.

Register a function of this type via: lwm2m_engine_register_create_callback() lwm2m_engine_register_delete_callback()

Return

Callback returns a negative error code (errno.h) indicating reason of failure or 0 for success.

Parameters

[in] obj_inst_id: Object instance ID generating the callback.

typedef int (*lwm2m_engine_execute_cb_t)(uint16_t obj_inst_id, uint8_t *args, uint16_t args_len)¶

Asynchronous execute notification callback.

Resource executes trigger a callback of this type.

Register a function of this type via: lwm2m_engine_register_exec_callback()

Return

Callback returns a negative error code (errno.h) indicating reason of failure or 0 for success.

Parameters

[in] obj_inst_id: Object instance ID generating the callback.
[in] args: Pointer to execute arguments payload. (This can be NULL if no arguments are provided)
[in] args_len: Length of argument payload in bytes.

typedef struct float32_value float32_value_t¶: 32-bit variant of the LwM2M float structure

typedef struct float64_value float64_value_t¶: 32-bit variant of the LwM2M float structure

typedef void (*lwm2m_ctx_event_cb_t)(struct lwm2m_ctx *ctx, enum lwm2m_rd_client_event event)¶

Asynchronous RD client event callback.

Parameters

[in] ctx: LwM2M context generating the event
[in] event: LwM2M RD client event code

Enums

enum lwm2m_rd_client_event¶

LwM2M RD client events.

LwM2M client events are passed back to the event_cb function in lwm2m_rd_client_start()

Values:

enumerator LWM2M_RD_CLIENT_EVENT_NONE¶

enumerator LWM2M_RD_CLIENT_EVENT_BOOTSTRAP_REG_FAILURE¶

enumerator LWM2M_RD_CLIENT_EVENT_BOOTSTRAP_REG_COMPLETE¶

enumerator LWM2M_RD_CLIENT_EVENT_BOOTSTRAP_TRANSFER_COMPLETE¶

enumerator LWM2M_RD_CLIENT_EVENT_REGISTRATION_FAILURE¶

enumerator LWM2M_RD_CLIENT_EVENT_REGISTRATION_COMPLETE¶

enumerator LWM2M_RD_CLIENT_EVENT_REG_UPDATE_FAILURE¶

enumerator LWM2M_RD_CLIENT_EVENT_REG_UPDATE_COMPLETE¶

enumerator LWM2M_RD_CLIENT_EVENT_DEREGISTER_FAILURE¶

enumerator LWM2M_RD_CLIENT_EVENT_DISCONNECT¶

enumerator LWM2M_RD_CLIENT_EVENT_QUEUE_MODE_RX_OFF¶

enumerator LWM2M_RD_CLIENT_EVENT_NETWORK_ERROR¶

Functions

int lwm2m_device_add_err(uint8_t error_code)¶

Register a new error code with LwM2M Device object.

Return

0 for success or negative in case of error.

Parameters

[in] error_code: New error code.

int lwm2m_engine_create_obj_inst(char *pathstr)¶

Create an LwM2M object instance.

LwM2M clients use this function to create non-default LwM2M objects: Example to create first temperature sensor object: lwm2m_engine_create_obj_inst(“3303/0”);

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst”

int lwm2m_engine_set_opaque(char *pathstr, char *data_ptr, uint16_t data_len)¶

Set resource (instance) value (opaque buffer)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] data_ptr: Data buffer
[in] data_len: Length of buffer

int lwm2m_engine_set_string(char *pathstr, char *data_ptr)¶

Set resource (instance) value (string)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] data_ptr: NULL terminated char buffer

int lwm2m_engine_set_u8(char *pathstr, uint8_t value)¶

Set resource (instance) value (u8)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: u8 value

int lwm2m_engine_set_u16(char *pathstr, uint16_t value)¶

Set resource (instance) value (u16)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: u16 value

int lwm2m_engine_set_u32(char *pathstr, uint32_t value)¶

Set resource (instance) value (u32)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: u32 value

int lwm2m_engine_set_u64(char *pathstr, uint64_t value)¶

Set resource (instance) value (u64)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: u64 value

int lwm2m_engine_set_s8(char *pathstr, int8_t value)¶

Set resource (instance) value (s8)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: s8 value

int lwm2m_engine_set_s16(char *pathstr, int16_t value)¶

Set resource (instance) value (s16)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: s16 value

int lwm2m_engine_set_s32(char *pathstr, int32_t value)¶

Set resource (instance) value (s32)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: s32 value

int lwm2m_engine_set_s64(char *pathstr, int64_t value)¶

Set resource (instance) value (s64)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: s64 value

int lwm2m_engine_set_bool(char *pathstr, bool value)¶

Set resource (instance) value (bool)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: bool value

int lwm2m_engine_set_float32(char *pathstr, float32_value_t *value)¶

Set resource (instance) value (32-bit float structure)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: 32-bit float value

int lwm2m_engine_set_float64(char *pathstr, float64_value_t *value)¶

Set resource (instance) value (64-bit float structure)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: 64-bit float value

int lwm2m_engine_set_objlnk(char *pathstr, struct lwm2m_objlnk *value)¶

Set resource (instance) value (ObjLnk)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] value: pointer to the lwm2m_objlnk structure

int lwm2m_engine_get_opaque(char *pathstr, void *buf, uint16_t buflen)¶

Get resource (instance) value (opaque buffer)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] buf: Data buffer to copy data into
[in] buflen: Length of buffer

int lwm2m_engine_get_string(char *pathstr, void *str, uint16_t strlen)¶

Get resource (instance) value (string)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] str: String buffer to copy data into
[in] strlen: Length of buffer

int lwm2m_engine_get_u8(char *pathstr, uint8_t *value)¶

Get resource (instance) value (u8)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] value: u8 buffer to copy data into

int lwm2m_engine_get_u16(char *pathstr, uint16_t *value)¶

Get resource (instance) value (u16)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] value: u16 buffer to copy data into

int lwm2m_engine_get_u32(char *pathstr, uint32_t *value)¶

Get resource (instance) value (u32)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] value: u32 buffer to copy data into

int lwm2m_engine_get_u64(char *pathstr, uint64_t *value)¶

Get resource (instance) value (u64)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] value: u64 buffer to copy data into

int lwm2m_engine_get_s8(char *pathstr, int8_t *value)¶

Get resource (instance) value (s8)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] value: s8 buffer to copy data into

int lwm2m_engine_get_s16(char *pathstr, int16_t *value)¶

Get resource (instance) value (s16)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] value: s16 buffer to copy data into

int lwm2m_engine_get_s32(char *pathstr, int32_t *value)¶

Get resource (instance) value (s32)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] value: s32 buffer to copy data into

int lwm2m_engine_get_s64(char *pathstr, int64_t *value)¶

Get resource (instance) value (s64)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] value: s64 buffer to copy data into

int lwm2m_engine_get_bool(char *pathstr, bool *value)¶

Get resource (instance) value (bool)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] value: bool buffer to copy data into

int lwm2m_engine_get_float32(char *pathstr, float32_value_t *buf)¶

Get resource (instance) value (32-bit float structure)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] buf: 32-bit float buffer to copy data into

int lwm2m_engine_get_float64(char *pathstr, float64_value_t *buf)¶

Get resource (instance) value (64-bit float structure)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] buf: 64-bit float buffer to copy data into

int lwm2m_engine_get_objlnk(char *pathstr, struct lwm2m_objlnk *buf)¶

Get resource (instance) value (ObjLnk)

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] buf: lwm2m_objlnk buffer to copy data into

int lwm2m_engine_register_read_callback(char *pathstr, lwm2m_engine_get_data_cb_t cb)¶

Set resource (instance) read callback.

LwM2M clients can use this to set the callback function for resource reads.

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] cb: Read resource callback

int lwm2m_engine_register_pre_write_callback(char *pathstr, lwm2m_engine_get_data_cb_t cb)¶

Set resource (instance) pre-write callback.

This callback is triggered before setting the value of a resource. It can pass a special data buffer to the engine so that the actual resource value can be calculated later, etc.

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] cb: Pre-write resource callback

int lwm2m_engine_register_post_write_callback(char *pathstr, lwm2m_engine_set_data_cb_t cb)¶

Set resource (instance) post-write callback.

This callback is triggered after setting the value of a resource to the resource data buffer.

It allows an LwM2M client or object to post-process the value of a resource or trigger other related resource calculations.

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] cb: Post-write resource callback

int lwm2m_engine_register_exec_callback(char *pathstr, lwm2m_engine_execute_cb_t cb)¶

Set resource execute event callback.

This event is triggered when the execute method of a resource is enabled.

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res”
[in] cb: Execute resource callback

int lwm2m_engine_register_create_callback(uint16_t obj_id, lwm2m_engine_user_cb_t cb)¶

Set object instance create event callback.

This event is triggered when an object instance is created.

Return

0 for success or negative in case of error.

Parameters

[in] obj_id: LwM2M object id
[in] cb: Create object instance callback

int lwm2m_engine_register_delete_callback(uint16_t obj_id, lwm2m_engine_user_cb_t cb)¶

Set object instance delete event callback.

This event is triggered when an object instance is deleted.

Return

0 for success or negative in case of error.

Parameters

[in] obj_id: LwM2M object id
[in] cb: Delete object instance callback

int lwm2m_engine_set_res_data(char *pathstr, void *data_ptr, uint16_t data_len, uint8_t data_flags)¶

Set data buffer for a resource.

Use this function to set the data buffer and flags for the specified LwM2M resource.

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[in] data_ptr: Data buffer pointer
[in] data_len: Length of buffer
[in] data_flags: Data buffer flags (such as read-only, etc)

int lwm2m_engine_get_res_data(char *pathstr, void **data_ptr, uint16_t *data_len, uint8_t *data_flags)¶

Get data buffer for a resource.

Use this function to get the data buffer information for the specified LwM2M resource.

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res(/res-inst)”
[out] data_ptr: Data buffer pointer
[out] data_len: Length of buffer
[out] data_flags: Data buffer flags (such as read-only, etc)

int lwm2m_engine_create_res_inst(char *pathstr)¶

Create a resource instance.

LwM2M clients use this function to create multi-resource instances: Example to create 0 instance of device available power sources: lwm2m_engine_create_res_inst(“3/0/6/0”);

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res/res-inst”

int lwm2m_engine_delete_res_inst(char *pathstr)¶

Delete a resource instance.

Use this function to remove an existing resource instance

Return

0 for success or negative in case of error.

Parameters

[in] pathstr: LwM2M path string “obj/obj-inst/res/res-inst”

int lwm2m_engine_start(struct lwm2m_ctx *client_ctx)¶

Start the LwM2M engine.

LwM2M clients normally do not need to call this function as it is called by lwm2m_rd_client_start(). However, if the client does not use the RD client implementation, it will need to be called manually.

Return

0 for success or negative in case of error.

Parameters

[in] client_ctx: LwM2M context

void lwm2m_acknowledge(struct lwm2m_ctx *client_ctx)¶

Acknowledge the currently processed request with an empty ACK.

LwM2M engine by default sends piggybacked responses for requests. This function allows to send an empty ACK for a request earlier (from the application callback). The LwM2M engine will then send the actual response as a separate CON message after all callbacks are executed.

Parameters

[in] client_ctx: LwM2M context

void lwm2m_rd_client_start(struct lwm2m_ctx *client_ctx, const char *ep_name, uint32_t flags, lwm2m_ctx_event_cb_t event_cb)¶

Start the LwM2M RD (Registration / Discovery) Client.

The RD client sits just above the LwM2M engine and performs the necessary actions to implement the “Registration interface”. For more information see Section 5.3 “Client Registration Interface” of the LwM2M Technical Specification.

NOTE: lwm2m_engine_start() is called automatically by this function.

Parameters

[in] client_ctx: LwM2M context
[in] ep_name: Registered endpoint name
[in] flags: Flags used to configure current LwM2M session.
[in] event_cb: Client event callback function

void lwm2m_rd_client_stop(struct lwm2m_ctx *client_ctx, lwm2m_ctx_event_cb_t event_cb)¶

Stop the LwM2M RD (De-register) Client.

The RD client sits just above the LwM2M engine and performs the necessary actions to implement the “Registration interface”. For more information see Section 5.3 “Client Registration Interface” of the LwM2M Technical Specification.

Parameters

[in] client_ctx: LwM2M context
[in] event_cb: Client event callback function

struct lwm2m_ctx¶: #include <lwm2m.h>
LwM2M context structure to maintain information for a single LwM2M connection.

struct float32_value¶: #include <lwm2m.h>
32-bit variant of the LwM2M float structure

struct float64_value¶: #include <lwm2m.h>
32-bit variant of the LwM2M float structure

struct lwm2m_objlnk¶: #include <lwm2m.h>
LWM2M ObjLnk resource type structure.

Lightweight M2M (LWM2M)¶

Overview¶

Example LwM2M object and resources: Device¶

Sample usage¶

Using LwM2M library with DTLS¶

API Reference¶

Overview ¶

Example LwM2M object and resources: Device ¶

Sample usage ¶

Using LwM2M library with DTLS ¶

API Reference ¶