Get started with C (ESP32)¶

Follow this guide to get started with the Astarte device SDK for ESP32 devices.

Generating a device ID¶

A device ID will be required to uniquely identify a device in an Astarte instance. Some of the Astarte device SDKs provide utilities to generate a deterministic or random device identifier, in some cases based on hardware information.

This step is only useful when registering a device using a JWT token and the provided Astarte device SDKs registration APIs. Registration of a device can also be performed outside the device in the Astarte instance. In such cases the device ID should be obtained via astartectl, or the Astarte dashboard. The device ID should then be loaded manually on the device.

Generating a device ID from device MAC address and other hardware identification bits:

astarte_err_t astarte_hwid_get_id(&hw_id);

Registering a device¶

In order for a device to connect to Astarte a registration procedure is required. This registration will produce a device specific credential secret that will be used when connecting to Astarte. Some of the Astarte device SDKs provide utilities to perform a device registration directly on the device. Those APIs will require a registration JWT to be uploaded to the device. Such JWT should be discarded following the registration procedure.

This step is only useful when registering the device through the APIs using the JWT token. Registration of a device can also be performed outside the device in the Astarte instance using tools such as astartectl, the Astarte dashboard, or the dedicated Astarte API for device registration. The generated credential secret should then be loaded manually on the device.

astarte_pairing_config cfg =
{
.base_url = &base_astarte_url;
.jwt = &jwt_token;
.realm = &realm;
.hw_id = &device_id;
.credentials_secret = &credentials_secret;
};

astarte_err_t err = astarte_pairing_register_device(&astarte_pairing_config);

Instantiating and connecting a new device¶

Now that we obtained both a device ID and a credential secret we can create a new device instance. Some of the SDKs will connect instantly as soon as the device is instantiated while others will require a call to a connect function. Furthermore, depending on the SDK the introspection of the device might be defined while instantiating the device or between instantiation and connection.

// Instantiating a device
astarte_device_config_t cfg = {
    .data_event_callback = astarte_data_events_handler,
    .unset_event_callback = astarte_unset_events_handler,
    .connection_event_callback = astarte_connection_events_handler,
    .disconnection_event_callback = astarte_disconnection_events_handler,
    .credentials_secret = cred_sec,
    .hwid = hwid,
    .realm = realm,
};
astarte_device_handle_t device = astarte_device_init(&cfg);
if (!device) {
    ESP_LOGE(TAG, "Failed to init astarte device");
    return;
}
// Adding an interface
astarte_device_add_interface(device, &device_example_interface);
// Starting a device
if (astarte_device_start(device) != ASTARTE_OK) {
    ESP_LOGE(TAG, "Failed to start astarte device");
    return;
}

Streaming data¶

All Astarte Device SDKs include primitives for sending data to a remote Astarte instance. Streaming of data could be performed for device owned interfaces of individual or object aggregation type.

Streaming individual data¶

In Astarte interfaces with individual aggregation, each mapping is treated as an independent value and is managed individually.

The snippet bellow shows how to send a value that will be inserted into the "/test0/value" datastream which is defined by "/%{sensor_id}/value" parametric endpoint, that is part of "org.astarte-platform.genericsensors.Values" datastream interface.

struct timeval tv;
gettimeofday(&tv, NULL);
uint64_t ts = tv->tv_sec * 1000 + tv->tv_usec / 1000;

astarte_err_t err = astarte_device_stream_double_with_timestamp(device, "org.astarte-platform.genericsensors.Values", "/test0/value", 0.3, ts, 0);

Streaming aggregated data¶

In Astarte interfaces with object aggregation, Astarte expects the owner to send all of the interface’s mappings at the same time, packed in a single message.

The following snippet shows how to send a value for an object aggregated interface. In this examples, lat and long will be sent together and will be inserted into the "/coords" datastream which is defined by the "/coords" endpoint, that is part of "com.example.GPS" datastream interface.

astarte_bson_serializer_init(&bs);
astarte_bson_serializer_append_double(&bs, "lat", 45.409627);
astarte_bson_serializer_append_double(&bs, "long", 11.8765254);
astarte_bson_serializer_append_end_of_document(&bs);
int size;
const void *coord = astarte_bson_serializer_get_document(&bs, &size);

struct timeval tv;
gettimeofday(&tv, NULL);
uint64_t ts = tv->tv_sec * 1000 + tv->tv_usec / 1000;

astarte_device_stream_aggregate_with_timestamp(device, "com.example.GPS", "/coords", coords, ts, 0);

Setting and unsetting properties¶

Interfaces of property type represent a persistent, stateful, synchronized state with no concept of history or timestamping. From a programming point of view, setting and unsetting properties of device-owned interface is rather similar to sending messages on datastream interfaces.

The following snippet shows how to set a value that will be inserted into the "/sensor0/name" property which is defined by "/%{sensor_id}/name" parametric endpoint, that is part of "org.astarte-platform.genericsensors.AvailableSensors" device-owned properties interface.

It should be noted how a property should be marked as unsettable in its interface definition to be able to use the unsetting method on it.

Set property:

astarte_device_set_string_property(device, "org.astarte-platform.genericsensors.AvailableSensors", "/sensor0/name", "foobar");

Unset property:

astarte_device_unset_path(device, "org.astarte-platform.genericsensors.AvailableSensors", "/sensor0/name");