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iot-suite-connecting-code.md

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Specify the behavior of the IoT device

The IoT Hub serializer client library uses a model to specify the format of the messages the device exchanges with IoT Hub.

  1. Add the following variable declarations after the #include statements. Replace the placeholder values [Device Id] and [Device Key] with values you noted for your device in the remote monitoring solution dashboard. Use the IoT Hub Hostname from the solution dashboard to replace [IoTHub Name]. For example, if your IoT Hub Hostname is contoso.azure-devices.net, replace [IoTHub Name] with contoso:

    static const char* deviceId = "[Device Id]";
static const char* connectionString = "HostName=[IoTHub Name].azure-devices.net;DeviceId=[Device Id];SharedAccessKey=[Device Key]";

  2. Add the following code to define the model that enables the device to communicate with IoT Hub. This model specifies that the device:

    • Can send temperature, external temperature, humidity, and a device id as telemetry.
    • Can send metadata about the device to IoT Hub. The device sends basic metadata in a DeviceInfo object at startup.
    • Can send reported properties, to the device twin in IoT Hub. These reported properties are grouped into configuration, device, and system properties.
    • Can receive and act on desired properties set in the device twin in IoT Hub.
    • Can respond to the Reboot and InitiateFirmwareUpdate direct methods invoked through the solution portal. The device sends information about the direct methods it supports using reported properties.
    // Define the Model
BEGIN_NAMESPACE(Contoso);

/* Reported properties */
DECLARE_STRUCT(SystemProperties,
  ascii_char_ptr, Manufacturer,
  ascii_char_ptr, FirmwareVersion,
  ascii_char_ptr, InstalledRAM,
  ascii_char_ptr, ModelNumber,
  ascii_char_ptr, Platform,
  ascii_char_ptr, Processor,
  ascii_char_ptr, SerialNumber
);

DECLARE_STRUCT(LocationProperties,
  double, Latitude,
  double, Longitude
);

DECLARE_STRUCT(ReportedDeviceProperties,
  ascii_char_ptr, DeviceState,
  LocationProperties, Location
);

DECLARE_MODEL(ConfigProperties,
  WITH_REPORTED_PROPERTY(double, TemperatureMeanValue),
  WITH_REPORTED_PROPERTY(uint8_t, TelemetryInterval)
);

/* Part of DeviceInfo */
DECLARE_STRUCT(DeviceProperties,
  ascii_char_ptr, DeviceID,
  _Bool, HubEnabledState
);

DECLARE_DEVICETWIN_MODEL(Thermostat,
  /* Telemetry (temperature, external temperature and humidity) */
  WITH_DATA(double, Temperature),
  WITH_DATA(double, ExternalTemperature),
  WITH_DATA(double, Humidity),
  WITH_DATA(ascii_char_ptr, DeviceId),

  /* DeviceInfo */
  WITH_DATA(ascii_char_ptr, ObjectType),
  WITH_DATA(_Bool, IsSimulatedDevice),
  WITH_DATA(ascii_char_ptr, Version),
  WITH_DATA(DeviceProperties, DeviceProperties),

  /* Device twin properties */
  WITH_REPORTED_PROPERTY(ReportedDeviceProperties, Device),
  WITH_REPORTED_PROPERTY(ConfigProperties, Config),
  WITH_REPORTED_PROPERTY(SystemProperties, System),

  WITH_DESIRED_PROPERTY(double, TemperatureMeanValue, onDesiredTemperatureMeanValue),
  WITH_DESIRED_PROPERTY(uint8_t, TelemetryInterval, onDesiredTelemetryInterval),

  /* Direct methods implemented by the device */
  WITH_METHOD(Reboot),
  WITH_METHOD(InitiateFirmwareUpdate, ascii_char_ptr, FwPackageURI),

  /* Register direct methods with solution portal */
  WITH_REPORTED_PROPERTY(ascii_char_ptr_no_quotes, SupportedMethods)
);

END_NAMESPACE(Contoso);

Implement the behavior of the device

Now add code that implements the behavior defined in the model.

  1. Add the following functions that handle the desired properties set in the solution dashboard. These desired properties are defined in the model:

    void onDesiredTemperatureMeanValue(void* argument)
{
  /* By convention 'argument' is of the type of the MODEL */
  Thermostat* thermostat = argument;
  printf("Received a new desired_TemperatureMeanValue = %f\r\n", thermostat->TemperatureMeanValue);

}

void onDesiredTelemetryInterval(void* argument)
{
  /* By convention 'argument' is of the type of the MODEL */
  Thermostat* thermostat = argument;
  printf("Received a new desired_TelemetryInterval = %d\r\n", thermostat->TelemetryInterval);
}

  2. Add the following functions that handle the direct methods invoked through the IoT hub. These direct methods are defined in the model:

    /* Handlers for direct methods */
METHODRETURN_HANDLE Reboot(Thermostat* thermostat)
{
  (void)(thermostat);

  METHODRETURN_HANDLE result = MethodReturn_Create(201, "\"Rebooting\"");
  printf("Received reboot request\r\n");
  return result;
}

METHODRETURN_HANDLE InitiateFirmwareUpdate(Thermostat* thermostat, ascii_char_ptr FwPackageURI)
{
  (void)(thermostat);

  METHODRETURN_HANDLE result = MethodReturn_Create(201, "\"Initiating Firmware Update\"");
  printf("Recieved firmware update request. Use package at: %s\r\n", FwPackageURI);
  return result;
}

  3. Add the following function that sends a message to the preconfigured solution:

    /* Send data to IoT Hub */
static void sendMessage(IOTHUB_CLIENT_HANDLE iotHubClientHandle, const unsigned char* buffer, size_t size)
{
  IOTHUB_MESSAGE_HANDLE messageHandle = IoTHubMessage_CreateFromByteArray(buffer, size);
  if (messageHandle == NULL)
  {
    printf("unable to create a new IoTHubMessage\r\n");
  }
  else
  {
    if (IoTHubClient_SendEventAsync(iotHubClientHandle, messageHandle, NULL, NULL) != IOTHUB_CLIENT_OK)
    {
      printf("failed to hand over the message to IoTHubClient");
    }
    else
    {
      printf("IoTHubClient accepted the message for delivery\r\n");
    }

    IoTHubMessage_Destroy(messageHandle);
  }
  free((void*)buffer);
}

  4. Add the following callback handler that runs when the device has sent new reported property values to the preconfigured solution:

    /* Callback after sending reported properties */
void deviceTwinCallback(int status_code, void* userContextCallback)
{
  (void)(userContextCallback);
  printf("IoTHub: reported properties delivered with status_code = %u\n", status_code);
}

  5. Add the following function to connect your device to the preconfigured solution in the cloud, and exchange data. This function performs the following steps:

    • Initializes the platform.

    • Registers the Contoso namespace with the serialization library.

    • Initializes the client with the device connection string.

    • Create an instance of the Thermostat model.

    • Creates and sends reported property values.

    • Sends a DeviceInfo object.

    • Creates a loop to send telemetry every second.

    • Deinitializes all resources.

      void remote_monitoring_run(void)
{
  if (platform_init() != 0)
  {
    printf("Failed to initialize the platform.\n");
  }
  else
  {
    if (SERIALIZER_REGISTER_NAMESPACE(Contoso) == NULL)
    {
      printf("Unable to SERIALIZER_REGISTER_NAMESPACE\n");
    }
    else
    {
      IOTHUB_CLIENT_HANDLE iotHubClientHandle = IoTHubClient_CreateFromConnectionString(connectionString, MQTT_Protocol);
      if (iotHubClientHandle == NULL)
      {
        printf("Failure in IoTHubClient_CreateFromConnectionString\n");
      }
      else
      {
#ifdef MBED_BUILD_TIMESTAMP
        // For mbed add the certificate information
        if (IoTHubClient_SetOption(iotHubClientHandle, "TrustedCerts", certificates) != IOTHUB_CLIENT_OK)
        {
            printf("Failed to set option \"TrustedCerts\"\n");
        }
#endif // MBED_BUILD_TIMESTAMP
        Thermostat* thermostat = IoTHubDeviceTwin_CreateThermostat(iotHubClientHandle);
        if (thermostat == NULL)
        {
          printf("Failure in IoTHubDeviceTwin_CreateThermostat\n");
        }
        else
        {
          /* Set values for reported properties */
          thermostat->Config.TemperatureMeanValue = 55.5;
          thermostat->Config.TelemetryInterval = 3;
          thermostat->Device.DeviceState = "normal";
          thermostat->Device.Location.Latitude = 47.642877;
          thermostat->Device.Location.Longitude = -122.125497;
          thermostat->System.Manufacturer = "Contoso Inc.";
          thermostat->System.FirmwareVersion = "2.22";
          thermostat->System.InstalledRAM = "8 MB";
          thermostat->System.ModelNumber = "DB-14";
          thermostat->System.Platform = "Plat 9.75";
          thermostat->System.Processor = "i3-7";
          thermostat->System.SerialNumber = "SER21";
          /* Specify the signatures of the supported direct methods */
          thermostat->SupportedMethods = "{\"Reboot\": \"Reboot the device\", \"InitiateFirmwareUpdate--FwPackageURI-string\": \"Updates device Firmware. Use parameter FwPackageURI to specifiy the URI of the firmware file\"}";

          /* Send reported properties to IoT Hub */
          if (IoTHubDeviceTwin_SendReportedStateThermostat(thermostat, deviceTwinCallback, NULL) != IOTHUB_CLIENT_OK)
          {
            printf("Failed sending serialized reported state\n");
          }
          else
          {
            printf("Send DeviceInfo object to IoT Hub at startup\n");

            thermostat->ObjectType = "DeviceInfo";
            thermostat->IsSimulatedDevice = 0;
            thermostat->Version = "1.0";
            thermostat->DeviceProperties.HubEnabledState = 1;
            thermostat->DeviceProperties.DeviceID = (char*)deviceId;

            unsigned char* buffer;
            size_t bufferSize;

            if (SERIALIZE(&buffer, &bufferSize, thermostat->ObjectType, thermostat->Version, thermostat->IsSimulatedDevice, thermostat->DeviceProperties) != CODEFIRST_OK)
            {
              (void)printf("Failed serializing DeviceInfo\n");
            }
            else
            {
              sendMessage(iotHubClientHandle, buffer, bufferSize);
            }

            /* Send telemetry */
            thermostat->Temperature = 50;
            thermostat->ExternalTemperature = 55;
            thermostat->Humidity = 50;
            thermostat->DeviceId = (char*)deviceId;

            while (1)
            {
              unsigned char*buffer;
              size_t bufferSize;

              (void)printf("Sending sensor value Temperature = %f, Humidity = %f\n", thermostat->Temperature, thermostat->Humidity);

              if (SERIALIZE(&buffer, &bufferSize, thermostat->DeviceId, thermostat->Temperature, thermostat->Humidity, thermostat->ExternalTemperature) != CODEFIRST_OK)
              {
                (void)printf("Failed sending sensor value\r\n");
              }
              else
              {
                sendMessage(iotHubClientHandle, buffer, bufferSize);
              }

              ThreadAPI_Sleep(1000);
            }

            IoTHubDeviceTwin_DestroyThermostat(thermostat);
          }
        }
        IoTHubClient_Destroy(iotHubClientHandle);
      }
      serializer_deinit();
    }
  }
  platform_deinit();
}

    
For reference, here is a sample **Telemetry** message sent to the preconfigured solution:

    {"DeviceId":"mydevice01", "Temperature":50, "Humidity":50, "ExternalTemperature":55}