How to use the Asset Data API to manage a smart device.

Overview

A smart device can control many things - (e.g., temperature sensors, or electronic switches) . Data can be collected from the devices and categorized into variables, settings, and commands. The AirVantage data API lets you work with the variables, settings and commands from a smart device and sync them with the AirVantage Cloud Service.

For more detail regarding the AssetData API, please refer to AirVantage Data API.

Variables, Settings and Commands

To control a smart device, call le_avdata_CreateResource API to create a resource, which is referred to with a unique path. "Set" and "Get" functions are included to write and read values on the client (i.e. app) side, and the AirVantage server can read and write values to your app as well.

For example, the device can read the thermostat hardware for the current temperature, and call the "le_avdata_SetFloat" API to store the temperature value to the device, which the AirVantage server can query for the temperature value.

static double Thermostat_GetTemp
(
    void
)
{
    // Reads from the thermostat hardware and returns the current temperature value
}
 
 le_avdata_CreateResource("/room1/thermostat/temperature", LE_AVDATA_ACCESS_VARIABLE);
 
 le_avdata_SetFloat("/room1/thermostat/temperature", Thermostat_GetTemp());

With each resource, a function can be optionally registered (with the le_avdata_AddResourceEventHandler API) to be called whenever the AirVantage server reads from or writes to the function. This is useful to perform tasks associated with reading/writing sensor data.

For example, when the AirVantage server writes to a temperature setting, a function is called to check the current temperature, and turn on the air conditioning if necessary.

static void AccessTempSettingHandler
(
    const char* path,
    le_avdata_AccessType_t accessType,
    le_avdata_ArgumentListRef_t argumentList,
    void* contextPtr
)
{
    // Obtain the current temperature reading.
    double currentTemp = Thermostat_GetTemp();
 
    // Obtain the temperature setting from the AirVantage server.
    double tempSetting = 0;
    le_avdata_GetFloat(path, &tempSetting);
 
    // Turn on the air conditioning if the current temperature differs from the desired temperature by more than 5 degrees.
    if (fabs(currentTemp - tempSetting) > 5)
    {
        // Turn on the A/C
    }
}
 
le_avdata_CreateResource("/room1/thermostat/temperatureControl", LE_AVDATA_ACCESS_SETTING);
 
le_avdata_AddResourceEventHandler("/room1/thermostat/temperatureControl", AccessTempSettingHandler, NULL);

Commands do not store values, and must be registered with functions.

static le_result_t FancyFanControl
(
    bool isOn,                 // false is off, true is on
    double fanSpeed            // from 0 to 1, from weakest to the strongest
)
{
    // This demonstrates the ability to return command execution result to the AirVantage server.
    if (fanSpeed > 1)
    {
        return LE_FAULT;
    }
 
    // Actuate the fan with the supplied settings.
 
    return LE_OK;
}
 
static void ExecFanCtrlCmd
(
    const char* path,
    le_avdata_AccessType_t accessType,
    le_avdata_ArgumentListRef_t argumentList,
    void* contextPtr
)
{
    bool isOn = false;
    double fanSpeed = 0;
 
    // Obtain the arguments that the AirVantage server sends to the device.
    // Note that "isOn" and "fanSpeed" are argument names to extract the arguments with.
    le_avdata_GetBoolArg(argumentList, "isOn", &isOn);
    le_avdata_GetFloatArg(argumentList, "fanSpeed", &fanSpeed);
 
    // Perform the actual fan control with the arguments
    le_result_t cmdExeResult = FancyFanControl(isOn, fanSpeed);
 
    // Reply the AirVantage server with the command execution result.
    le_avdata_ReplyExecResult(argumentList, cmdExeResult);
}
 
le_avdata_CreateResource("/room1/fanControl", LE_AVDATA_ACCESS_COMMAND);
 
le_avdata_AddResourceEventHandler("/room1/fanControl", ExecFanCtrlCmd, NULL);

Asset Data Models

AirVantage 2.0 removed the need to create Asset Data Models in the .cdef. You now have the option to use the AirVantage Web Services API to control your data, and you do not need to create an Asset Data Model.

If you wish to use the AirVantage Web Portal GUI to control the asset data then you must manually create the model and upload it to the AirVantage Server before being able to control your data.

AirVantage Application Format Reference will guide you through creating an Application Model to upload to AirVantage.

Example Application Model

<?xml version="1.0" encoding="UTF-8"?>
<app:application xmlns:app="http://www.sierrawireless.com/airvantage/application/1.0" name="assetData" type="assetData-legato-application" revision="1.00">
    <application-manager use="LWM2M_SW"/>
    <capabilities>
        <data>
            <encoding type="LWM2M">
                <asset default-label="home1" id="home1">
                    <node path="room1" default-label="room1">
 
                        <node path="SmartCam" default-label="SmartCam">
                            <variable path="numPeople" type="int" default-label="numPeople" />
                            <variable path="numDogs" type="int" default-label="numDogs" />
                        </node>
 
                        <variable path="roomName" type="string" default-label="roomName" />
                        <variable path="isVacant" type="boolean" default-label="isVacant" />
 
                        <node path="thermostat" default-label="thermostat">
                            <variable path="tempReading" type="double" default-label="tempReading"  />
                            <setting path="tempSetting" type="double" default-label="tempSetting"/>
                            <setting path="strengthSetting" type="int" default-label="strengthSetting"/>
                            <setting path="powerSetting" type="boolean" default-label="powerSetting"/>
                            <setting path="lcdtextSetting" type="string" default-label="lcdtextSetting"/>
                        </node>
 
                        <node path="fan" default-label="fan">
                            <command path="fanControl" default-label="fanControl">
                                <parameter id="customText" default-label="customText" type="string" />
                                <parameter id="isOn" default-label="isOn" type="boolean" />
                                <parameter id="fanMovement" default-label="fanMovement" type="int" />
                                <parameter id="fanSpeed" default-label="fanSpeed" type="double" />
                            </command>
                        </node>
 
                    </node>
                </asset>
            </encoding>
        </data>
    </capabilities>
</app:application>

Note

For further details on creating an Asset Data model see the sample application located in the {LEGATO_ROOT}/apps/sample/assetData

TimeSeries

A series of data points with time stamps can be collected and sent to the AirVantage server with the Time Series API. This is useful for collecting historical data and analyzing trend.

For example, the room temperature every hour for the past 24 hours.

static void PushCallbackHandler
(
    le_avdata_PushStatus_t status,
    void* contextPtr
)
{
    if (status == LE_AVDATA_PUSH_SUCCESS)
    {
        // data pushed successfully
    }
}
 
static void SendData()
{
    struct timeval tv;
    uint64_t utcMilliSec;
    le_result_t result;
 
    le_avdata_RecordRef_t recRef = le_avdata_CreateRecord();
 
    gettimeofday(&tv, NULL);
    utcMilliSec = (uint64_t)(tv.tv_sec) * 1000 + (uint64_t)(tv.tv_usec) / 1000; // get current time
    result = le_avdata_RecordFloat(recRef, "speed", 0.08, utcMilliSec);
 
    if (result != LE_OK)
    {
         le_avdata_PushRecord(recRef, PushCallbackHandler, NULL);
    }
 
    le_avdata_DeleteRecord(recRef);
}
 
le_timer_Ref_t timer = le_timer_Create("CollectRoomTemperatureData");
le_clk_Time_t interval = {3600, 0}; // every hour
le_timer_SetInterval(timer, interval);
le_timer_SetRepeat(timer, 0); // repeat indefinitely
le_timer_SetHandler(timer, ValueUpdate);
le_timer_Start(timer);