Device Variables (Settings)

Device variables (also called device setting variables or device settings) are variables of a device context that are mapped to the settings of the hardware device by the corresponding device driver.

It's important to discern device setting variables (such as measured temperature) from variables of a device context that match configuration properties of the device account (such as device IP address and port number). Device setting variables are read/written from/to the actual hardware device or data source, while account property variables just define server-side device communication parameters.

Device setting variables have some peculiarities:

  • During the initial device synchronization, the server creates a device snapshot, i.e. server-side settings cache that contains the most recent values of device settings received from the hardware device or data source.

  • Device variables that are not retrieved because of an error during the initial synchronization will not appear in the list of available variables in the Iotellect device context. However, synchronization errors will generate informative device events that help diagnose the situation once some device variables are missing.

  • Each device setting variable may have a custom synchronization (polling) period, history storage duration, and other per-setting synchronization options.

  • Each device setting variable has an associated synchronization status. Those synchronization statuses define aggregated synchronization status of the whole device account.

  • Once a device setting variable is read by any system module or an external application, its value is retrieved from the server-side device settings cache and returned. No device I/O is performed unless the setting uses direct synchronization mode.

  • Once a device setting variable is written by any system module or an external application, the new value is written to the server-side device settings cache and a partial synchronization is requested. No synchronous device I/O is performed unless the setting uses direct synchronization mode.

  • In addition to configuring the database storage period for "raw" historical values of device setting variables, it's possible to create statistical channels for aggregating them in a round-robin database to ensure compact storage and fast access.

Examples of device settings:

  • "Temperature" read-only setting of thermometer supporting Modbus TCP protocol.

  • Tabular read-only setting of an SNMP-capable network host that represents the table of device's network interfaces.

  • Writable "Orientation" setting of an access control terminal. The setting could be set to "Desktop" or "Wall mount".

Was this page helpful?