Synchronization Sequence

This section describes the sequence of calls to different DeviceDriver methods by the server core during synchronization of the device with the server.

1. If device is suspended, synchronization is skipped.

2. If device dependency expression evaluates to false, synchronization is skipped and device switches to Offline connection status.

3. Driver's should shouldSynchronize() method is called. If it returns false (e.g. if device communication settings were not yet defined), synchronization is skipped.

4. If extended status is enabled, device's synchronization status switches to Connecting.

5. If isUsesConnections() method of the driver returns true:

  • 1. If isConnected() returns false or system core requests reconnection to the hardware (e.g. because previous sync has failed and Interrupt Synchronization On Error is enabled), the system calls disconnect() (only if isConnected() is true) and then connect().
  • 2.If connect() doesn't throw an exception, device switches to Online connection status.

6. Certain synchronization tasks called "connect-only" tasks may end at this point.

7. If extended status is enabled, device's synchronization status switches to Reading Metadata.

8. startSynchronization() is called.

9. If synchronization parameters request metadata reading (i.e. "full" synchronization is performed):

  • 1. If driver supports groups (i.e. isUsesGroups() returns true) and groups has not yet been read from device (or driver was reset), readGroupDefinitions() method is called.
  • 2. readVariableDefinitions() is called, new and changed definitions are added to the device context and cached in database. If driver supports groups, readVariableDefinitions(List<GroupDefinition>) method is called instead.
  • 3. If synchronization settings of some newly added variable definitions have custom synchronization period, per-setting synchronization tasks are scheduled.
  • 4. readFunctionDefinitions() is called, new and changed definitions are added to the device context and cached. If driver supports groups, readFunctionDefinitions(List<GroupDefinition>) method is called instead.
  • 5. Corresponding Call Function action is added to device context for every new function definition.
  • 6. readEventDefinitions() is called, new and changed definitions are added to the device context and cached. If driver supports groups, readEventDefinitions(List<GroupDefinition>) method is called instead.
  • 7. If any of the above read methods throw a DisconnectionException, the error is logged, device switches to Offline connection status, driver's disconnect() method is called, and synchronization is terminated.

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