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SVGHMI instances configuration

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==============================

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.. list-table::

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    * - Multiple SVGHMI instances can be configured simultaneously in the same Beremiz  :doc:`../programming/configuration`, exposing different HMIs.

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        .. image:: svghmi_multi.png

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      - .. figure:: svghmi_configuration.png

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        SVGHMI configuration panel

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Ports, interfaces, path and MaxConnections

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    Each SVGHMI instance must bind to different interface-port-path triplet. In case of conflict, a build error is issued.

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    By default, interface is set to ``localhost``, port to ``8008`` and path is set to :doc:`../programming/configuration` Node's name: ``{name}``.

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    As an example, in case SVGHMI instance is first node in :doc:`../programming/configuration`, default URL to reach HMI is ``http://localhost:8008/svghmi_0``

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    Up to ``MaxConnections`` clients (i.e. web browser) can connect to the same SVGHMI instance simultaneously.

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    This number has an influence on memory footprint of generated code.

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    In case of repeated connection loss with long TCP `TTL <https://en.wikipedia.org/wiki/Time_to_live>`_, small ``MaxConnections`` number can lead to connection refusal.

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About Security

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^^^^^^^^^^^^^^

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 ..

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    TODO :

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Watchdog

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--------

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    Purpose of SVGHMI watchdog is to detect if HMI is still functioning and connected to PLC.

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    ``/HEARTBEAT`` variable is periodically updated by PLC and HMI to detect failure.

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    When SVHGMI server doesn't receive HMI heartbeat in due time, watchdog is triggered, and ``OnWatchdog`` command is executed. 

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    For example, ``OnWatchdog`` can be used to restart a new web browser in case it did crash.

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    Only one single client can use watchdog at a time, and ``Watchdog`` configuration setting can be active on only one SVGHMI instance at a time.

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    ``WatchdogInitial`` and ``WatchdogInterval`` define how long watchdog will accept to wait before receiving first heartbeat,

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    and then how long it will wait in between heartbeats once first heartbeat has been received.

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Starting and stopping browser

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-----------------------------

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    ``OnStart`` and ``OnStop`` configuration settings are commands meant control web browser execution when PLC is started or stopped.

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    PID of commands are monitored, and the end of web browser process is awaited after command. 

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    If web browser process isn't finished 3s after calling ``OnStop`` command, warning is logged.