edouard@3936: SVGHMI instances configuration
edouard@3936: ==============================
edouard@3925: 
edouard@3936: .. list-table::
edouard@3936: 
edouard@3936:     * - Multiple SVGHMI instances can be configured simultaneously in the same Beremiz  :doc:`../programming/configuration`, exposing different HMIs.
edouard@3936: 
edouard@3936:         .. image:: svghmi_multi.png
edouard@3936: 
edouard@3936:       - .. figure:: svghmi_configuration.png
edouard@3936: 
edouard@3936:         SVGHMI configuration panel
edouard@3936: 
edouard@3936: Ports, interfaces, path and MaxConnections
edouard@3936: ------------------------------------------
edouard@3936: 
edouard@3936:     Each SVGHMI instance must bind to different interface-port-path triplet. In case of conflict, a build error is issued.
edouard@3936: 
edouard@3936:     By default, interface is set to ``localhost``, port to ``8008`` and path is set to :doc:`../programming/configuration` Node's name: ``{name}``.
edouard@3936:     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``
edouard@3936: 
edouard@3936:     Up to ``MaxConnections`` clients (i.e. web browser) can connect to the same SVGHMI instance simultaneously.
edouard@3936:     This number has an influence on memory footprint of generated code.
edouard@3936:     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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edouard@3936: 
edouard@3936: 
edouard@3936: About Security
edouard@3936: ^^^^^^^^^^^^^^
edouard@3936: 
edouard@3936:  ..
edouard@3936:     TODO :
edouard@3936: 
edouard@3925: 
edouard@3925: Watchdog
edouard@3925: --------
edouard@3925: 
edouard@3936:     Purpose of SVGHMI watchdog is to detect if HMI is still functioning and connected to PLC.
edouard@3936:     ``/HEARTBEAT`` variable is periodically updated by PLC and HMI to detect failure.
edouard@3936:     
edouard@3936:     When SVHGMI server doesn't receive HMI heartbeat in due time, watchdog is triggered, and ``OnWatchdog`` command is executed. 
edouard@3936:     For example, ``OnWatchdog`` can be used to restart a new web browser in case it did crash.
edouard@3925: 
edouard@3936:     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.
edouard@3936: 
edouard@3936:     ``WatchdogInitial`` and ``WatchdogInterval`` define how long watchdog will accept to wait before receiving first heartbeat,
edouard@3936:     and then how long it will wait in between heartbeats once first heartbeat has been received.
edouard@3936: 
edouard@3936: 
edouard@3936: Starting and stopping browser
edouard@3936: -----------------------------
edouard@3936: 
edouard@3936:     ``OnStart`` and ``OnStop`` configuration settings are commands meant control web browser execution when PLC is started or stopped.
edouard@3936:     PID of commands are monitored, and the end of web browser process is awaited after command. 
edouard@3936:     If web browser process isn't finished 3s after calling ``OnStop`` command, warning is logged.