3 Data Sources

A data source is a control process that provides signals and parameters via the network. In order to connect to it, it needs to offer a protocol that is supported by the PdCom library (for example the MSR protocol). A typical data source is a real-time application built with PdServ, for example a Simulink model generated with EtherLab or a C/C++ application using the PdServ library.

Tip

If PdServ is installed, the command pdserv-example-st starts a small example process that can be used to try out all features described in this manual. See the example chapter for a complete walk-through.

3.1 Adding a data source

Select Data Sources → Add data source... or right-click into the data source tree and select Add datasource.... Enter the URL of the process:

URL scheme	Default port	Description
`msr://`	2345	Unencrypted connection
`msrs://`	4523	Connection encrypted via TLS

For example, msr://localhost connects to a process on the local machine. Process variables are referenced by URLs of the form msr://host:port/path/to/variable.

For encrypted connections, the server certificate can either be ignored or verified against a custom CA certificate. These settings are stored per host and port.

3.2 Observing the connection

The context menu of a data source offers the following actions: Connect, Disconnect, Login, Logout, Remove, Replace..., Show messages... and Configure messages....

Data Sources → Connect to data sources connects all data sources referenced in the current layout.

3.3 Authentication

If the process requires authentication, select Login from the context menu of the data source and enter user name and password.

3.4 Browsing a data source

After connecting, the Data Sources dock shows a tree of all signals and parameters of the process.

Signals are values calculated by the process. They can only be read.
Parameters can be read and written.

The icon in front of a variable shows its kind:

Icon	Meaning
	Signal, currently not subscribed
	Signal, subscribed periodically
	Signal, subscribed event-based
	Parameter

Each variable has a sample time. The value 0 means that the variable is not sampled periodically, but transmitted event-based, i.e. only when its value changes. Parameters are always event-based.

Important

Within one connection to a process, a signal can be transmitted either event-based (period 0) or periodically (period > 0). Therefore use either event-based or periodic transmission consistently for a signal.

A filter expression above the tree limits the displayed variables.

The context menu of a variable offers:

Copy variable URL: Copies the URL to the clipboard.
Select subscribers: Selects all widgets that are connected to the variable.
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