Run variables

Run variables

Run variables are Tcl variables that are registered with Readout to be periodically logged to the event stream in run variable documentation buffers. Run variables can be changed at any time, either by a script or by the C/C++ code. They are intended to document the change in value of experimental paramters that might drift in the course of a run. The CRunVariable class that implements run variables is derived from CTCLVariable.

To create a Run variable, you can either:

• use the runvar command as described in The runvar command.
• Create them programmatically in your C/C++ code.

To programmatically create a runvar you need to:

• Provide a mechanism to access the variable you have created.
• Create an instance of a the variable.

The example below shows how to create a run variable. This code fragment should be put in the SetupRunVariables function.

            ...
            CRunVariableCommand* pRunvarCommand = 
                  rCore.getRunVariables();
            CRunVariable* pTemp = 
                  pRunvarCommand.Create(string("temperature"),
                                                     getTemperature());
            if(!pTemp) {
               cerr << "Attempted to double create runvar "temperature"
                     << endl;
            }
            ...
         

In the example above, getTemperature() is assumed to be a function that returns a string value for the current temperature being monitored.

Once created, you can choose any of the mechanisms described in Ordinary Tcl variables to provide access to it.

If you want to update the variable periodically, you have several choices:

• Provide a Tcl command that can determine the new vairable value and update the variable in a rescheduled after Tcl command at script level.
• If the variable comes from some external source, enable the Tcl server and have a client periodically set the variable across its connection to readout.
• Schedule a periodic action to update the data when the run is active; See: Arranging for periodic actions.

Run variables