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User Event Signal Plot

Overview

The User Event Signal Plot view displays plots of data values from LTTng UST tracepoints configured as User Events. Each plotted curve is denoted a signal, which is a group of user events according to the definition of the signal (see Signal Setup, below).

Plotting of user event signals is useful for, e.g., analysing control system inputs and outputs, but you can use it to visualize any data you like, also discrete values like states. Like other Tracealyzer views, this is connected to the main trace view, which allows for correlating the signal values with the task scheduling and other recorded events. For instance, if you spot an anomaly in a monitored output signal of a control loop, you can click on the data point to show the specific user event in the trace view. This allows you to analyze what was going on at this time - perhaps the scheduling caused an extra delay of the control loop task which affected the signal.

You can combine this view with other horizontal views by choosing "Views" -> "Add" -> (graph type). Like in other Tracealyzer plot views, you can adjust the rendering of the plot using "Views" -> "User Event Signal Plot".

When the User Event Signal Plot is opened, the Signal Setup dialog (described below) is also opened. The Signal Setup can also be opened from the User Event Signal Plot window menu, under "Customize" -> "Signal Setup".

Read more about user events in the LTTng UST section.

Signal Setup

When opening User Event Signal Plot, another window is also opened - Signal Setup. This dialog allows you to create signals for plotting of user events data. A signal is essentially a filter that is applied on all user event strings to extract the values to plot, in the form of a regular expression and some related settings. Two signals are predefined, intended for use with the included demo trace, but you can delete or edit them as you please. There are also general templates available that are easy to import and adapt to your needs. Note that all changes made are stored on disk automatically.

In the left part of the Signal Setup, your signals are shown in a list view and below there are a set of buttons to manage your signals:

In the upper right, you have the Signal Editor, where you edit the selected channel. The following options are available: In the lower right, you find the Signal Tester that allows you to test the currently selected signal on example data, i.e., to verify that the right values are used for the signal plot. There are three fields in the Signal Tester:

If the signal setup is incorrect for some reason, e.g., an incorrect regular expression, the specific input field turns red.

If you close this window, it can be opened again from the User Event Signal Plot window menu, under "Customize" -> "Signal Setup".

Signal Templates

From the Signal Setup dialog, you can load and save signal setups as tempates for future use using the "Use Tempate" and "Save as Template" buttons. These opens the Signal Templates dialog that displays the templates available in a grid view. The grid view contains one line per template, with the same properties as in the editor, except that color is not a part of the template and there is also an extra field for a description of the template. Note that the name field is the template name, not the signal name, so this is not copied to the Signal Editor when applying the template.

Below the grid view you find three buttons:

You can edit the templates directly in the grid view and the changes are automatically evaluated using the example data and the result is then shown in the Resulting Value column. You may also create a new template here by editing the empty line in the bottom. When editing the cells in the grid view, you need to press ENTER to apply the change. If there is an error in the template (typically the regular expression), the Resulting Value cell of the affected row will turn red.


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