This back end displays clock evolutions as waveforms. The waveforms are created during the simulation of a CCSL (Clock Constraint Specification Language) specification. It can be visualized step by step in debug mode and is totally interactive for the representation of relations between instants.

Usually, it is configured in the run configuration and created automatically. If you want to visualize an existing VCD, follow these steps.

To open the Viewer, right click on a vcd file and in the menu Open With select Vcd Multi-page Editor

view of the VCD contextual menu

This command opens the VCD file with our editor:

The page Vcd Viewer displays for each clock its name and the associated waveform You can access the textual representation of the VCD in the dedicated tab:


Displaying constraints

The Vcd Viewer can show constraint(s) between two or more clocks. If you put the cursor on a clock instant and if this clock is constrained the viewer displays the relation (textual form) on bottom of the editor. You can also display constraints in the form of arrows simply by clicking on clock instants

Strict precedence

For instance, after a click on the second instant of InWord

To hide constraints, just click again on the same instant.

In this example the top two arrows represent an alternation (relation alternatesWith) between Ready and InWord.

The third arrow linking an InWord instant and the blue rectangle denotes a precedence (relation precedes).

Some examples with other clock constraints follow:

Displaying constraints relies on special comments included in the VCD file.These comments have a strict syntax. See the Comments part for more details.


It is possible to zoom with the combination of Ctrl key and the wheel button or to use the dedicated menu.

Show,hide and move clocks

When you open the VCD Viewer a menu Vcd Editor appears. In this menu selectClock and then Ordering

This dialog box allows you to add, remove and move clocks using arrows. Clocks can also be moved by drag and drop on clock names.


This functionality gives access to a given instant of a clock. To use the find option, click on the Find button in the menu.

Select a clock name and enter the number of the desired instant. After clicking on OK, the instant is highlighted in red.

Ghost Mode


What is it?

The ghost mode is an option allowing the display or hiding of ghost instants. This kind of instant is represented by a filled rectangle.A ghost instant represents a potential instant of the clock (the clock could have ticked at this time, but its actual tick has been postponed).

The button for displaying or hiding ghost instants, is in submenu Options.

With ghosts:

Without ghosts:

Time marker and fireable clocks

The time marker is a vertical red line which appears when you click with the right-button.

The status of a clock under the time marker is reflected in the left part of the figure.

Light green clock names represent ticking clocks (i.e., clock that actually ticks), while dark green clock names represent clocks with a ghost instant


Comments in the VCD file are mandatory for the correct display of constraints Syntax for a comment containing a constraint:

$comment constraint statement $end

Syntax for a comment containing a clock state:

$comment status F clock_ident $end

The best solution for generating a correct VCD file is to use the plug-in CCSL Parser.

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