ModelSim SE User's Manual - Electrical and Computer Engineering

UM-306 11 - Tracing signals with the Dataflow window
Tracing events (causality)
ModelSim SE User’s Manual
One of the most useful features of the Dataflow window is tracing an event to see the cause
of an unexpected output. This feature uses the Dataflow window’s embedded wave viewer
(see "The embedded wave viewer" (UM-304) for more details).
In short you identify an output of interest in the Dataflow pane and then use time cursors in
the wave viewer pane to identify events that contribute to the output.
The process for tracing events is as follows:
1 Log all signals before starting the simulation (add log -r /*).
2 After running a simulation for some period of time, open the Dataflow window and the
wave viewer pane.
3 Add a process or signal of interest into the Dataflow window (if adding a signal, find its
driving process). Select the process and all signals attached to the selected process will
appear in the wave viewer pane.
4 Place a time cursor on an edge of interest; the edge should be on a signal that is an output
of the process.
5 Select Trace > Trace next event.
A second cursor is added at the most recent input event.
6 Keep selecting Trace > Trace next event until you've reached an input event of interest.
Note that the signals with the events are selected in the wave pane.
7 Now select Trace > Trace event set.
The Dataflow display "jumps" to the source of the selected input event(s). The operation
follows all signals selected in the wave viewer pane. You can change which signals are
followed by changing the selection.
8 To continue tracing, go back to step 5 and repeat.
If you want to start over at the originally selected output, select Trace > Trace event reset.