Waveform Viewer - CMU-18240/240-How-to GitHub Wiki

The waveform viewer is an extremely useful tool for debugging your design. While you may be tempted to rely solely on $display statements for debugging, it cannot be stressed enough that you should use the waveform for debugging. It may not be absolutely necessary for extremely simple designs, but once you get to more complex ones with many signals you should use the waveform.

If you find yourself stuck when debugging, and you haven't tried the waveform viewer you should try the waveform viewer. Otherwise you won't get much sympathy from the TAs.

It is worth noting that if you are SSHing then you will need to set up X11 forwarding.

Compile with the debug flag

vcs -sverilog -debug <filename>.sv

Execute with the -gui flag

./simv -gui &

To compile and start the waveform viewer:

vcs -sverilog -gui -R <filename>.sv

This starts up a GUI interface to the simulator, known as DVE (Discovery Visual Environment).

• Shows the different modules of your design and how they are nested within each other
• Expand by clicking the little plus sign
• Select a module by clicking on it

• Shows the names and types of all signals defined in a selected module
• Highlight multiple signals by holding the CTRL key
• Highlight all signals with CTRL+A

• Displays SystemVerilog file
• Expand modules by clicking the little plus sign
• This is not a text editor. You can’t change your SystemVerilog file in this window

• Displays simulation output
• You can run the simulation in any of the following ways:
  • Click Simulator → Start/Continue
  • Press F5
  • Press the blue down arrow in the top left corner

1. Highlight the signals in the Data Pane that you want displayed.
2. Click Signal (or right click in data pane) → Add to Waves → New Wave View
3. Run the simulation in any of the mentioned three ways

It may be easier in some cases to recompile your code from within the waveform viewer without having to open it with a new executable compiled externally.

1. Click Simulator → Rebuild and Start.
2. In the popup window titled "Simulation Setup," check the "Custom command" option
3. Enter your compilation command in the custom command box, which is likely of the form: vcs -sverilog -debug <filename>.sv
4. Either use the "Browse" button or type the directory you wish this command to be run in. Ensure that the filenames/paths in step 3 are relative to this directory.
5. Ensure the Action on OK option is set to "Rebuild and Start" and click "OK."
6. You will receive compilation messages at the bottom of the primary DVE window. After compilation completes, you can execute the new simulation.

You may find it irritating to have to close the waveform viewer, recompile your code, and read the signals you were looking at. Thankfully you can save the set of signals viewed on the waveform viewer to load later.

1. On the waveform viewer window (not the DVE window with the individual panes), click File → Save Session.
2. This will create a .tcl file. Name it to something appropriate and put it somewhere where you can find it later.
3. The next time you open up DVE (i.e. after recompiling), simply click File → Load Session, and open up that .tcl file you saved.

• To add more signals to the Wave View, highlight the desired signals and right click → Add to Waves → Add to Wave #
• Zoom in and out on the waveform by holding the CTRL key and using the +/- keys
• For multibit signals, you can change the display from hex to decimal by right clicking the signal → Set Radix → Decimal. Note that the "Decimal" radix is signed, so if you want unsigned you should set the radix to "Unsigned".
• To edit SystemVerilog in the Waveform Viewer, right click in the Source Pane → Edit Source and a separate terminal window will open up your sv file.