Timing Simulation

Timing simulation uses the block and routing delay information from the routed design to give a more accurate assessment of the behavior of the circuit under worst-case conditions. For this reason, timing simulation is performed after the design has been placed and routed.

This section of the tutorial shows how to run a script to do a simulation. Timing simulation uses the same tools as does the functional simulation that you did with the design earlier. The only difference is that the design which is loaded into the simulator for timing simulation contains worst-case routing delays based on the actual placed and routed design.

Invoking Timing Simulation

To invoke the timing simulator, click the Timing Simulation icon in the Verification phase button in the Project Manager Flow diagram.

The simulator is now loaded and ready to simulate. For this simulation, you will use an existing script file.

Simulating with Script Files - Script Editor

Earlier, you used the Foundation Series functional simulator to input signals to the simulator and to provide stimulus including keyboard stimulus and the internal binary counter. In this section, you use a script file to simulate the design and will launch it from the Script Editor.

1. To invoke the Script Editor, select Tools Script Editor from the pulldown menus within the Simulator. A dialog box prompts you to select a script file.
   
   
2. Choose Open: Existing Script File and click OK.
   
   
3. Select the file: jcount.cmd, which was written previously for you to use in this tutorial.
   
   

Browse the script file; you will notice the same inputs and outputs that you used in the functional simulation earlier.

Running the Simulation from the Script Editor

1. You can execute the simulation directly from the Script Editor. To do this, select Execute Go.
   
   A log of the executed commands appears at the bottom of the Script Editor.
   
   
2. To view the simulation results in the Waveform Viewer, move the Script Editor window and bring the Waveform Viewer window to the front of your view.
   
   
3. Click the Expand icon located above the signal names display to view the waveform in more details.
   
   
   
   
4. Inspect the simulation results to make sure they are accurate.
   
   

You should now see that this is indeed performing a timing simulation based on actual delays in the placed and routed design. If you zoom in to get a closer view of the waveforms, you will see that there is a delay from the rising edge of the clock to the transitions or the counter outputs.

Figure 3.25 Timing Simulation Waveforms

Closing the Simulator

When you are satisfied with the results of the simulation, you may close the Script Editor and the Simulator.