Till KTH:s startsida Till KTH:s startsida

Testbench in ModelSim (en)

en Testbench in ModelSim 

Automate the testing of the code lock

pdf  testbench.pdf

Select the correct software version - in school there are several versions installed in the Start menu!

Altera Web edition\
    ModelSim-Altera Starter Edition\
          ModelSim-Altera 10.1d(Quartus II 13.0sp1)  

Start ModelSim.


Click on Jumpstart This time we choose "Open Project" for continue with our previous MAXsim-project.


In addition to the VHDL code for the lock, we now need another VHDL file for the test bench code.


Create a new empty VHDL-file. Copy and paste the content of the file  tb_lockmall.vhd  and then save the file using the same name,  tb_lockmall.vhd, among the other files in the project.

Alternatively, you can copy the file  tb_lockmall.vhd  to the folder with the other files of the project.

testbench.gif  tb_lockmall.vhd   ( text.gif tb_lockmall.txt )

Add the VHDL-file to the project



The project now has two files. The file  tb_lockmall.vhd  is not compiled yet, which can be seen on the blue question mark.


Choose the menu Compile and the alternative Compile All. Now the file is compiled  tb_lockmall.vhd. By the content of the file we can see that it controles the other file  codelock.vhd, so that's why it gets the highest order.


Load the Design to the simulator.

We want to test the bench messages to appear (as arrows) at the top of the Wave-window. 
Therefore, we write in the Transcript window:

NOTE ! Important to get the arrows!

vsim -msgmode both -displaymsgmode both tb_codelock

Then add the signals in the Wave-window.

add wave *

Start simulation

In the file  tb_codelock.vhd  you find  clk <= not clk after 10 ns;. It creates the clock pulses with a period of 20 ns, as we used before.


We can immediately start the simulation with the command run 3us in the Transcript-window. The time 3 μs sufficient to try all possible key-press combinations.

run 3us

In the Transcript-window we can read the encouraging message  Note: Lock tries to open for the right sequence!. 
In Wave-window choose ViewZoom, and Zoom Full and then you can see the entire process.  (Zoom Last  can also be usefull).


The green arrows show the when the desired event happens! 
Now exit the simulation.

endsimulation.gif endsimulationyes.gif

Reveal the wrong code!


Now we need to in Project window, double-click the file  codelock.vhd  so that it appears in the text editor where we can change it. Copy and paste the content of the file  lockmall_with_error.vhd. Then save the file under the same name as before and recompile everything.

vhdlfile  lockmall_with_error.vhd   ( text.gif lockmall_with_error.txt )

Simulate in the same way as before. In Transcript-window you can read the message from the test bench when event happens!

The red arrow in the Wave-window shows  when/where  the undesired event happens!


VHDL-test bench file

You do not of course be able to write a VHDL Test Bench file after a short first course on Digital Design. Still take the opportunity to go through the file and see if you can understand how it is intended!