Simulate and view waveforms in VHDL without a test bench

[Arvind Gupta]

Hi,

  I ma new to EDA Playground and  find this concept amazing. I have a few queries related to your online platform.

I plan to make a series of tutorials on VHDL for the beginners where they will write small codes and simulate them to see the waveforms (such as logic gates, adders mux etc). Acordingly, I wanted to know if I can run a simulation and view waveforms without having to write its test bench? Something like forcing the inputs to particular values at the waveform viewer interface or somewhere else. The reason for asking is that initially, the beginners may find it difficult to write test benches.

Secondly, I wanted to know if I can use EDA Playground as a tool to create tutorials and host the tutorials on a website? Does one need any specific permissions to do so? If yes, pls elaborate.

Looking forward to your answers.

Thanks,

Arvind Gupta. 

[EDA Playground]

It's great that you would like to use EDA Playground. To answer your questions:

Whether or not it is possible to generate input stimulus without a testbench depends on the simulator, not on EDA Playground per se. So, I am assuming you would create your stimulus in a file (in some format or other) and issue some command to the simulator to read that file as input stimulus. (You can create files by clicking on the "+" at the top of the testbench and design panes.) You would probably also need to create a TCL file (the same way as you created the stimulus file) which contains the command that reads the stimulus file and then you would have to select "Use run.do" (on the left hand side of the EDA Playground screen). This all sounds more complicated that writing a testbench to me, but that's up to you.

Please do link to EDA Playground from your tutorials and/or host them on EDA Playground. 

[Arvind Gupta]

Hi,

   Thanks for the response.

   Yes you are right. Writing TCL files with the stimuli will be equally difficult for new comers. Consider that I want to simulate a 2-input AND gate. Let the inputs be ‘A_in’ & ‘B_in’ and the output be ‘C_out’. Accordingly, I am looking for either of the following:

 

 ** As in Xilinx ISE (eg. ver. 10.1) where one can toggle the input waveforms A_in and B_in to generate all the four input cases (00, 01, 10, 11). Then run the simulation and view the waveforms for both the inputs and the expected output.

 ** As in Modelsim (eg. Student edition), where after opening the simulation window, one can right click on an input value (A_in and B_in in this case) and select the ‘Force’ option to enter the input string (For eg: A_in as ‘0011’ and B_in as ‘0101’). Then click the ‘Play button’ to watch the output waveform as per the input waveform cases.

 

 Also, pls note that I am OK with using any simulator as long as it is free to use at your website.

 

Looking forward your reply.

Regards,

Arvind Gupta. 

[EDA Playground]

The interface to the EDA tools on EDA Playground is almost entirely text-based, ie TCL, bash or command options. I'm afraid that there is nothing built into EDA Playground to allow one to generate input stimulus in the way that you say Modelsim and ISE do it. I can't imagine we'd ever invest time in implementing such a thing: we teach our customers to write testbenches. Perhaps you could write a testbench or a TCL script that read a text file, which has some simple format which your students could edit?