Why simulation results differ between quartus & modelsim

Hi everybody!

Could someone please explain to me why a simulation that is correct in altera quartus isn't in modelsim?

I have quartus 7.2 web ed. and modelsim 6.2b (NOT altera version).
I ran a simulation based on a waveform file i created in quartus and then i exported the report to a verilog test file (*.vt)

I loaded the test file into modelsim and ran the vector_test and it didn't succed. I tried both functional and timing tests.

I also tried to code my own testbenches but none of them worked.

Is it because quartus is using specific device characteristics like gate delays etc. and modelsim doesn't?

Thanks in advance!

Re: Why simulation results differ between quartus & mode

none of them worked

Click to expand...

That could mean a lot of different things, you can't actually expect a specific answer on that question?

You are right in so far, as the Quartus simulator is nearer to a gate level simulation, even in functional mode, as far as I understand. Modelsim in contrast is interpreting the HDL code, sometimes using slightly different rules than a synthesis tool. This is obvious with some unsynthesisable HDL constructs that may seem meaningful in ModelSim. Some (bad) HDL constructs cause partly unpredictable behaviour, that may depend e. g. on the order of code evaluation.

For a more specific answer, you should show a duplicatable example.

Re: Why simulation results differ between quartus & mode

Well i think i found it.
There is a way to simulate in modelsim at a gate level. All i had to do is to properly set the EDA Tool in quartus.
In this way quartus copies all the necessary libraries which contain the device properties to modelsim.
Then by choosing run eda gate level simulation in quartus, modelsim launches automatically and works the same way that quartus simulator does.

The results are the same now. Yuppie!!


Now this allows you to write an hdl testbench and simulate it at gate level just like you would with quartus' waveforms.
But it's a lot more easier and quicker to write a testbench than drawing waves...

Here's a quick video tutorial by altera on how to do all the above:
Set up quartus to work with modelsim (use IE..won't open with firefox).
Depending on your software edition the steps could be slightly different but if you're interested you'll find the way out...

Thanks ...