Modelsim Assert

[RishiD]

Hi,

I am still trying to learn how to create good test benches. Is it
possible to have modelsim to like give a warning when two of my signals
equal each other? Basically I want to run through my simulation, but
not go through all the wave forms to see if this error occurs. I
believe assertions are the way to go, but have never used them before.
Anyone point me to a tutorial of some sorts?

Thanks,

RishiD

 

[ghelbig]

The assert statement is much preferred over manually checking timing
diagrams. That's what they're there for.

You're looking for something like this:

assert Signal_1 = Signal_2
report "Signal_1 equals Signal_2"
severity warning;

Or better yet, try this link:
<http://www.google.com/search?hl=en&q=vhdl+assert&btnG=Google+Search>

 

[RishiD]

Ah thanks, kept searching "Modelsim assert". Thinking it was a
modelsim thing.

Thanks for the help.

 

[KJ]

The assert statement is much preferred over manually checking timing
diagrams. That's what they're there for.

You're looking for something like this:

assert Signal_1 = Signal_2
report "Signal_1 equals Signal_2"
severity warning;

Minor problem. The original post asked "Is it possible to have modelsim to
like give a warning when two of my signals
equal each other" which means that what needs to be asserted is that the two
signals are NOT equal to each other so that the warning pops up when the two
signals ARE equal to each other.

assert Signal_1 /= Signal_2 -- or assert not(Signal_1 = Signal_2),
whichever floats your boat
report "Signal_1 equals Signal_2"
severity warning; -- typically I would use 'error' here instead
of 'warning' since it probably is a design error that needs fixing

When using an assert you specify the condition that is supposed to be true
so that when/if that condition is found to not be true the warning is
printed.

KJ

 

[Ajeetha]

Hi Rishi,
As others have pointed out, VHDL's assert will do this easily. But
there's lot more you can do with a specialized assertion language such
as PSL (with VHDL flavor) or SVA. I wrote a PSL tutorial some time
back, see: www.project-veripage.com

HTH
Ajeetha, CVC
www.noveldv.com

 

[ghelbig]

"I left that as an exercise for the student."

"I code them upside down on purpose to test the bench."

Seriously, thanks for the correction.

GH