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Questasim optimization

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Binome

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Hi,
when simulating my design with no optimization I can see one of the output signals changing from 0 to 1 then back to 0. When simulating with optimization this signal is deleted and I don't understand why. Is there a way to know? (An ISE synthesis doesn't show any error or warning. I can't publish my vhdl code because it's too long and because of property.)
Thanks for any help.
 

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Hi,
when simulating my design with no optimization I can see one of the output signals changing from 0 to 1 then back to 0. When simulating with optimization this signal is deleted and I don't understand why. Is there a way to know? (An ISE synthesis doesn't show any error or warning. I can't publish my vhdl code because it's too long and because of property.)
Thanks for any help.

Do you mean the signal no longer shows up as a signal in the design after optimization? If so that is the point of optimization it disables logging of signals you have no interest in. If you need to see that signal then disable optimization of that specific signal. Not entirely sure it's possible to do it to only one signal but you can add +acc=npr+<module_with_signal>+<another_module> to disable optimization for specific modules.
 

Binome

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If so that is the point of optimization it disables logging of signals you have no interest in.

I know that but it is an output port so I don't understand why Questa is considering it as not useful.

I won't disable the optimization for a specific signal because I'm using a GUI version on Windows so I'll use the general "no optimization" option. And I'll try a synthesis to look at this signal.
Thanks anyway.
 

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It's OK for the synthesis with ISE. The pin is available.
 

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I know that but it is an output port so I don't understand why Questa is considering it as not useful.

I won't disable the optimization for a specific signal because I'm using a GUI version on Windows so I'll use the general "no optimization" option. And I'll try a synthesis to look at this signal.
Thanks anyway.

It's not a mater of usefulness of the signal, enabling optimization is to reduce the overhead of keeping the state of all signals visible. The p in that +acc=npr is for ports, so when optimization is enabled even ports disappear.
 

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