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Perhaps a better question would be where would I use signal spy and where would I be better of trying to force signals?
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A better method is to create a testbench that models the inputs and checks the outputs for the entity being tested. Then you don't need to force signals at all, nor do you necessarily need to bring out internal signals for monitoring since you can have assertion checking that the top level outputs are producing the correct results. Lower level blocks are tested with their own testbench to verify correct operation. My $0.02
Kevin Jennings
Honored Contributor
