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Is this function not supported in ModelSim?? When I compile the altera_mf, I don't see it in the library. Any thoughts?
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There is probably no functional simulation model. altpriority_encoder is used internally in the synthesis of several arithmetic MegaFunctions, but apperently not in the respective simulation models.
But what's the point of simulating altpriority_encoder? For the functional simulation you can replace it by a simple behavioral model as suggested previously in this thread. If you are interested in timing behaviour, you'll refer to gate level simulation.