USER LIBRARIES (Quartus II 5.1/7.2)

For Quartus to find a file in the library directory, the filename must match the entity name inside the file.

I think two entities with the same name was the situation for which I filed an enhancement request quite a while ago. I vaguely recall that the change has been made by version 7.2, but I don't know remember the details and so don't know whether it covers your situation. It might have been a case where two different VHDL libraries contained the same entity (not quite the same thing as a Quartus user library).

You can have multiple entities with the same name, they just need to be compiled into different libraries. You can set the library when you add the source file to the project; otherwise, all the stuff in the file will be compiled into the "work" library. The Quartus II Handbook has all the gory details!

Auto-discovered entities are another matter. They automatically go into the "work" library. Also, Quartus II searches the user libraries in order. It stops when it finds a file called target_entity_name.{v,vhd,vhdl,etc} that contains a declaration for the target entity. You can have duplicates in your user libraries, but only one will ever be used based on the search order. I don't like auto-discovery of source files. It's a lazy feature and probably causes more grief than good. I highly recommend adding all your source files to the project explicitly.

Thank you all!

I think I solved my problem thanks to yor advices!

All the best,

Paola