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I'm learning VHDL at university and we use Xilinx. The professor told us to write a simple 8:1 multiplexer with multiple architecture implementations: structural (using hierarchical design with two 4:1 mux and one 2:1 mux), behavioral (with if-then-else and with case statement) and data flow (with when-else and with-select).

So, I have my 8:1 mux with 5 different architectures in the same VHDL file. Now I need to synthesize each architecture in order to compare the number of IO, the number of BELs and the maximum frequency.

The problem is that I always get the same result, no matter the implementation I choose. I'm sure that I'm making a mistake somewhere in the synthesis process, my hierarchy looks like the one in the attached picture.

Do I have to write something in the file to tell the synthesizer which architecture to use like I've done in the testbench? This is a screenshot of my architecture:

Screenshot of architecture hierarchy

bouteillebleu
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matteof93
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  • [This question](https://stackoverflow.com/questions/29614349/what-happens-when-there-are-multiple-architectures-on-a-single-entity) looks very similar to yours, may be helpful. –  Oct 24 '17 at 10:30
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    Possible duplicate of [What happens when there are multiple architectures on a single entity?](https://stackoverflow.com/questions/29614349/what-happens-when-there-are-multiple-architectures-on-a-single-entity) – JHBonarius Oct 24 '17 at 10:56
  • Also take a look at [the VHDL `configuration` statement](https://www.doulos.com/knowhow/vhdl_designers_guide/configurations_part_1/) – JHBonarius Oct 24 '17 at 10:58
  • There are three ways to provide a binding indication in a component instantiation. A configuration specification supports instantiating a declared component and appears in an architecture declarative part. As the linked question shows when instantiating a design entity you can optionally bind an architecture. There's also configuration instantiation, which may not be supported and requires a configuration declaration for the instantiated entity. Show a [Minimal, Complete and Verifiable example](https://stackoverflow.com/help/mcve) exhibiting a specific problem. –  Oct 24 '17 at 19:24

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