Support for GHDL Synthesis

[sigmuha]

This is a feature request for supporting the --synth flag in ghdl.

As I understand it, the current ghdl.a_flags, ghdl.elab_flags, and ghdl.elab_e compilation options aren't sufficient to support this feature. Please correct me if I'm wrong...

There are two different syntaxes that are available, where the first one might be preferred, as all libraries may be dumped with a -Pflag, and the top modules may be specified with --work=, and --worklib=:

--synth <[options...] [library.]top_unit [arch]>
--synth <[options...] file... -e [top_unit [arch]]>

This would be a great feature to add, as it may be used as a quick check before synthesis in a vendor tool to save time, or as a converter to VHDL 93, enabling the usage of 2019 features, even though the vendor tool doesn't support it etc.

[LarsAsplund]

To limit the scope of VUnit we have decided not to expand beyond simulation. The exception has been some Vivado script but that was an early "mistake".

It's still possible to use VUnit as a starting point. I did it myself in a previous project. Basically you can let a run script setup and compile the project. I'm not sure what the status is now but it used to be that GHDL synth was limited to VHDL-93.

Rather than ending the script with a call to the VUnit main function, you can do something like this:

    try:
        vu.main()
    except SystemExit as exc:
        if exc.code != 0:
            sys.exit(1)
``´

As long as VUnit doesn't encounter any problems, the script will continue such that you can use call Yosys/GHDL synth and let them use the libraries compiled by the VUnit part of the script.