.. program:: ghdl
.. _USING:QuickStart:

Quick Start Guide
#################

Since this is the user and reference manual for `GHDL`, it does not contain an
introduction to `VHDL`. Thus, the reader should have at least a basic knowledge
of `VHDL`. A good knowledge of `VHDL` language reference manual (usually called
LRM) is a plus. Nevertheless, multiple examples are provided, in the hope that
they are useful for users to learn about both `GHDL` and `VHDL`. For advanced
examples using specific features see :ref:`USING:Examples`.

As explained in :ref:`INTRO:GHDL`, `GHDL` is a compiler which translates `VHDL` files to
machine code. Hence, the regular workflow is composed of three steps:

* :ref:`Analysis:command`: convert design units (`VHDL` sources) to an internal representation.
* :ref:`Elaboration:command`: generate executable machine code for a target module (top-level entity).
* :ref:`Run:command`: execute the design to test the behaviour, generate output/waveforms, etc.

The following tips might be useful:

* Don't forget to select the version of the VHDL standard you want to use (see
  :ref:`VHDL_standards`). The default is :option:`--std=93c <--std>`. Use :option:`--std=08 <--std>` for VHDL-2008
  (albeit not fully implemented).

  * Use :option:`--ieee=synopsys <--ieee>` if your design depends on a non-standard implementation of the IEEE library.

  * Use :option:`-fexplicit` and :option:`-frelaxed-rules` if needed.

* Use :option:`--work=LIB_NAME <--work>` to analyze files into the ``LIB_NAME`` library.
  To use files analyzed to a different directory, give the path
  to the ``LIB_NAME`` library using :option:`-P/path/to/name/directory/ <-P<DIRECTORY>>`.

* Use the same options for analysis and elaboration. E.g., first analyse with ``ghdl -a --std=08 --work=mylib myfile.vhdl``;
  and then elaborate and run with ``ghdl --elab-run --std=08 top``.

Due to the fact that `VHDL` is processed as a general purpose language
(instead of an `HDL`), all the language features are to be supported. I.e., `VHDL`
sources do not need to be limited to the synthesisable subset. However, distinction
between synthesisable and non-synthesisable (simulation-only) subsets is often misleading
for users who are new to the language. Different examples are provided,
in the hope of helping understand the different use cases:

.. toctree::

   hello/README
   heartbeat/README
   adder/README
   DLXModelSuite
