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.. program:: ghdl
.. _USING:QuickStart:Simulation:
Simulation
##########
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. For instance,
if you would like to use VHDL 2008 and also use shared variables with an
ordinary type (deprecated in VHDL 2000), you can use ``--std=08 -frelaxed-rules``.
* 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>`.
* 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/index
heartbeat/index
adder/index
DLXModelSuite
.. TIP:: See :ghdlissue:`Learning VHDL with GHDL <1291>`.
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