Open-source simulator for the VHDL language.


Analyze a VHDL source file and produce an object file

$ ghdl -a [filename.vhdl]

Elaborate a design (where {{design}} is the name of a configuration unit, entity unit or architecture unit)
$ ghdl -e [design]

Run an elaborated design
$ ghdl -r [design]

Run an elaborated design and dump output to a waveform file
$ ghdl -r [design] --wave=[output.ghw]

Check the syntax of a VHDL source file
$ ghdl -s [filename.vhdl]

Display the help page
$ ghdl --help


ghdl [command] [options] files...
ghdl-gcc [command] [options] files...
ghdl-llvm [command] [options] files...
ghdl-mcode [command] [options] files...


This manual page documents briefly the ghdl command. This manual page was written for user of man, but is not as complete as the reference documentation.

Instead, users should read the GHDL texinfo manual

The Debian package supports installing multiple GHDL backends at the same time. The GHDL executable ghdl is actually a wrapper that will execute the first installed backend it finds in the order mcode, gcc, llvm. If you want to run GHDL with a specific backend you can directly run their executable, named ghdl-mcode, ghdl-gcc and ghdl-llvm respectively. Alternatively, you can run ghdl with the GHDL_BACKEND environment variable set to mcode, gcc or llvm to select a backend. If the backend in GHDL_BACKEND is not installed or invalid, the wrapper will silently revert to selecting the first installed backend it finds.


This program follows the usual GNU command line syntax, with long options starting with two dashes (`-'). A summary of the main modes and options is included below. For a complete description, refer to the GHDL texinfo manual.

Basic commands:


Analysis, i.e. ghdl -a file.vhdl


Elabortation, i.e. ghdl -e unit_name


Run: run the simulation, i.e. ghdl -r unit_name


Syntax-check, i.e. ghdl -s file.vhdl


Clean: remove generated files, i.e. ghdl --clean

-h, --help

Help, i.e. ghdl --help


Version, i.e. ghdl --version

Basic options:


Name of the WORK library, i.e. ghdl -a --work=foo foo.vhdl


Which VHDL standard (87|93|93c|00|02), i.e. ghdl -a --std=87 old.vhdl


Which IEEE library (none|standard|synopsys|mentor), i.e. ghdl -a --ieee=synopsys broken.vhdl


Disable VITAL restriction checking, i.e. ghdl -a --no-vital-checks unsupported_vital.vhdl

There are many more modes and options; please consult the documentation.

Executables created by GHDL have addition simulation options. The most important ones are listed below:


Show options for simulation and execution.


Assert level at which to stop simulation (none|note|warning|error|failure), i.e. ./touchy_design --assert-level=note


Stop simuation after TIME, i.e. ./design --stop-time=50ns


Dump VCD to FILENAME (a waveform dump, viewable with--for instance--gtkwave), i.e. ./design --vcd=design.vcd


Back annotate SDF onto design using TYPE (min|typ|max), instance PATH, and SDF file FILENAME, i.e. ./sdf_design --sdf=typ=top/inst=inst.sdf


gtkwave(1) The texinfo manual fully documents GHDL. You may also browse it at <>.


This manual page was written by Wesley J. Landaker <>, for the Debian project (but may be used by others). It is released under the same terms as GHDL, i.e. the GNU General Public License. It was modified by Tristan Gingold to include it in the GHDL sources.

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