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# GHDL
This directory contains the sources of GHDL, the open-source compilator and simulator for [VHDL](https://en.wikipedia.org/wiki/VHDL), a Hardware Description Language ([HDL](https://en.wikipedia.org/wiki/Hardware_description_language)). GHDL is not an interpreter: it allows you to analyse and elaborate sources to generate machine code from your design. Native program execution is the only way for high speed simulation.
## Main features
Full support for the [1987](http://ieeexplore.ieee.org/document/26487/), [1993](http://ieeexplore.ieee.org/document/392561/), [2002](http://ieeexplore.ieee.org/document/1003477/) versions of the [IEEE](www.ieee.org) [1076](http://standards.ieee.org/develop/wg/P1076.html) VHDL standard, and partial for the latest [2008](http://ieeexplore.ieee.org/document/4772740/) revision.
Partial support of [PSL](https://en.wikipedia.org/wiki/Property_Specification_Language).
By using a code generator ([LLVM](http://llvm.org/), [GCC](http://gcc.gnu.org/) or, [x86_64](https://en.wikipedia.org/wiki/X86-64)/[i386](https://en.wikipedia.org/wiki/Intel_80386) only, a built-in one), it is much faster than any interpreted simulator. It can handle very large designs, such as [leon3/grlib](http://www.gaisler.com/index.php/downloads/leongrlib).
GHDL runs on [GNU/Linux](http://en.wikipedia.org/wiki/Linux_distribution), [Windows](http://en.wikipedia.org/wiki/Microsoft_Windows) and [macOS](http://en.wikipedia.org/wiki/MacOS), both on `x86` and on `x86_64`. You can freely download a binary distribution for your OS, or try to build it on your own machine (see *'Getting GHDL'* below).
Can write waveforms to a [GHW](http://ghdl.readthedocs.io/en/latest/using/Simulation.html?highlight=GHW#cmdoption-wave), [VCD](https://en.wikipedia.org/wiki/Value_change_dump) or FST file. Combined with a [GUI](http://en.wikipedia.org/wiki/Graphical_user_interface)-based [waveform viewer](https://en.wikipedia.org/wiki/Waveform_viewer) and a good text editor, GHDL is a very powerful tool for writing, testing and simulating your code.
Supported third party projects: [VUnit](https://vunit.github.io), [OSVVM](http://osvvm.org), [cocotb](https://github.com/potentialventures/cocotb) (through the [VPI interface](https://en.wikipedia.org/wiki/Verilog_Procedural_Interface)), ...
GHDL is free software:
- [](https://github.com/tgingold/ghdl/blob/master/COPYING)
- Doc is available on [ghdl.readthedocs.org](https://ghdl.readthedocs.org/en/latest/index.html).
- Some of the runtime libraries, are under different terms; see the individual source files for details.
## Getting GHDL
### Pre-built releases
You can download pre-built releases for different platforms, backends and library versions from [GitHub releases](https://github.com/1138-4EB/ghdl/releases).
### Building GHDL
You need the GNU Ada compiler, GNAT GPL, 2014 (or later) for x86 (32 or 64 bits). GNAT GPL can be downloaded anonymously from libre.adacore.com. Then, untar and run the doinstall script.
*Depending on the OS and distribution you are using, you will also need to install some toolchain dependencies, such as `zlib`. See '[Building](http://ghdl.readthedocs.io/en/latest/building/index.html)' for specific package names.*
In the GHDL base directory, configure and build:
```sh
$ ./configure --prefix=/usr/local
$ make
```
At that place, you can already use the 'ghdl_mcode' built in the directory. You can also install GHDL:
```sh
$ make install
```
That's all!
*The executable is installed as 'ghdl' in `/usr/local`. To install it to a different path, change the `--prefix` in the call to `configure`. For example, on Windows, you may want to set it to `--prefix=/c/Program Files (x86)/GHDL`.*
---
Furthermore, each supported compiler has its pros and cons. Here is a short comparaison:
| | pros | cons | observations |
|---|---|---|---|
|mcode | very easy to build | x86_64/i386 only | no executable created from your design |
| | very quick analysis time and can analyze very big designs | simulation is slower | |
| GCC | generated code is faster | analyze can take time (particularly for big units) | the output is an executable |
| | generated code can be debugged | build is more complex |
| | many platforms (x86, x86_64, powerpc, sparc) | |
LLVM has the same pros/cons as GCC, but it is easier to build. However, coverage (`gcov`) is unique to GCC.
You can find specific instructions for each of the options in '[Building](http://ghdl.readthedocs.io/en/latest/building/index.html)'.
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