Other co-simulation projects

This section contains references to other co-simulation projects based on GHDL and VHPIDIRECT.

ghdlex and netpp

netpp (network property protocol) is a communication library allowing to expose variables or other properties of an application to the network as abstract ‘Properties’. Its basic philosophy is that a device always knows its capabilities. netpp capable devices can be explored by command line, Python scripts or GUI applications. Properties of a device - be it virtual or real - are typically described by a static description in an XML device description language, but they can also be constructed on the fly.

ghdlex is a set of C extensions to facilitate data exchange between a GHDL simulation and external applications. VHPIDIRECT mechanisms are used to wrap GHDL data types into structures usable from a C library. ghdlex uses the netpp library to expose virtual entities (such as pins or RAM) to the network. It also demonstrates simple data I/O through unix pipes. A few VHDL example entities are provided, such as a virtual console, FIFOs, RAM.

The author of netpp and ghdlex is also working on MaSoCist, a linux’ish build system for System on Chip designs, based on GHDL. It allows to handle more complex setup, e.g. how a RISC-V architecture (for example) is regress-tested using a virtual debug interface.


VUnit is an open source unit testing framework for VHDL/SystemVerilog. Sharing memory buffers between foreign C or Python applications and VHDL testbenches is supported through GHDL’s VHPIDIRECT features. Buffers are accessed from VHDL as either strings, arrays of bytes or arrays of 32 bit integers. See VUnit/cosim for details about the API.


Yann Guidon is a many-hack who tried to push GHDL’s VHPIDIRECT over the edge in a series of articles around 2010 (as you can read this, GHDL recovered very well since).

GHDL is an essential tool to design Free HW designs and Yann is still trying to hack it beyond its intended scope, to fill voids in the Free Software landscape that keep him from designing more microprocessor cores. He is mostly active on Hackaday.io (hackaday.io/whygee) and working on converging projects such as: