Getting started

The modules can be used straight away in your simulation and build project. Start by cloning the repo:

If you want a stable release you can checkout one of the tags.

Source code

Synthesizable source code is found in the src folder of each module. These files should be added to your simulation and build project. The library name is the same as the module name.

Test code is found in the test folder of each module. Simulation code (BFMs) is found in the sim folder of each module. The simulation code should be added to your simulation project.

All files must be handled as VHDL-2008.


When using tsfpga, this is done with a call to tsfpga.module.get_modules() and appending to your current list of modules.

Scoped constraints

Many entities in this project have corresponding constraint files that must be used in build projects for proper operation. These are found in the scoped_constraints directory of the module, which contains .tcl files that have the same file name as the corresponding entity.

These must be loaded in Vivado with e.g.

read_xdc -ref asynchronous_fifo /home/lukas/work/repo/hdl-modules/hdl-modules/modules/fifo/scoped_constraints/asynchronous_fifo.tcl

The constraint file being scoped means that it is applied relative to each instance of the entity. Using this we do not have to search through the whole design hierarchically to find the signals that we are interested in in our constraint file.


When using tsfpga, this is done automatically for build projects, since hdl-modules uses the recommended module structure.

Unresolved types

The modules consistently use unresolved types (e.g. std_ulogic instead of std_logic, u_unsigned instead of unsigned, etc.). This means that accidental multiple drivers of a signal will result in an error when simulating or synthesizing the design.

Since e.g. std_logic is a sub-type of std_ulogic in VHDL-2008, it is no problem if hdl-modules components are integrated in a code base that still uses the resolved types. E.g. a std_logic signal can be attached to a hdl-modules port of type std_ulogic (both in and out) without problem.


If you find any bugs or inconsistencies, please start a discussion or create an issue on GitHub.