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VHDL dependency analyzer and simulation driver.

Project description

vhdeps: a VHDL file dependency analyzer and test runner

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Whatever tool you use, testing VHDL code has always been a pain. With most tools you have to write TCL scripts for compilation, requiring you to copypaste all the paths of the files your test case depends on... eventually leading you to just include everything despite the additional compilation time. Automated testing for CI requires yet more TCL scripting, or is outright not possible due to licensing or the tools being primarily GUI-oriented. Not to mention doing all this for more than two or three integration tests, unit tests be damned. Don't even start about code coverage.

vhdeps aims to change this, at least for a common subset of problems. With it, running your test suite is as simple as going to your project's root directory and running vhdeps ghdl, vhdeps vsim, or whatever other target that may be added in the future. As it should be!


vhdeps is a Python package. To install it, simply run:

sudo pip3 install vhdeps

You can of course install it to a venv or your home directory as well if you prefer, as long as you make sure you add the bin folder to your system path, or call vhdeps using python3 -m vhdeps.

We have only tested vhdeps on Linux and MacOS thus far, but there should not be any fundamental issues with making it work on Windows as well.

Installing vhdeps this way takes care of all its Python dependencies, but does not install ghdl or a vsim-compatible simulator (like Modelsim) for you.

To use the code coverage features of the GHDL target, you must get yourself a GHDL build that uses the GCC backend, and install lcov in addition if you want the fancier output formats.

Once you have that, try the vhlib repository to see vhdeps in action.


After vhdeps determines the compile order for your project, it passes it to a so-called target of your choosing. Currently, the following targets are available.


This target simply dumps the compile order in a format that should be easy to read using whatever script you may devise on your own. It does not require any non-Python tools.

$ vhdeps dump StreamBuffer -o order
Including the current working directory recursively by default...

$ cat order
dep work 2008 /path/to/vhlib/stream/StreamSlice.vhd
dep work 2008 /path/to/vhlib/util/UtilRam1R1W.vhd
dep work 2008 /path/to/vhlib/stream/StreamFIFOCounter.vhd
dep work 2008 /path/to/vhlib/util/UtilRam_pkg.vhd
dep work 2008 /path/to/vhlib/util/UtilInt_pkg.vhd
dep work 2008 /path/to/vhlib/stream/Stream_pkg.vhd
dep work 2008 /path/to/vhlib/stream/StreamFIFO.vhd
top work 2008 /path/to/vhlib/stream/StreamBuffer.vhd


This target runs the test cases detected in the compile order using GHDL. For example:

$ vhdeps ghdl StreamBuffer_*_tc
 * PASSED  work.streambuffer_0_tc
 * PASSED  work.streambuffer_200_tc
 * PASSED  work.streambuffer_2_tc
 * PASSED  work.streambuffer_4_tc
 * PASSED  work.streambuffer_6_tc
Test suite PASSED

Here's some of the features this target supports:

  • Runs in a temporary directory by default, preventing .cf or object files from appearing all over the place.
  • Supports parallel elaboration and execution (parallel analysis is not supported by GHDL).
  • Can output VCD files for all test cases to a directory of your choosing.
  • Can automatically open gtkwave for you to view the waveform(s).
  • If GHDL is built with the GCC backend, it can generate coverage information for you, all the way to user-friendly HTML output.


This target runs the test suite in Modelsim or Questasim, either in GUI or batch mode, or simply outputs an appropriate .do file for you. Here's an example of what it all looks like:

$ vhdeps vsim StreamBuffer_*_tc
# Summary:
 * PASSED  work.streambuffer_0_tc
 * PASSED  work.streambuffer_200_tc
 * PASSED  work.streambuffer_2_tc
 * PASSED  work.streambuffer_4_tc
 * PASSED  work.streambuffer_6_tc
Test suite PASSED

$ vhdeps vsim StreamBuffer_0_tc --gui

(after zooming in to the waveforms only:)

Modelsim screenshot

The TCL script supports the following, among other things:

  • Incremental recompilation and rerunning in the GUI through the rerun command.
  • rerun maintains your waveform view configuration (zoom level, signals, etc.).
  • By default, all signals in the toplevel test case entity and all its immediate instantiations are added to the waveform view, and all signals in the design are logged. Inputs are colored blue, outputs are colored yellow, and internal signals are colored white to improve readability. This behavior can be overridden with --pragma vhdeps vsim wave-config-tcl <do file> and --pragma vhdeps vsim no-log-all pragmas in the test case file if desired.
  • When there are multiple test cases, the script executes all of them initially without displaying any waveforms. You can then run debug to run (one of) the failing test case(s) with waveforms enabled to debug it.
  • Automatic GUI vs. batch mode detection. In batch mode, Modelsim automatically exits with 0 or 1 depending on the result of the test suite.

The script is only tested in Modelsim and Questasim so far, and requires some rather magical constructs to make signal coloring and restoring the waveform view work properly. Your mileage may vary with other vsim-compatible tools such as Riviera.

(your target here?)

It's easy to add a new target to vhdeps. Simply look for its install directory (or clone this repository and install it using and add a file to the vhdeps/target directory. vhdeps automagically detects the available targets, so there's no need to add your target to any kind of index.

API documentation is still somewhat lacking, however. Then again, it shouldn't be too difficult to figure it out from the docstrings and existing targets.

VHDL code requirements

vhdeps is currently quite simplistic in its VHDL parsing -- it just uses regular expressions to match entity, component, and package declarations, uses, and definitions and works from there -- but it should be enough for most use cases. Some known limitations are listed here.

By default, vhdeps detects test cases by looking for toplevel entities that end in _tc. This is intentionally different from the industry-standard _tb, because test benches are rarely built to check themselves and self-terminate in practice, which would just lead to timeouts. You can of course adjust this behavior using command-line options. Currently, vhdeps does not support defining multiple test case entities in a single file, but it should be able to handle this just fine for design files.

By self-terminating, we mean that it either terminates by event exhausting to indicate success (usually, this means stopping the clock), or through a severity failure report or assertion statement to indicate failure. If a test case does not terminate within a specified timeout, the test case is also considered to have failed. This timeout is specified in the test case file using a pragma, like this:

-- pragma simulation timeout 10 ms

The timeout arbitrarily defaults to 1 ms if it is not specified.

vhdeps can handle input from different VHDL versions within a single run (as long as the target supports this as well) and can distinguish between simulation-only, synthesis-only, and universal source files. It does this based on tags specified in the VHDL filenames:

  • Filenames matching *.<version>.*, where <version> is a two-digit VHDL version code (93, 08, and so on), are compatible with the specified version. Multiple version tags can be chained for files that are compatible with multiple versions. If no version tag is present, the file is assumed to be compatible with all versions.
  • Filenames matching *.syn.* are synthesis-only.
  • Filenames matching *.sim.* are simulation-only.

You can even have both a VHDL-93 and a VHDL-2008 file for a single design unit; vhdeps will automatically disambiguate based on a desired or required VHDL version that you specify on the command line.

Miscellaneous features

Black box detection

Most tools are, annoyingly, perfectly okay with black boxes by default (black boxes are component instantiations that don't resolve to any previously compiled entity, in case you're not aware). vhdeps isn't: by default, it will refuse to output a compile order for you if your design has black boxes. You can override this behavior by including the files that contain the black box component definitions with the -x flag instead of -i, which may be useful for getting the compile order for projects that use vendor primitives.

Style checking

In addition to the rules above, vhdeps can enforce some additional rules for you if you like by including VHDL files "strictly" (-I instead of -i). These rules are:

  • Each VHDL file must define exactly one entity or exactly one package.
  • VHDL package names must use the _pkg suffix.
  • The filename must match the name of the VHDL entity/package.


Pull requests are welcome. Before opening a PR, check that all tests succeed (or are skipped due to missing dependencies, if they're not relevant to your PR) and that pylint is happy:

$ ./ test
OK (SKIP=...)

$ ./ lint
Your code has been rated at 10.00/10

You can check your code coverage offline as follows:

$ coverage html
$ xdg-open htmlcov/index.html

Once you open your PR, Azure will also check it for you.

We strive to use GitHub flow.

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