testbed/cocotb__cocotb/docs/source/building.rst

.. _building:

***************************************
Build options and Environment Variables
***************************************

Make System
===========

Makefiles are provided for a variety of simulators in :file:`src/cocotb/share/makefiles/simulators`.
The common Makefile :file:`src/cocotb/share/makefiles/Makefile.sim` includes the appropriate simulator Makefile based on the contents of the :make:var:`SIM` variable.

Make Targets
------------

Makefiles defines the targets ``regression`` and ``sim``, the default target is ``sim``.

Both rules create a results file with the name taken from :envvar:`COCOTB_RESULTS_FILE`, defaulting to ``results.xml``.
This file is a xUnit-compatible output file suitable for use with e.g. `Jenkins <https://jenkins.io/>`_.
The ``sim`` targets unconditionally re-runs the simulator whereas the ``regression`` target only re-builds if any dependencies have changed.

In addition, the target ``clean`` can be used to remove build and simulation artifacts.
The target ``help`` lists these available targets and the variables described below.

Make Phases
-----------

Typically the makefiles provided with cocotb for various simulators use a separate ``compile`` and ``run`` target.
This allows for a rapid re-running of a simulator if none of the :term:`RTL` source files have changed and therefore the simulator does not need to recompile the :term:`RTL`.


Variables
=========

The following sections document environment variables and makefile variables according to their owner/consumer.

Of the environment variables, only :envvar:`MODULE` is mandatory to be set
(typically done in a makefile or run script), all others are optional.

..
  If you edit the following sections, please also update the "helpmsg" text in src/cocotb/config.py

Cocotb
------

.. envvar:: TOPLEVEL

    Use this to indicate the instance in the hierarchy to use as the :term:`DUT`.
    If this isn't defined then the first root instance is used.
    Leading and trailing whitespace are automatically discarded.

    The DUT is available in cocotb tests as a Python object at :data:`cocotb.top`;
    and is also passed to all cocotb tests as the :ref:`first and only parameter <quickstart_creating_a_test>`.

    .. versionchanged:: 1.6.0 Strip leading and trailing whitespace

.. envvar:: RANDOM_SEED

    Seed the Python random module to recreate a previous test stimulus.
    At the beginning of every test a message is displayed with the seed used for that execution:

    .. code-block:: bash

        INFO     cocotb.gpi                                  __init__.py:89   in _initialise_testbench           Seeding Python random module with 1377424946


    To recreate the same stimuli use the following:

    .. code-block:: bash

       make RANDOM_SEED=1377424946

    See also: :make:var:`PLUSARGS`

.. envvar:: COCOTB_ANSI_OUTPUT

    Use this to override the default behavior of annotating cocotb output with
    ANSI color codes if the output is a terminal (``isatty()``).

    ``COCOTB_ANSI_OUTPUT=1``
       forces output to be ANSI-colored regardless of the type of ``stdout`` or the presence of :envvar:`NO_COLOR`
    ``COCOTB_ANSI_OUTPUT=0``
       suppresses the ANSI color output in the log messages

.. envvar:: NO_COLOR

    From http://no-color.org,

        All command-line software which outputs text with ANSI color added should check for the presence
        of a ``NO_COLOR`` environment variable that, when present (regardless of its value), prevents the addition of ANSI color.

.. envvar:: COCOTB_REDUCED_LOG_FMT

    Defaults internally to ``1``.
    If the value is ``1``, log lines displayed in the terminal will be shorter.
    It will print only time, message type (``INFO``, ``WARNING``, ``ERROR``, ...) and the log message itself.
    Set to ``0`` if you wish to have the full format message.

.. envvar:: COCOTB_ATTACH

    In order to give yourself time to attach a debugger to the simulator process before it starts to run,
    you can set the environment variable :envvar:`COCOTB_ATTACH` to a pause time value in seconds.
    If set, cocotb will print the process ID (PID) to attach to and wait the specified time before
    actually letting the simulator run.

.. envvar:: COCOTB_ENABLE_PROFILING

    Enable performance analysis of the Python portion of cocotb. When set, a file :file:`test_profile.pstat`
    will be written which contains statistics about the cumulative time spent in the functions.

    From this, a callgraph diagram can be generated with `gprof2dot <https://github.com/jrfonseca/gprof2dot>`_ and ``graphviz``.

.. envvar:: COCOTB_LOG_LEVEL

    The default logging level to use. This is set to ``INFO`` unless overridden.
    Valid values are ``TRACE``, ``DEBUG``, ``INFO``, ``WARNING``, ``ERROR``, ``CRITICAL``.

    ``TRACE`` is used for internal low-level logging and produces very verbose logs.

.. envvar:: COCOTB_RESOLVE_X

    Defines how to resolve bits with a value of ``X``, ``Z``, ``U`` or ``W`` when being converted to integer.
    Valid settings are:

    ``VALUE_ERROR``
       raise a :exc:`ValueError` exception
    ``ZEROS``
       resolve to ``0``
    ``ONES``
       resolve to ``1``
    ``RANDOM``
       randomly resolve to a ``0`` or a ``1``

    Set to ``VALUE_ERROR`` by default.

.. envvar:: LIBPYTHON_LOC

    The absolute path to the Python library associated with the current Python installation;
    i.e. ``libpython.so`` or ``python.dll`` on Windows.
    This is determined with ``cocotb-config --libpython`` in cocotb's makefiles.


Regression Manager
~~~~~~~~~~~~~~~~~~

.. envvar:: MODULE

    The name of the Python module(s) to search for test functions -
    if your tests are in a file called ``test_mydesign.py``, ``MODULE`` would be set to ``test_mydesign``.
    Multiple modules can be specified using a comma-separated list.
    All tests will be run from each specified module in order of the module's appearance in this list.

    The is the only environment variable that is **required** for cocotb, all others are optional.

.. envvar:: TESTCASE

    A regex matching names of test function(s) to run.
    If this variable is not defined cocotb discovers and executes all functions decorated with the :class:`cocotb.test` decorator in the supplied :envvar:`MODULE` list.

    Multiple test function regexes can be specified using a comma-separated list.

.. envvar:: COCOTB_RESULTS_FILE

    The file name where xUnit XML tests results are stored. If not provided, the default is :file:`results.xml`.

    .. versionadded:: 1.3

.. envvar:: COVERAGE

    Enable to report Python coverage data. For some simulators, this will also report :term:`HDL` coverage.

    This needs the :mod:`coverage` Python module to be installed.

.. envvar:: COCOTB_PDB_ON_EXCEPTION

   If defined, cocotb will drop into the Python debugger (:mod:`pdb`) if a test fails with an exception.
   See also the :ref:`troubleshooting-attaching-debugger-python` subsection of :ref:`troubleshooting-attaching-debugger`.


Scheduler
~~~~~~~~~

.. envvar:: COCOTB_SCHEDULER_DEBUG

    Enable additional log output of the coroutine scheduler.


GPI
---

.. envvar:: GPI_EXTRA

    A comma-separated list of extra libraries that are dynamically loaded at runtime.
    A function from each of these libraries will be called as an entry point prior to elaboration,
    allowing these libraries to register system functions and callbacks.
    Note that :term:`HDL` objects cannot be accessed at this time.
    An entry point function must be named following a ``:`` separator,
    which follows an existing simulator convention.

    For example:

    * ``GPI_EXTRA=libnameA.so:entryA,libnameB.so:entryB`` will first load ``libnameA.so`` with entry point ``entryA`` , then load ``libnameB.so`` with entry point ``entryB``.

    .. versionchanged:: 1.4.0
        Support for the custom entry point via ``:`` was added.
        Previously ``:`` was used as a separator between libraries instead of ``,``.

    .. versionchanged:: 1.5.0
        Library name must be fully specified.
        This allows using relative or absolute paths in library names,
        and loading from libraries that `aren't` prefixed with "lib".
        Paths `should not` contain commas.

PyGPI
-----

.. warning::

    PyGPI is an experimental feature and subject to change.


.. envvar:: PYGPI_ENTRY_POINT

    The Python module and callable that starts up the Python cosimulation environment.
    This defaults to :data:`cocotb:_initialise_testbench`, which is the cocotb standard entry point.
    User overloads can be used to enter alternative Python frameworks or to hook existing cocotb functionality.
    The variable is formatted as ``path.to.entry.module:entry_point.function``.
    The string before the colon is the Python module to import
    and the string following the colon is the object to call as the entry function.

    The entry function must be a callable matching this form:

    * ``entry_function(argv: List[str]) -> None``

    The entry module must have the following additional functions defined.
    These additional requirements on the entry module may be relaxed over time.

    * ``_sim_event(message: str) -> None``
    * ``_log_from_c(logger_name: str, level: int, filename: str, lineno: int, msg: str, function_name: str)) -> None``
    * ``_filter_from_c(logger_name: str, level: int) -> bool``

    .. versionchanged:: 1.8
        ``level`` argument to ``_sim_event`` is no longer passed, it is assumed to be `SIM_FAIL` (2).


Makefile-based Test Scripts
---------------------------

The following variables are makefile variables, not environment variables.

.. make:var:: GUI

      Set this to 1 to enable the GUI mode in the simulator (if supported).

.. make:var:: SIM

      Selects which simulator Makefile to use.  Attempts to include a simulator specific makefile from :file:`src/cocotb/share/makefiles/simulators/makefile.$(SIM)`

.. make:var:: WAVES

      Set this to 1 to enable wave traces dump for the Aldec Riviera-PRO, Mentor Graphics Questa, and Icarus Verilog simulators.
      To get wave traces in Verilator see :ref:`sim-verilator-waveforms`.

.. make:var:: TOPLEVEL_LANG

    Used to inform the makefile scripts which :term:`HDL` language the top-level design element is written in.
    Currently it supports the values ``verilog`` for Verilog or SystemVerilog tops, and ``vhdl`` for VHDL tops.
    This is used by simulators that support more than one interface (:term:`VPI`, :term:`VHPI`, or :term:`FLI`) to select the appropriate interface to start cocotb.

    The variable is also made available to cocotb tests conveniently as :data:`cocotb.LANGUAGE`.

.. make:var:: VHDL_GPI_INTERFACE

    Explicitly sets the simulator interface to use when :make:var:`TOPLEVEL_LANG` is ``vhdl``.
    This includes the initial GPI interface loaded, and :make:var:`GPI_EXTRA` library loaded in mixed language simulations.
    Valid values are ``vpi``, ``vhpi``, or ``fli``.
    Not all simulators support all values; refer to the :ref:`simulator-support` section for details.

    Setting this variable is rarely needed as cocotb chooses a suitable default value depending on the simulator used.

.. make:var:: VERILOG_SOURCES

      A list of the Verilog source files to include.
      Paths can be absolute or relative; if relative, they are interpreted as relative to the location where ``make`` was invoked.

.. make:var:: VERILOG_INCLUDE_DIRS

      A list of the Verilog directories to search for include files.
      Paths can be absolute or relative; if relative, they are interpreted as relative to the location where ``make`` was invoked.

.. make:var:: VHDL_SOURCES

      A list of the VHDL source files to include.
      Paths can be absolute or relative; if relative, they are interpreted as relative to the location where ``make`` was invoked.

.. make:var:: VHDL_SOURCES_<lib>

      A list of the VHDL source files to include in the VHDL library *lib* (currently for GHDL/ModelSim/Questa/Xcelium/Incisive only).

.. make:var:: VHDL_LIB_ORDER

      A space-separated list defining the order in which VHDL libraries should be compiled (needed for ModelSim/Questa/Xcelium/Incisive, GHDL determines the order automatically).

.. make:var:: COMPILE_ARGS

      Any arguments or flags to pass to the compile (analysis) stage of the simulation.

.. make:var:: SIM_ARGS

      Any arguments or flags to pass to the execution of the compiled simulation.

.. make:var:: RUN_ARGS

      Any argument to be passed to the "first" invocation of a simulator that runs via a TCL script.
      One motivating usage is to pass `-noautoldlibpath` to Questa to prevent it from loading the out-of-date libraries it ships with.
      Used by Aldec Riviera-PRO and Mentor Graphics Questa simulator.

.. make:var:: EXTRA_ARGS

      Passed to both the compile and execute phases of simulators with two rules, or passed to the single compile and run command for simulators which don't have a distinct compilation stage.

.. make:var:: PLUSARGS

      "Plusargs" are options that are starting with a plus (``+``) sign.
      They are passed to the simulator and are also available within cocotb as :data:`cocotb.plusargs`.
      In the simulator, they can be read by the Verilog/SystemVerilog system functions
      ``$test$plusargs`` and ``$value$plusargs``.

      The special plusargs ``+ntb_random_seed`` and ``+seed``, if present, are evaluated
      to set the random seed value if :envvar:`RANDOM_SEED` is not set.
      If both ``+ntb_random_seed`` and ``+seed`` are set, ``+ntb_random_seed`` is used.

.. make:var:: SIM_CMD_PREFIX

      Prefix for simulation command invocations.

      This can be used to add environment variables or other commands before the invocations of simulation commands.
      For example, ``SIM_CMD_PREFIX := LD_PRELOAD="foo.so bar.so"`` can be used to force a particular library to load.
      Or, ``SIM_CMD_PREFIX := gdb --args`` to run the simulation with the GDB debugger.

      .. versionadded:: 1.6.0

.. make:var:: COCOTB_HDL_TIMEUNIT

      The default time unit that should be assumed for simulation when not specified by modules in the design.
      If this isn't specified then it is assumed to be ``1ns``.
      Allowed values are 1, 10, and 100.
      Allowed units are ``s``, ``ms``, ``us``, ``ns``, ``ps``, ``fs``.

      .. versionadded:: 1.3

.. make:var:: COCOTB_HDL_TIMEPRECISION

      The default time precision that should be assumed for simulation when not specified by modules in the design.
      If this isn't specified then it is assumed to be ``1ps``.
      Allowed values are 1, 10, and 100.
      Allowed units are ``s``, ``ms``, ``us``, ``ns``, ``ps``, ``fs``.

      .. versionadded:: 1.3

.. make:var:: CUSTOM_COMPILE_DEPS

      Use to add additional dependencies to the compilation target; useful for defining additional rules to run pre-compilation or if the compilation phase depends on files other than the :term:`RTL` sources listed in :make:var:`VERILOG_SOURCES` or :make:var:`VHDL_SOURCES`.

.. make:var:: CUSTOM_SIM_DEPS

      Use to add additional dependencies to the simulation target.

.. make:var:: SIM_BUILD

      Use to define a scratch directory for use by the simulator. The path is relative to the location where ``make`` was invoked.
      If not provided, the default scratch directory is :file:`sim_build`.

.. make:var:: SIM_OUTPUT_REDIRECT

      Used to specify how to redirect simulator output.
      Setting to the empty string will prevent redirection.
      Defaults to sending both stdout and stderr to :file:`sim.log` under :make:var:`SIM_BUILD`.

      .. versionadded:: 2.0

.. envvar:: SCRIPT_FILE

    The name of a simulator script that is run as part of the simulation, e.g. for setting up wave traces.
    You can usually write out such a file from the simulator's GUI.
    This is currently supported for the Mentor Questa, Mentor ModelSim and Aldec Riviera simulators.

.. make:var:: TOPLEVEL_LIBRARY

    The name of the library that contains the :make:var:`TOPLEVEL` module/entity.
    Defaults to the :make:var:`RTL_LIBRARY`.
    Only supported by the Siemens EDA Questa simulator.

.. make:var:: RTL_LIBRARY

    The name of the library that contains :make:var:`VHDL_SOURCES` and :make:var:`VERILOG_SOURCES`.
    Only supported by the Aldec Riviera-PRO, Aldec Active-HDL, and Siemens EDA Questa simulators.


Library Build Process
---------------------

You can pass additional options to the library build process
(which is usually happening as part of the installation with ``pip``) using the
`conventional variables <https://www.gnu.org/software/make/manual/html_node/Catalogue-of-Rules.html>`_
for C and C++ compilation and linking:
`CFLAGS`,
`CPPFLAGS`,
and
`LDFLAGS`.

..
   `CXXFLAGS`, `LDLIBS` are not supported by distutils/pip


Internal Variables
------------------

The following variables are used for cocotb internals.
They may change at any time, and users should not rely on them.

.. envvar:: COCOTB_PY_DIR

    Path to the directory containing the cocotb Python package in the :file:`cocotb` subdirectory.

.. envvar:: COCOTB_SHARE_DIR

    Path to the directory containing the cocotb Makefiles and simulator libraries in the subdirectories
    :file:`lib`, :file:`include`, and :file:`makefiles`.

.. envvar:: COCOTB_LIBRARY_COVERAGE

   Enable code coverage collection for cocotb internals.
   When set, a file :file:`.coverage.cocotb` will be written which contains statistics about the code coverage.
   This is mainly useful for cocotb's own Continuous Integration setup.

..
   TODO

   Build Defines
   -------------

   SINGLETON_HANDLES
   PYTHON_SO_LIB

   simulator sim defines