Compiling
=========

Compilation of the GPU-enabled MPAS-Atmosphere code is different from compiling
a standard release of MPAS-Atmosphere in only one respect: The option ``OPENACC=true``
must be added to the compilation command. For example::

    make -j 4 pgi CORE=atmosphere USE_PIO2=true OPENACC=true

Through the specification of ``OPENACC=true`` in the build command, additional
compiler flags will be added. At present, these include ``-Mnofma -acc -ta=tesla:cc70 -Minfo=accel``.

As described in the :ref:`supported platform<Supported platforms>` section, only
the PGI compilers are supported at present; accordingly, the use of ``OPENACC=true``
only adds additional flags for the ``pgi`` build target.

If the model was successfully compiled for execution on GPUs, the build summary
should indicate that OpenACC was enabled:

.. code-block:: text
    :emphasize-lines: 8

    *******************************************************************************
    MPAS was built with default double-precision reals.
    Debugging is off.
    Parallel version is on.
    Papi libraries are off.
    TAU Hooks are off.
    MPAS was built without OpenMP support.
    MPAS was built with OpenACC enabled.
    MPAS was built with .F files.
    The native timer interface is being used
    Using the PIO 2 library.
    *******************************************************************************