IO in Erlang
============

How a Driver Looks Like
-----------------------

A port driver is a C module with several functions defined (see ``ErlDrvEntry``
in ``emulator/beam/erl_driver.h``:

*   Start/stop, finish, process exit/emergency close functions
*   IO events (async/input/output)
*   Timeout handler
*   Call function, which passes commands to the port
*   Control function, which changes options in the port
*   Flush function, which ensures that all data is written

Making a Port Driver
--------------------

Define an ``erl_drv_entry`` variable (a struct) and fill it with pointers to
callback functions.
You will need to cover things such as starting your driver,
stopping it, opening a port, sending commands and receiving data, and few other.

.. seealso::
    BEAM Wisdoms: :doc:`interfacing`

    `Driver HowTo <http://erlang.org/doc/man/erl_driver.html>`_

    `Port Driver and erl_drv_entry documentation <http://erlang.org/doc/man/driver_entry.html>`_

Load your port driver and register it in the system under a name
(``add_driver_entry``).

.. seealso::
    `Erl Dynamic Driver Loader Linker <http://erlang.org/doc/man/erl_ddll.html>`_

.. todo::
    this goes to indepth section