.. _controller_channels:

Controller Communication Channels
==================================
Communication between the controller and the host computer shall occur over four
abstract communication channels:

#. :ref:`data-rd-chan`: Read-only, high-bandwidth stream of device output
   :ref:`frames<frame>` from controller to host.
#. :ref:`data-wr-chan`: Write-only, high-bandwidth stream of device input
   :ref:`frames<frame>` from mhost to controller.
#. :ref:`sig-chan`: Read-only stream of short-messages and asynchronous hardware
   events from controller to host.
#. :ref:`conf-chan`: Bidirectional, addressed access to device registers.

These channels are implemented by the combination of the controller hardware and
the :term:`Driver Translator`.

Concurrent access to a single channel by the host (e.g., by multiple threads of
execution or applications) is NOT permitted. However, individual channels MUST
be able to be accessed independently.

.. note:: Concurrent access requirements relate only to the hardware
   implementation. Functions in a high-level :term:`API` MAY introduce their own
   access dependencies and concurrency limitations.

The required characteristics of the controller channels are described in the
following sections.

.. toctree::
   :hidden:

   data_frames
   read_channel
   write_channel
   signal_channel
   configuration_channel