Internal design
===============

Design decisions
----------------

-  Use C++ with additional C API

-  Use exceptions

   -  Use macro wrapper over ``try-catch`` blocks when exceptions off
      (use ``abort()`` if ``THROW()``)

-  Initializes and allocates in the constructor (might throw)

   -  easier code with exceptions ON, with exceptions OFF alloc/init
      failures are not treated as runtime error (program aborts)
   -  break down long initialization in constructor into more private
      methods

-  Implements different devices using inheritance from
   ``GenericModule``, which is the most general implementation of a
   common modem

   -  Internally uses templates with device specialization (modeled as
      ``DCE<SpecificModule>``) which could be used as well for some
      special cases, such as implantation of a minimal device
      (ModuleIf), add new AT commands (oOnly in compile time), or using
      the Module with DTE only (no DCE, no Netif) for sending AT
      commands without network

DCE collaboration model
-----------------------

The diagram describes how the DCE class collaborates with DTE, PPP and
the device abstraction

.. figure:: DCE_DTE_collaboration.png
   :alt: DCE_architecture

   DCE_architecture

Terminal inheritance
--------------------

Terminal is a class which can read or write data, and can handle
callbacks when data are available. UART specialization is provided
implementing these method using the uart driver.

CMUX terminal
-------------

The below diagram depicts the idea of using CMUX terminal mode using the
CMuxInstance class which is a terminal (it implements the basic
read/write methods) interfacing arbitrary number of virtual terminals,
but at the same time it is also composed of CMux class, which consumes
the original terminal and uses its read/write methods to multiplex the
terminal.

.. figure:: CMux_collaboration.png
   :alt: CMUX Terminal

   CMUX Terminal
