esp_modem: Moved to component folder

components/esp_modem/docs/advanced_api.rst

@@ -0,0 +1,48 @@
+Advanced esp-modem use cases
+============================
+
+This chapter outlines basic extensibility of the esp-modem component.
+
+.. _dce_factory:
+
+Custom instantiation with DCE factory
+--------------------------------------
+
+It is possible to create a modem handle in many different ways:
+
+- Build a DCE on top a generic module, user defined module or build the module only (in case the application will only use AT command interface)
+- Create the DCE as a shared, unique or a vanilla pointer
+- Create a generic DCE or a templated DCE_T of a specific module (this could be one of the supported modules or a user defined module)
+
+All the functionality is provided by the DCE factory
+
+.. doxygengroup:: ESP_MODEM_DCE_FACTORY
+   :members:
+
+
+Create custom module
+--------------------
+
+Creating a custom module is necessary if the application needs to use a specific device that is not supported
+and their commands differ from any of the supported devices. In this case it is recommended to define a new class
+representing this specific device and derive from the :cpp:class:`GenericModule`. In order to instantiate
+the appropriate DCE of this module, application could use :ref:`the DCE factory<dce_factory>`, but build the DCE with
+the specific module, using :cpp:func:`esp_modem::dce_factory::Factory::build`.
+
+Please refer to the implementation of the existing modules.
+
+Please note that the ``modem_console`` example defines a trivial custom modem DCE which overrides one command,
+for demonstration purposes only.
+
+
+Create new communication interface
+----------------------------------
+
+In order to connect to a device using an unsupported interface (e.g. SPI or I2C), it is necessary to implement
+a custom DTE object and supply it into :ref:`the DCE factory<dce_factory>`. The DCE is typically created in two steps:
+
+- Define and create the corresponding terminal, which can communicate on the custom interface. This terminal should support basic IO methods defined in :cpp:class:`esp_modem::Terminal` and derive from it.
+- Create the DTE which uses the custom Terminal
+
+Please refer to the implementation of the existing UART DTE.
+