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133 lines
4.0 KiB
ReStructuredText
133 lines
4.0 KiB
ReStructuredText
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ESP MODEM
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=========
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This component is used to communicate with modems in the command mode
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(using AT commands), as well as the data mode (over PPPoS protocol). The
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modem device is modeled with a DCE (Data Communication Equipment)
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object, which is composed of:
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- DTE (Data Terminal Equipment), which abstracts the terminal (currently only UART implemented).
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- PPP Netif representing a network interface communicating with the DTE using PPP protocol.
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- Module abstracting the specific device model and its commands.
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::
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+-----+
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| DTE |--+
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+-----+ | +-------+
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+-->| DCE |
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+-------+ | |o--- set_mode(command/data)
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| Module|--->| |
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+-------+ | |o--- send_commands
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+->| |
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+------+ | +-------+
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| PPP |--+
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| netif|------------------> network events
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+------+
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Modem components
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----------------
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DCE
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~~~
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This is the basic operational unit of the esp_modem component,
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abstracting a specific module in software, which is basically configured
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by
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- the I/O communication media (UART), defined by the DTE configuration
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- the specific command library supported by the device model, defined with the module type
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- network interface configuration (PPPoS config in lwip)
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After the object is created, the application interaction with the DCE is
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in
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- issuing specific commands to the modem
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- switching between data and command mode
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DTE
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~~~
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Is an abstraction of the physical interface connected to the modem.
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Current implementation supports only UART
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PPP netif
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~~~~~~~~~
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Is used to attach the specific network interface to a network
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communication protocol used by the modem. Currently implementation
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supports only PPPoS protocol.
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Module
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~~~~~~
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Abstraction of the specific modem device. Currently the component
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supports SIM800, BG96, SIM7600.
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Use cases
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---------
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Users interact with the esp-modem using the DCE’s interface, to
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basically
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- Switch between command and data mode to connect to the internet via cellular network.
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- Send various commands to the device (e.g. send SMS)
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The applications typically register handlers for network events to
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receive notification on the network availability and IP address changes.
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Common use cases of the esp-modem are also listed as the examples:
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- ``examples/pppos_client`` – simple client which reads some module properties and switches to the data mode to connect to a public mqtt broker.
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- ``examples/modem_console`` – is an example to exercise all possible module commands in a console application.
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- ``examples/ap_to_pppos`` – this example focuses on the network
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connectivity of the esp-modem and provides a WiFi AP that forwards
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packets (and uses NAT) to and from the PPPoS connection.
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Extensibility
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-------------
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CMUX
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~~~~
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Implementation of virtual terminals is an experimental feature, which
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allows users to also issue commands in the data mode, after creating
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multiple virtual terminals, designating some of them solely to data
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mode, others solely to command mode.
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DTE’s
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~~~~~
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Currently, we support only UART (and USB as a preview feature), but
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modern modules support other communication interfaces, such as USB, SPI.
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Other devices
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~~~~~~~~~~~~~
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Adding a new device is a must-have requirement for the esp-modem
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component. Different modules support different commands, or some
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commands might have a different implementation. Adding a new device
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means to provide a new implementation as a class derived from
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``GenericModule``, where we could add new commands or modify the
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existing ones.
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Configuration
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-------------
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Modem abstraction is configurable both compile-time and run-time.
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Component Kconfig
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~~~~~~~~~~~~~~~~~
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Compile-time configuration is provided using menuconfig. Please check
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the description for the CMUX mode configuration options.
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Runtime configuration
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~~~~~~~~~~~~~~~~~~~~~
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Is defined using standard configuration structures for ``DTE`` and
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``DCE`` objects separately. Please find documentation of
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- :cpp:class:``esp_modem_dte_config_t``
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- :cpp:class:``esp_modem_dce_config_t``
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