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80 lines
3.3 KiB
Markdown
80 lines
3.3 KiB
Markdown
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# ESP MODEM
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This component is used to communicate with modems in the command mode (using AT commands), as well as the data mode
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(over PPPoS protocol).
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The modem device is modeled with a DCE (Data Communication Equipment) 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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```
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## Modem components
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### DCE
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This is the basic operational unit of the esp_modem component, abstracting a specific module in software,
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which is basically configured 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 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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Is an abstraction of the connected interface. Current implementation supports only UART
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### PPP
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Is used to connect the specific network interface to the modem data mode. Currently implementation supports only PPPoS protocol.
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### Module
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Abstraction of the specific modem device. Currently the component supports SIM800, BG96, SIM7600.
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## Use cases
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Users could interact with the esp-modem using the DCE's interface, to 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 receive notification on the network availability and
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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 modules commands in a console application.
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* `examples/ap_to_pppos` -- this example focuses on the network connectivity of the esp-modem and provides a WiFi AP
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that forwards packets (and uses NAT) to and from the PPPoS connection.
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## Extensibility
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### CMUX
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Implementation of virtual terminals is an experimental feature, which allows users to also issue commands in the data mode,
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after creating multiple virtual terminals, designating some of them solely to the data mode, while other to command mode.
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### DTE's
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Currently we support only UART, but modern modules support other communication interfaces, such as USB, SPI.
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### Other devices
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Adding a new device is a must-have requirement for the esp-component. Different modules support different commands,
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or some commands might have a different implementation. Adding a new device means to provide a new implementation
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as a class derived from `GenericModule`, where we could add new commands or modify the existing ones.
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