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Updated internal design document

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David Cermak
2021-03-30 08:36:04 +02:00
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esp_modem/docs/internal_desing.md
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## Design decisions ## Design decisions
* Use C++ (lambdas, templates) with additional C API * Use C++ with additional C API
| esp-modem in C | esp-modem in C++ | | esp-modem in C | esp-modem in C++ |
|----------------|---------------| |----------------|---------------|
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-3908 -3908
``` ```
* Use exceptions (implement nothrow? possibly using `assert()`) * Use exceptions
- Use macro wrapper over `try-catch` blocks when exceptions off (use `abort()` if `THROW()`)
| exceptions off | exceptions on | | exceptions off | exceptions on |
|----------------|---------------| |----------------|---------------|
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``` ```
* Initializes and allocates in the constructor (might 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) - easier code with exceptions ON, with exceptions OFF alloc/init failures are not treated as runtime error (program aborts)
* Implements different devices with template specialization - break down long initialization in constructor into more private methods
- Specific device abstraction overrides methods, but does not use virtual function dispatch (modeled as `DCE<SpecificModule>`) * Implements different devices using inheritance from `GenericModule`, which is the most general implementation of a common modem
- Use cases: Implement a minimal device (ModuleIf), add new AT commands (oOnly in compile time). - Internally uses templates with device specialization (modeled as `DCE<SpecificModule>`) which could be used as well for some special cases,
- Possibly use Module with DTE only (no DCE, no Netif) for sending AT commands without network 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
Example:
```
class SIM7600: public GenericModule {
using GenericModule::GenericModule;
public:
command_result get_module_name(std::string& name); // overrides, but is no virtual
};
```
method `get_module_name()` reimplements the *same* method in `GenericModule`
## DCE collaboration model ## DCE collaboration model
The diagram describes how the DCE class collaborates with DTE, PPP and the device abstraction The diagram describes how the DCE class collaborates with DTE, PPP and the device abstraction