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99 lines
1.9 KiB
Markdown
99 lines
1.9 KiB
Markdown
# Creating Portable Drivers
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---
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## These things are different
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* STM32F030 UART Driver
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* nRF52840 UART Driver
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* But I want to write a library which is generic!
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* e.g. an AT Command Parser
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---
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## How does Rust allow generic behaviour?
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* Generics!
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* `where T: SomeTrait`
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---
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## Traits
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```rust
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trait GenericSerial {
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type Error;
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fn read(&mut self, buffer: &mut [u8]) -> Result<usize, Error>;
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fn write(&mut self, buffer: &[u8]) -> Result<usize, Error>;
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}
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```
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---
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## My Library...
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```rust
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struct AtCommandParser<T> {
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uart: T,
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...
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}
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impl<T> AtCommandParser<T> where T: GenericSerial {
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fn new(uart: T) -> AtCommandParser<T> { ... }
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fn get_command(&mut self) -> Result<Option<AtCommand>, Error> { ... }
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}
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```
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Note how `AtCommandParser` *owns* the object which meets the `GenericSerial` trait.
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---
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## My Application
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```rust
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let uart = stm32_hal::Uart::new(...);
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let at_parser = at_library::AtCommandParser::new(uart);
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while let Some(cmd) = at_parser.get_command().unwrap() {
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...
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}
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```
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---
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## My Application (2)
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```rust
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let uart = nrf52_hal::Uart::new(...);
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let at_parser = at_library::AtCommandParser::new(uart);
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while let Some(cmd) = at_parser.get_command().unwrap() {
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...
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}
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```
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---
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## How do we agree on the traits?
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* The Rust Embedded Working Group has developed some traits
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* They are called the *Embedded HAL*
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* See https://docs.rs/embedded-hal/
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* All HAL implementations should implement these traits
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---
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## Blocking vs Non-blocking
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* Should a trait API stall your CPU until the data is ready?
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* Or should it return early, saying "not yet ready"
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* So you can go an do something else in the mean time?
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* Or sleep?
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* `embedded_hal::blocking::serial::Write`, vs
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* `embedded_hal::serial::Write`
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---
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## Trade-offs
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* Some MCUs have more features than others
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* The trait design has an inherent trade-off
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* Flexibility/Performance vs Portability
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