Serial Core

The serial-core crate provides abstract types used to interface with and implement serial ports. They can be used to write code that functions generically over all serial port types and to implement new serial port types that work with generic code.

• Documentation

Usage

Add serial-core as a dependency in Cargo.toml:

[dependencies]
serial-core = "0.4"

Interfacing with an Open Serial Port

Import the serial-core crate and everything from the serial_core::prelude module. The traits in the serial_core::prelude module are useful to have in scope to resolve trait methods when working with serial ports, and they are unlikely to conflict with other crates.

extern crate serial_core as serial;

use std::io;
use std::time::Duration;

use std::io::prelude::*;
use serial::prelude::*;

Configuration and I/O

Interfacing with a serial port is done through the SerialPort, std::io::Read, and std::io::Write traits, which provide methods for configuration, I/O, and control signals.

fn probe<P: SerialPort>(port: &mut P) -> io::Result<()> {
    let mut buf: Vec<u8> = (0..255).collect();

    // configuration
    try!(port.reconfigure(&|settings| {
        try!(settings.set_baud_rate(serial::Baud9600));
        settings.set_char_size(serial::Bits8);
        settings.set_parity(serial::ParityNone);
        settings.set_stop_bits(serial::Stop1);
        settings.set_flow_control(serial::FlowNone);
        Ok(())
    }));

    // I/O
    try!(port.set_timeout(Duration::from_millis(100)));
    try!(port.write(&buf[..]));
    try!(port.read(&mut buf[..]));

    // control signals
    try!(port.set_dtr(true));
    try!(port.read_dsr());

    Ok(())
}

For details on using an open serial port, refer to the documentation for the SerialPort trait.

Taking Ownership of a Serial Port

Often times, you'll want to implement a higher-level protocol over a serial port, in which case you'll probably want a handle object that owns the serial port and provides an interface specific to the higher-level protocol.

To implement a handle for generic serial ports without requiring a proliferation of generics, one can define the higher-level protocol in a trait:

struct Handle<P: SerialPort> {
    port: P,
}

impl<P: SerialPort> Handle<P> {
    fn new(port: P) -> Self {
        Handle { port: port }
    }
}

impl<P: SerialPort> Greet for Handle<P> {
    fn get_name(&mut self) -> serial::Result<String> {
        let mut name = String::new();

        try!(self.port.write("What is your name? "));
        try!(self.port.read_to_string(&mut name));

        Ok(name)
    }

    fn say_hello(&mut self, name: &String) -> serial::Result<()> {
        try!(writeln!(&mut self.port, "Hello, {}!", name));
        Ok(())
    }
}

fn greet(greeter: &mut Greet) -> serial::Result<()> {
    let name = try!(greeter.get_name());

    greeter.say_hello(name)
}

Note that in the above example, the greet() function can interact with the Handle struct via the Greet trait without caring what type of SerialPort it's talking to.

Alternatively, since SerialPort is object-safe, it can be boxed inside of the handle. However, this approach may introduce an extra pointer indirection:

struct Handle {
    port: Box<SerialPort>,
}

impl Handle {
    fn new<P: SerialPort>(port: P) -> Self {
        Handle { port: Box::new(port) }
    }

    fn get_name(&mut self) -> serial::Result<String> {
        // ...
    }

    fn say_hello(&mut self, name: &String) -> serial::Result<()> {
        // ...
    }
}

Implementing a Custom Serial Port

The serial port crates are designed to be extensible, allowing third parties to define custom serial port types. Reasons for implementing a custom serial port type may include bridging a serial port to a TCP socket or other I/O device, providing a fake implementation for testing, or integrating with custom hardware.

To define a custom serial port type, start by importing the serial_core crate:

extern crate serial_core as serial;

use std::io;
use std::time::Duration;

Next, define a type that will implement the new serial port and optionally a type for its settings:

struct CustomSerialPort {
    // ...
}

struct CustomSerialPortSettings {
    // ...
}

Implement SerialDevice, std::io::Read, and std::io::Write for the new serial port type:

impl serial::SerialDevice for CustomSerialPort {
    type Settings = CustomSerialPortSettings;

    fn read_settings(&self) -> serial::Result<Self::Settings> { ... }
    fn write_settings(&mut self, settings: &Self::Settings) -> serial::Result<()> { ... }
    fn timeout(&self) -> Duration { ... }
    fn set_timeout(&mut self, timeout: Duration) -> serial::Result<()> { ... }

    fn set_rts(&mut self, level: bool) -> serial::Result<()> { ... }
    fn set_dtr(&mut self, level: bool) -> serial::Result<()> { ... }
    fn read_cts(&mut self) -> serial::Result<bool> { ... }
    fn read_dsr(&mut self) -> serial::Result<bool> { ... }
    fn read_ri(&mut self) -> serial::Result<bool> { ... }
    fn read_cd(&mut self) -> serial::Result<bool> { ... }
}

impl io::Read for CustomSerialPort {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> { ... }
}

impl io::Write for CustomSerialPort {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> { ... }
    fn flush(&mut self) -> io::Result<()> { ... }
}

If a custom settings type is not needed, then the PortSettings struct can be used for the SerialDevice::Settings associated type. Otherwise, the Settings type must implement SerialPortSettings:

impl serial::SerialPortSettings for CustomSerialPortSettings {
    fn baud_rate(&self) -> Option<BaudRate> { ... }
    fn char_size(&self) -> Option<CharSize> { ... }
    fn parity(&self) -> Option<Parity> { ... }
    fn stop_bits(&self) -> Option<StopBits> { ... }
    fn flow_control(&self) -> Option<FlowControl> { ... }

    fn set_baud_rate(&mut self, baud_rate: BaudRate) -> serial::Result<()> { ... }
    fn set_char_size(&mut self, char_size: CharSize) { ... }
    fn set_parity(&mut self, parity: Parity) { ... }
    fn set_stop_bits(&mut self, stop_bits: StopBits) { ... }
    fn set_flow_control(&mut self, flow_control: FlowControl) { ... }
}

For details on implementing a new serial port type, refer to the documentation for the SerialDevice trait.

License

Copyright © 2015 David Cuddeback

Distributed under the MIT License.