Incorrect Bytes being written on OSX

[emgardner]

I am using tokio-serial in a project and I've found that on OSX i am getting incorrect bytes written out over the serial port i've yet to tracedown the cause of the issue exactly. I've confirmed that the same code run's completely fine on Linux/Windows and is only effecting the program on osx.

example code:

use std::time::Duration;

use anyhow::Result;
use tokio::io::{self, AsyncBufReadExt, AsyncReadExt, AsyncWriteExt, BufReader};
use tokio_serial::{self, SerialPort, SerialPortBuilderExt};

#[tokio::main]
async fn main() -> Result<()> {
    let mut port = tokio_serial::new("/dev/ttyUSB0", 38400).open_native_async()?;
    let _ = port.set_exclusive(true);
    let _ = port.set_parity(tokio_serial::Parity::None);
    let _ = port.set_baud_rate(38400);
    let _ = port.set_data_bits(tokio_serial::DataBits::Eight);
    let _ = port.set_stop_bits(tokio_serial::StopBits::One);
    let _ = port.set_flow_control(tokio_serial::FlowControl::None);
    let written = port.write(&[3, 2, 14, 0]).await?;
    let mut buffer: [u8; 5] = [0; 5];
    tokio::time::sleep(Duration::from_millis(10)).await;
    let read = port.read(&mut buffer).await?;
    println!("{buffer:?}");
    Ok(())
}

I explicitly set all of the parameters just in case there was an issue related to that but there was no change.

[package]
name = "client-testing"
version = "0.1.0"
edition = "2024"

[dependencies]
anyhow = "1.0.98"
tokio = { version = "1.45.0", features = ["full"] }
tokio-serial = { version = "5.4.1", features = ["bytes", "codec", "rt"] }

[emgardner]

These are the setting when running with pyserial which works fine.

These are the settings when running with tokio-serial

[emgardner]

This is obviously hacky but manipulating termios to match the python settings makes it work:

use anyhow::Result;
use std::time::Duration;
use tokio::io::{AsyncReadExt, AsyncWriteExt};
use tokio_serial::{DataBits, FlowControl, Parity, SerialPort, SerialPortBuilderExt, StopBits};

use nix::sys::termios::{self, InputFlags, SetArg, SpecialCharacterIndices};
use std::os::unix::io::{AsRawFd, BorrowedFd};

#[tokio::main]
async fn main() -> Result<()> {
   ...
    {
        let raw_fd = port.as_raw_fd();
        let borrowed: BorrowedFd<'_> = unsafe { BorrowedFd::borrow_raw(raw_fd) };
        let mut tio = termios::tcgetattr(&borrowed)?;
        tio.input_flags &= !(InputFlags::IGNBRK | InputFlags::IGNPAR);
        tio.control_chars[SpecialCharacterIndices::VMIN as usize] = 0;
        tio.control_chars[SpecialCharacterIndices::VTIME as usize] = 0;
        termios::tcsetattr(&borrowed, SetArg::TCSANOW, &tio)?;
    }
}

[emgardner]

Actually there seems to be something else going on here as well as just running the following yields the correct result:

    {
        let raw_fd = port.as_raw_fd();
        let borrowed: BorrowedFd<'_> = unsafe { BorrowedFd::borrow_raw(raw_fd) };
        let mut tio = termios::tcgetattr(&borrowed)?;
        termios::tcsetattr(&borrowed, SetArg::TCSANOW, &tio)?;
    }

Which is just rewriting the existing settings so this looks like an initialization error in the underlying serialport-rs