linux usb gadget serialport, get Not a typewriter

[cppcoffee]

Open the usb gadget serialport, get an error occurs.

The source code is as follows:

use serialport::{DataBits, Parity, StopBits};
use std::io::Read;
use std::io::{self, Write};
use std::time::Duration;

fn main() {
    let mut port = serialport::new("/dev/ttyGS0", 9600)
        .parity(Parity::None)
        .stop_bits(StopBits::One)
        .data_bits(DataBits::Eight)
        .timeout(Duration::from_secs(120))
        .open_native()
        .unwrap();       // Not a typewriter
...

Error message:

thread 'main' panicked at src/main.rs:13:10:
called `Result::unwrap()` on an `Err` value: Error { kind: Unknown, description: "Not a typewriter" }

[sirhcel]

Sorry to hear that @cppcoffee! Let's dig into what's causing this. How do you set up the USB gadget device in question? Could you run your example with RUST_BACKTRACE set to 1? For example by setting in beforehand like:

$ export RUST_BACKTRACE=1

[asmforce]

It's not the same issue but seems to be related: 4.7.0 fails to work with virtual serial port created by socat utility while 4.6.1 works perfectly fine:

$ cargo build --release
   Compiling proc-macro2 v1.0.93
   Compiling unicode-ident v1.0.14
   Compiling libc v0.2.169
   Compiling pkg-config v0.3.31
   Compiling thiserror v1.0.69
   Compiling bitflags v1.3.2
   Compiling cfg-if v1.0.0
   Compiling bitflags v2.8.0
   Compiling scopeguard v1.2.0
   Compiling libudev-sys v0.1.4
   Compiling quote v1.0.38
   Compiling syn v2.0.96
   Compiling nix v0.26.4
   Compiling libudev v0.3.0
   Compiling thiserror-impl v1.0.69
   Compiling unescaper v0.1.5
   Compiling serialport v4.7.0
   Compiling experiments-rs v1.0.0 (/home/asmforce/work/experiments-rs)
    Finished `release` profile [optimized] target(s) in 2.52s
$ ./target/release/experiments-rs 
Error: Custom { kind: Other, error: "Not a typewriter" }
$ cargo update serialport
    Updating crates.io index
     Locking 1 package to latest compatible version
 Downgrading serialport v4.7.0 -> v4.6.1 (available: v4.7.0)
$ cargo build --release
   Compiling serialport v4.6.1
   Compiling experiments-rs v1.0.0 (/home/asmforce/work/experiments-rs)
    Finished `release` profile [optimized] target(s) in 0.52s
$ ./target/release/experiments-rs 
Written 4 bytes
Success

Here's the app's source code:

use std::io::{Error, Write};
use std::time::Duration;
use serialport::{FlowControl, DataBits, Parity, StopBits};

fn main() -> Result<(), Error> {
    let path = "/dev/ttyTEST";
    let builder = serialport::new(path, 9600)
        .flow_control(FlowControl::None)
        .data_bits(DataBits::Eight)
        .parity(Parity::None)
        .stop_bits(StopBits::One)
        .timeout(Duration::from_millis(1000));

    let mut port = builder.open()?;

    let data = [12u8, 23u8, 34u8, 45u8];
    match port.write(&data) {
        Ok(count) => println!("Written {} bytes", count),
        Err(e) => println!("{}", e)
    }

    match port.flush() {
        Ok(()) => println!("Success"),
        Err(e) => println!("{}", e)
    }

    Ok(())
}

And here is the command to create a virtual serial port:

sudo socat -d -d pty,link=/tmp/cvsimulator_sp,echo=0,perm=0777,b9600 pty,link=/dev/ttyTEST,echo=0,perm=0777,b9600

[sirhcel]

Thank you for bringing up the issue with Linux pseudo terminals @asmforce!

At a first glance, I have no idea how to reliably detect whether the actual device is supposed to support setting control lines. But trying on best-effort looks like a way to go. See sirhcel@9b56161.

[cppcoffee]

Hi @sirhcel , testing revealed issues with serialport version 4.7.0, while version 4.6.1 works normally.

The test code is as follows:

fn test_serial() {
    let mut buf = [0; 4096];

    let mut port = serialport::new("/dev/ttyGS0", 1_500_000)
        .parity(Parity::Even)
        .stop_bits(StopBits::One)
        .data_bits(DataBits::Eight)
        .timeout(Duration::from_secs(120))
        .open_native()
        .unwrap();

    loop {
        let _n = port.read(&mut buf).unwrap();
    }
}