提高DTR线路时出现Windows错误87 (串行)

Question

我正在尝试通过TTL->RS-232转换器与串行设备通信。此转换器要求在DTR和RTS线路上提供电源。

// imports
extern crate serial; //see: https://dcuddeback.github.io/serial-rs/serial/index.html
use std::env;
use std::io;
use std::time::Duration;
use std::process::exit;
use std::io::prelude::*;
use serial::prelude::*;
use serial::{BaudRate, CharSize, Parity, StopBits, FlowControl, SystemPort, PortSettings, Error};
use std::mem;

#[inline]
fn display_error_message(err: &Error, msg: &str) -> ! {
    println!("{}", msg);
    println!("Error Code: {:?}", err.raw_os_error());
    println!("Error:  {:?}", err);
    exit(0);
}

fn main() {
    // open port
    let mut port = match serial::open("COM3") {
        Err(ref e) => display_error_message(e, "Error opening serial port"),
        Ok(x) => x,
    };
    // push settings to stack
    let settings = PortSettings {
        baud_rate: BaudRate::Baud115200,
        char_size: CharSize::Bits8,
        parity: Parity::ParityNone,
        stop_bits: StopBits::Stop1,
        flow_control: FlowControl::FlowNone,
    };
    // configure port
    match port.configure(&settings) {
        Ok(_) => {}
        Err(ref e) => display_error_message(e, "Error configuring serial port."),
    };
    // set rts
    match port.set_rts(true) {
        Ok(_) => {}
        Err(ref e) => display_error_message(e, "Error setting RTS line"),
    };
    // set DTR
    match port.set_dtr(true) {
        Ok(_) => {}
        Err(ref e) => display_error_message(e, "Error setting DTR line"),
    };
    // allocate readbuffer on stack
    let mut rb: [u8; 1] = [0u8; 1];
    // allocate buffer to hold output
    let mut out: String = String::with_capacity(1024);
    // loop while reading
    loop {
        match port.read(&mut rb) {
            Ok(_) => {}
            Err(ref e) => {
                println!("Error reading serial port.");
                println!("Error:  {:?}", e);
                exit(0);
            }
        };
        match rb[0] {
            // Linefeed
            10 => {
                println!("{}<LF>", &out);
                out = String::with_capacity(1024);
            }
            // carriage return
            13 => {
                println!("{}<CR>", &out);
                out = String::with_capacity(1024);
            }
            // normal chars
            32...126 => {
                let temp: u32 = rb[0].clone() as u32;
                let ch: char = unsafe { mem::transmute(temp) };
                out.push(ch);
            }
            // everything else
            x => {
                println!("Non standard character encountered");
                println!("Value:  {:?}", x);
                exit(0);
            }
        };
    }
}

源代码也在Rust Playground和Github上。

我使用的是serial-rs库和Rust 1.8 (GNU ABI Windows7 x64专业版)。

我的错误发生在第46行：

 match port.set_dtr( true ) {
     Ok(_) => { },
     Err(ref e) => display_error_message(e,"Error setting DTR line")
 };

这将返回错误代码87 (在Windows 7上)。标准serial-rs不保存错误代码，所以我使用my own fork (等待PR)。

此错误来自格式错误的系统调用。深入serial-rs，你会发现set_dtr(bool)只是包装了一个对EscapeCommFunction(2) first call，second call，third call的调用。参数代码显示为correct。

使用MSVC工具链进行编译会导致相同的错误，将DTR调用放在RTS调用之前会导致相同的错误。

同时提升DTR和RTS在py-serial中工作，但我不能在这样做的同时写入端口。See other issue

Answer 1

USB->RS232转换器的串行端口仿真驱动程序不支持DTR线路导致的错误。