WSL1 ignores CTS/DSR input lines in serial ports

[0wwafa]

Windows Version

Windows 10

WSL Version

WSL version: 2.3.24.0 Kernel version: 5.15.153.1-2 WSLg version: 1.0.65 MSRDC version: 1.2.5620 Direct3D version: 1.611.1-81528511 DXCore version: 10.0.26100.1-240331-1435.ge-release Windows version: 10.0.19045.5073

Are you using WSL 1 or WSL 2?

• WSL 2
• WSL 1

Kernel Version

5.15.153.1-2

Distro Version

Ubuntu 22.04

Other Software

WSL version: 2.3.24.0
Kernel version: 5.15.153.1-2
WSLg version: 1.0.65
MSRDC version: 1.2.5620
Direct3D version: 1.611.1-81528511
DXCore version: 10.0.26100.1-240331-1435.ge-release
Windows version: 10.0.19045.5073

Repro Steps

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <termios.h>

void print_status(int status) {
    printf("Status: ");
    if (status & TIOCM_RNG) printf("RI ");
    if (status & TIOCM_DSR) printf("DSR ");
    if (status & TIOCM_CAR) printf("DCD ");
    if (status & TIOCM_CTS) printf("CTS ");
    if (status & TIOCM_DTR) printf("DTR ");
    if (status & TIOCM_RTS) printf("RTS ");
    if (status & TIOCM_RI) printf("RX ");
    printf("\n");
}

int main(int argc, char *argv[]) {
    if (argc < 2 || argc > 3) {
        fprintf(stderr, "Usage: %s <serial_port> [speed]\n", argv[0]);
        return 1;
    }

    int speed = (argc == 3) ? atoi(argv[2]) : 1000000;

    int fd = open(argv[1], O_RDWR | O_NOCTTY | O_NDELAY);
    if (fd == -1) {
        perror("open");
        return 1;
    }

    struct termios options;
    tcgetattr(fd, &options);
    cfsetispeed(&options, speed);
    cfsetospeed(&options, speed);
    options.c_cflag |= (CLOCAL | CREAD);
    tcsetattr(fd, TCSANOW, &options);

    int prev_status = 0;
    ioctl(fd, TIOCMGET, &prev_status);
    print_status(prev_status);

    while (1) {
        int curr_status;
        ioctl(fd, TIOCMGET, &curr_status);
        if (curr_status != prev_status) {
            print_status(curr_status);
            prev_status = curr_status;
        }
        usleep(100000); // Sleep for 100ms
    }

    close(fd);
    return 0;
}

The above program works on Linux, unix (in general) and if compiled using MSYS2 or CYGWIN it works on windows too.

IN WSL1 CTS (and probably other signals) are ignored and fixed.

Expected Behavior

The same as in linux/windows :D

Actual Behavior

Shorting CTS to ground does not show any change in the program (it does if compiled with MSYS2 or CYGWIN for windows and it does on any other system.

Diagnostic Logs

No need.

[github-actions]

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Invoke-WebRequest -UseBasicParsing "https://raw.githubusercontent.com/microsoft/WSL/master/diagnostics/collect-wsl-logs.ps1" -OutFile collect-wsl-logs.ps1
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.\collect-wsl-logs.ps1

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View similar issues

Please view the issues below to see if they solve your problem, and if the issue describes your problem please consider closing this one and thumbs upping the other issue to help us prioritize it!

Closed similar issues:

• WSL1 Communication With Serial Ports Does Not Work (#10129), similarity score: 0.74
• CH341-based USB-UART adapter in WSL, RX works but TX does not. (#3422), similarity score: 0.71
• COM port device not enumarating in WSL 1 (#5203), similarity score: 0.70

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