How do I reset a USB device using a script?

Question

I have a USB GSM modem that does not always work property (Huawei E367u-2) Sometimes it gets reset (USB device disconnect/reconnect in logs) and when it comes back up, it has different ttyUSB numbers. Sometimes on boot, usb_modeswitch seems to just not get fired. The computer is a Raspberry Pi running Raspbian.

I have a simple solution to this: every minute cron runs the following script (pseudo-code):

If WVDIAL is not running:
    Run WVDIAL

I want to change the script to be this:

If /dev/ttyUSB0 is not present:
    If DevicePresent(12d1:1446):
        ResetDevice(12d1:1446)
    ElseIf DevicePresent(12d1:1506)
        ResetUSB(12d1:1506)
If WVDIAL is not running:
    Run WVDIAL

Obviously this is pseudo-code, but I have the following lines that I need to string together but I can't figure out how:

This loads wvdial if it is not running:

#! /bin/sh 
# /etc/init.d/wvdial

### BEGIN INIT INFO
# Provides:          TheInternet
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Simple script to start a program at boot
# Description:       A simple script from www.stuffaboutcode.com which will start / stop a program a boot / shutdown.
### END INIT INFO

# If you want a command to always run, put it here

# Carry out specific functions when asked to by the system
case "$1" in
  start)
    echo "Starting GPRS Internet"
    # run application you want to start
    /sbin/start-stop-daemon --start --background --quiet --exec /usr/bin/wvdial internet
    ;;
  stop)
    echo "Stopping GPRS Internet"
    # kill application you want to stop
    /sbin/start-stop-daemon --stop --exec /usr/bin/wvdial 
    ;;
  *)
    echo "Usage: /etc/init.d/noip {start|stop}"
    exit 1
    ;;
esac

exit 0

This lets me find the /sys path to a certain device:

for X in /sys/bus/usb/devices/*; do
    echo "$X"
    cat "$X/idVendor" 2>/dev/null
    cat "$X/idProduct" 2>/dev/null
    echo
done

And this resets a USB device if you know the correct /sys path:

echo 0 > /sys/bus/usb/devices/1-1.2.1.1/authorized
echo 1 > /sys/bus/usb/devices/1-1.2.1.1/authorized

So, I need to string together those last 2 sections and a test to /dev/ttyUSB0 into a section that goes under the "If you want a command to always run, put it here" comment.

• How can I do that?
• Is there a better way to do this?

Answer 1

I think you're basically there:

#!/bin/sh

for X in /sys/bus/usb/devices/*
do
    if [ -e "$X/idVendor" ] && [ -e "$X/idProduct" ] \
           && [ 12d1 = $(cat "$X/idVendor") ] && [ 1446 = $(cat "$X/idProduct") ]
    then
        echo 0 >"$X/authorized"
        # might need a small sleep here
        echo 1 >"$X/authorized"
    fi
done

This loops over all devices (as you were doing) and each time it finds a match for the vendor:product ids, it applies the reset which works for you.

---

As an aside, you might want to look into the watchdog program as an alternative to your cron job.

Answer 2

If you are thinking to use a command line and then reset it.

Save the following as usbreset.c

/* usbreset -- send a USB port reset to a USB device */

#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>

#include <linux/usbdevice_fs.h>


int main(int argc, char **argv)
{
    const char *filename;
    int fd;
    int rc;

    if (argc != 2) {
        fprintf(stderr, "Usage: usbreset device-filename\n");
        return 1;
    }
    filename = argv[1];

    fd = open(filename, O_WRONLY);
    if (fd < 0) {
        perror("Error opening output file");
        return 1;
    }

    printf("Resetting USB device %s\n", filename);
    rc = ioctl(fd, USBDEVFS_RESET, 0);
    if (rc < 0) {
        perror("Error in ioctl");
        return 1;
    }
    printf("Reset successful\n");

    close(fd);
    return 0;
}

The run the following commands in terminal:

Compile the program:

$ cc usbreset.c -o usbreset Get the Bus and Device ID of the USB device you want to reset:

$ lsusb
Bus 002 Device 003: ID 0fe9:9010 DVICO
Make our compiled program executable:

$ chmod +x usbreset Execute the program with sudo privilege; make necessary substitution for <Bus> and <Device> ids as found by running the lsusb command:

$ sudo ./usbreset /dev/bus/usb/002/003

Else

#!/usr/bin/env python
import os
import sys
from subprocess import Popen, PIPE
import fcntl
driver = sys.argv[-1]
print "resetting driver:", driver
USBDEVFS_RESET= 21780

try:
    lsusb_out = Popen("lsusb | grep -i %s"%driver, shell=True, bufsize=64, stdin=PIPE, stdout=PIPE, close_fds=True).stdout.read().strip().split()
    bus = lsusb_out[1]
    device = lsusb_out[3][:-1]
    f = open("/dev/bus/usb/%s/%s"%(bus, device), 'w', os.O_WRONLY)
    fcntl.ioctl(f, USBDEVFS_RESET, 0)
except Exception, msg:
    print "failed to reset device:", msg

In my case it was the cp210x driver (which I could tell from lsmod | grep usbserial), so you could save the above snippet as reset_usb.py and then do this:

sudo python reset_usb.py cp210x

This might also be helpful if you don't already have a c compiler setup on your system, but you do have python.

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