How to restart ttyusb*

Question

I have two devices that are continuously feeding data through ttyUSB0 and ttyUSB1. I have php scripts that are using this data. The problem I am running into is that sometimes the feed just kind of freezes. The best way I've seen to fix this is to unplug the BUB board from the computer and plug it in again. However, I am looking for a way to automate this action. Is there a way to to tell linux to essentially eject the BUB board and then somehow pick it up again?

Answer 1

I'm having the same problem as you but in a different context ( I open a serial console on a linux box ). The serial link sometimes becomes unresponsive and I have to physically unplug the USB-serial converter.

The below seems to solve my problem, but not always.

1. Find the driver associated to your ttyUSBx device.

   [my-pc]# cat /proc/tty/drivers

   /dev/tty             /dev/tty        5       0 system:/dev/tty
   /dev/console         /dev/console    5       1 system:console
   /dev/ptmx            /dev/ptmx       5       2 system
   /dev/vc/0            /dev/vc/0       4       0 system:vtmaster
   rfcomm               /dev/rfcomm   216 0-255 serial
   usbserial            /dev/ttyUSB   188 0-253 serial
   ttyprintk            /dev/ttyprintk   5       3 console
   serial               /dev/ttyS       4 64-111 serial
   pty_slave            /dev/pts      136 0-1048575 pty:slave
   pty_master           /dev/ptm      128 0-1048575 pty:master
   unknown              /dev/tty        4 1-63 console
   

   You can see that /dev/ttyUSB uses usbserial. Now dig a little further:

   [my-pc]# lsmod | grep usbserial

     usbserial              37173  1 pl2303
   

   In my case, my USB-to-serial converter is a Prolific PL2303. If you have a FTDI adapter, I think you should see ftdi_sio instead of pl2303.

2. Unload the driver

   sudo modprobe -r pl2303 #or the name that matches your config

   sudo modprobe -r usbserial

3. Re-load the driver

   sudo modprobe pl2303 #or the name that matches your config

4. Re-launch your serial communication

Answer 2

With sdive's answer I kept getting "FATAL: Module usbserial is in use."

I finally solved the problem with some guidance from LiLo's answer here: https://askubuntu.com/a/661/379851

But instead of using some C code, I wrote a python equivalent that also finds the bus and device in question:

#!/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

Just save this as reset_usb.py or something and then run it like this:

sudo python reset_usb.py driver_name

Where driver_name is the output from

lsmod | grep usbserial

In my case, it was cp210x, so I run it like this:

sudo python reset_usb.py cp210x

Answer 3

Here is my answer for the module ftdi_sio. Steps are adapted from the above answer and the link from a comment in the original question.

I could not get the module to be removed:

% sudo rmmod ftdi_sio
rmmod: ERROR: Module ftdi_sio is in use
% sudo modprobe -r ftdi_sio
modprobe: FATAL: Module ftdi_sio is in use.

So I use the following trick:

% sudo dmesg | grep ttyUSB0
[    4.784615] usb 3-2.4: FTDI USB Serial Device converter now attached to ttyUSB0

Which indeed was verified by:

% tree /sys/bus/usb/drivers/ftdi_sio     
/sys/bus/usb/drivers/ftdi_sio
├── 3-2.4:1.0 -> ../../../../devices/pci0000:00/0000:00:14.0/usb3/3-2/3-2.4/3-2.4:1.0
├── bind
├── module -> ../../../../module/usbserial
├── uevent
└── unbind

2 directories, 3 files

Then it was easy to remove the module:

# echo -n "3-2.4:1.0"  > /sys/bus/usb/drivers/ftdi_sio/unbind
# rmmod ftdi_sio 
# rmmod usbserial 

And then simply:

# modprobe ftdi_sio

This is not clear why ftdi_sio gets in such bad shape, maybe still be bug as in:

• https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a9fec7102f01f6464b19e13ffd9d8c48663379ad

But it seems kernel 4.9.20 still contains bad ftdi_sio module.