Re: VirtualSerial: Device or resource busy

[Johannes H. Jensen]

Replying to myself in case someone else stumble into the same.

It turns out it was a permission problem, something I didn't even consider given the dubious error message! Running minicom as root works, so all I need to do now is set up a .rules file[1].

Thanks goes to "Opendous Support", whoever you are, who was kind enough to send me the answer by e-mail :-)

[1] http://code.google.com/p/micropendous/wiki/SerialPortUsageLinux#Setting_Up_Serial_Port_Security

Cheers,

- Johannes

On Wednesday, January 16, 2013 12:34:35 AM UTC+1, Johannes H. Jensen wrote:

Greetings!

I'm trying to get the Device/ClassDriver/VirtualSerial demo running on my "Pro Micro" ATmega32U4 board[1].

The board has no joystick, so I've commented out the Joystick code and replaced the call to CheckJoystickMovement() with:

fputs("Hello world\r\n", &USBSerialStream);

I.e. my attempt is to have an endless stream of "Hello world" messages printed to the serial device on my Linux machine.

The device seems to enumerate successfully. I see the following in dmesg:

[ 1719.756322] usb 1-1.3: new full-speed USB device number 27 using ehci_hcd
[ 1719.843258] cdc_acm 1-1.3:1.0: ttyACM0: USB ACM device

However, when I attempt to open /dev/ttyACM0 with minicom, all I get is "Device or resource busy":

$ minicom -b 9600 -D /dev/ttyACM0 
minicom: cannot open /dev/ttyACM0: Device or resource busy

Fuses read:

avrdude: Device signature = 0x1e9587

avrdude: safemode: lfuse reads as DE
avrdude: safemode: hfuse reads as 99
avrdude: safemode: efuse reads as C3

I'm running Ubuntu 12.10 with the 3.5.0 Linux kernel.

Any hints on what might be wrong?

Cheers,

- Johannes

[1] https://www.sparkfun.com/products/11098

[Johannes H. Jensen]

Replying to myself again...

Turns out setting the permissions with an udev rule is not enough, at least on Ubuntu 12.10. Turns out a daemon called 'modem-manager' will try to open any new serial device it encounters. This prevents any other program from opening the serial device. Check syslog for clues like:

Jan 21 23:27:49 FarSite modem-manager[6970]: <info>  (ttyACM0) opening serial port...

Jan 21 23:27:56 FarSite modem-manager[6970]: <info>  (ttyACM0) closing serial port...

Jan 21 23:27:56 FarSite modem-manager[6970]: <info>  (ttyACM0) serial port closed

Jan 21 23:27:56 FarSite modem-manager[6970]: <warn>  Couldn't probe for capabilities, probably not a GSM or CDMA modem

To prevent this, you can add the following to the udev rule: ENV{ID_MM_DEVICE_IGNORE}="1", e.g.

SUBSYSTEM=="usb", ATTR{idVendor}=="1b4f", ATTR{idProduct}=="9205", MODE="0660", GROUP="plugdev", ENV{ID_MM_DEVICE_IGNORE}="1"

Cheers,

- Johannes

[Don Davis]

Wow are they trying to become more apple like?

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[Stefan Hellermann]

Happens on Fedora, too! Seems they probe every CDC device to know if
it's an mobile broadband modem.

2013/1/22 Don Davis <ddelma...@gmail.com>:

[Marcin Szczodrak]

Thanks Johannes.

This worked for me with a similar problem with Ubuntu 13.10. I was attaching UCMote Proton B and the /dev/ttyACM0 was getting busy for ~35 seconds after plugging in, because of the modem-manager. 

Just to keep it public, for UCMote Proton B, the udev rule to save in

/etc/udev/rules.d/55-ucprotonb.rules 

is

SUBSYSTEM=="usb", ATTR{idVendor}=="04d8", ATTR{idProduct}=="00df", MODE="0660", GROUP="plugdev", ENV{ID_MM_DEVICE_IGNORE}="1"

-Marcin

[László Monda]

The modem manager suckage is actually a known problem documented at
https://github.com/abcminiuser/lufa/blob/master/Bootloaders/CDC/BootloaderCDC.txt

Sorry for not replying earlier and saving some pain.

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László Monda <http://Monda.hu> | <http://UltimateHackingKeyboard.com>