Linux USB Serial

Linux USB Serial

[Steven J. Ackerman]

Hello-

Looking to provide support under Linux for our device which implements
a USB virtual  serial port using the Communications Device Class.

The device enumerates and communicates correctly under Windows XP, 
and shows up under lsusb -v command as:

Bus 005 Device 005: ID 0c6a:0005  
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            2 Communications
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  idVendor           0x0c6a 
  idProduct          0x0005 
  bcdDevice            1.00
  iManufacturer           1 ACS
  iProduct                2 ACS-LCD-Color-320x240
  iSerial                 3 1.0
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           67
    bNumInterfaces          2
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0xc0
      Self Powered
    MaxPower              100mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         2 Communications
      bInterfaceSubClass     32 
      bInterfaceProtocol      0 
      iInterface              0 
      CDC Header:
        bcdCDC               1.10
      CDC ACM:
        bmCapabilities       0x02
          line coding and serial state
      CDC Union:
        bMasterInterface        0
        bSlaveInterface         1 
      CDC Call Management:
        bmCapabilities       0x00
        bDataInterface          1
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x83  EP 3 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0008  1x 8 bytes
        bInterval             255
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           2
      bInterfaceClass        10 CDC Data
      bInterfaceSubClass      0 Unused
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x01  EP 1 OUT
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            2
          Transfer Type            Bulk
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0040  1x 64 bytes
        bInterval               0
Device Status:     0x0000
  (Bus Powered)

However it does not show up without the -verbose option.

Trying to load the usbserial module to activate the device results in the 
following error:

FATAL: Module vendor=0x0c6a not found.

Can anyone provide assistance in how to troubleshoot why Linux is 
not happy with this USB device ?

Thank you,

Steven J. Ackerman, Consultant
ACS, Sarasota, FL
http://www.acscontrol.com
mailto:steve-I01wfHm1r9xGyKhy+UYuEA@public.gmane.org




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Re: Linux USB Serial

[Bjørn Mork]

"Steven J. Ackerman" <steve@acscontrol.com> writes:

>     Interface Descriptor:
>       bLength                 9
>       bDescriptorType         4
>       bInterfaceNumber        0
>       bAlternateSetting       0
>       bNumEndpoints           1
>       bInterfaceClass         2 Communications
>       bInterfaceSubClass     32 

Looks like your bInterfaceSubClass is nibble swapped.  It should be 0x02
for ACM, not 0x20.


Bjørn
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RE: Linux USB Serial

[Steven J. Ackerman]

Bjrn-

Thank you for your response.

This change gets me closer. I can now successfully execute the modprobe
without error, but the device still doesn't show up in /dev/ttyUSB? .

sja@UBUNTU-10:~$ sudo modprobe usbserial vendor=0x0c6a product=0x0005
sja@UBUNTU-10:~$ lsusb
Bus 005 Device 004: ID 0c6a:0005  
Bus 005 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 004 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 003 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 002 Device 003: ID 045e:0048 Microsoft Corp. Office Keyboard 1.0A
Bus 002 Device 002: ID 0557:7000 ATEN International Co., Ltd Hub
Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

I guess it's still not happy about something...

Steven J. Ackerman, Consultant
ACS, Sarasota, FL
http://www.acscontrol.com
mailto:steve@acscontrol.com


> -----Original Message-----
> From: Bjørn Mork [mailto:bjorn@mork.no]
> Sent: Monday, September 17, 2012 4:08 PM
> To: Steven J. Ackerman
> Cc: linux-usb@vger.kernel.org; linux-serial@vger.kernel.org
> Subject: Re: Linux USB Serial
> 
> "Steven J. Ackerman" <steve@acscontrol.com> writes:
> 
> >     Interface Descriptor:
> >       bLength                 9
> >       bDescriptorType         4
> >       bInterfaceNumber        0
> >       bAlternateSetting       0
> >       bNumEndpoints           1
> >       bInterfaceClass         2 Communications
> >       bInterfaceSubClass     32
> 
> Looks like your bInterfaceSubClass is nibble swapped.  It should be 0x02
> for ACM, not 0x20.
> 
> 
> Bjrn


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Re: Linux USB Serial

[Greg KH]

On Mon, Sep 17, 2012 at 05:07:26PM -0400, Steven J. Ackerman wrote:
> Bjrn-
> 
> Thank you for your response.
> 
> This change gets me closer. I can now successfully execute the modprobe
> without error, but the device still doesn't show up in /dev/ttyUSB? .
> 
> sja@UBUNTU-10:~$ sudo modprobe usbserial vendor=0x0c6a product=0x0005

Eeek, no, never do that with a device you actually want to use.  This
should be controlled by the cdc-acm driver, not the usbserial driver.
That driver should be auto-loaded for this device, but it looks like the
descriptor is wrong, so it's not binding to it.

Are you able to test a patch and rebuild the kernel to see if we can get
this to work properly?

thanks,

greg k-h

RE: Linux USB Serial

[Steven J. Ackerman]

Greg-

Thanks for your response.

Not sure if I need the cdc-acm functionality or not.

This is a color lcd display that supports a usb serial interface to
interact. I really 
just need to be able to send and receive characters and NAK the pipe back 
temporarily when my input buffer is full.

The descriptors were supplied by the chip vendor - Renesas - as part of a 
CDC demo application. The VID/PID is ours. The device works great under 
Windows XP with the descriptors as shown previously - even with the 
Communications bInterfaceSubClass value wrong.

Doing the modprobe, etc. was based upon some blog posts that purported
to show how to add support for an unknown usb serial device.

Looking at the descriptor for a FTDI USB serial to TTL cable it seems a lot
simpler,
but it does indicate vendor specific class, subclass and protocol - which
means 
that it requires a custom driver - ftdi_sio - right ?  I don't really want
to have to 
develop and support that.

I don't think that I have enough Linux experience to be able to test a patch

and rebuild of the kernel, and I don't think that I can ask my customers to
do 
that it order to use our product as a simple serial display.  

I'm running Ubuntu 10.10.

Any additional pointers and/or ideas would be greatly appreciated.

Thank you again,

Steven J. Ackerman, Consultant
ACS, Sarasota, FL
http://www.acscontrol.com
mailto:steve@acscontrol.com


> -----Original Message-----
> From: Greg KH [mailto:gregkh@linuxfoundation.org]
> Sent: Monday, September 17, 2012 5:42 PM
> To: Steven J. Ackerman
> Cc: 'Bjørn Mork'; linux-usb@vger.kernel.org; linux-serial@vger.kernel.org
> Subject: Re: Linux USB Serial
> 
> On Mon, Sep 17, 2012 at 05:07:26PM -0400, Steven J. Ackerman wrote:
> > Bjrn-
> >
> > Thank you for your response.
> >
> > This change gets me closer. I can now successfully execute the modprobe
> > without error, but the device still doesn't show up in /dev/ttyUSB? .
> >
> > sja@UBUNTU-10:~$ sudo modprobe usbserial vendor=0x0c6a
> product=0x0005
> 
> Eeek, no, never do that with a device you actually want to use.  This
> should be controlled by the cdc-acm driver, not the usbserial driver.
> That driver should be auto-loaded for this device, but it looks like the
> descriptor is wrong, so it's not binding to it.
> 
> Are you able to test a patch and rebuild the kernel to see if we can get
> this to work properly?
> 
> thanks,
> 
> greg k-h


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Re: Linux USB Serial

['Greg KH']

A: No.
Q: Should I include quotations after my reply?

http://daringfireball.net/2007/07/on_top

On Mon, Sep 17, 2012 at 05:56:46PM -0400, Steven J. Ackerman wrote:
> Greg-
> 
> Thanks for your response.
> 
> Not sure if I need the cdc-acm functionality or not.
> 
> This is a color lcd display that supports a usb serial interface to
> interact. I really 
> just need to be able to send and receive characters and NAK the pipe back 
> temporarily when my input buffer is full.

That's fine, the cdc-acm interface will work for that.

> The descriptors were supplied by the chip vendor - Renesas - as part of a 
> CDC demo application. The VID/PID is ours. The device works great under 
> Windows XP with the descriptors as shown previously - even with the 
> Communications bInterfaceSubClass value wrong.

But is your device really a CDC ACM device?  Or is it something else?

> Doing the modprobe, etc. was based upon some blog posts that purported
> to show how to add support for an unknown usb serial device.

Yes, but that's a one-off, and your kernel should have told you that you
shouldn't be doing that, if you are using a modern kernel release.

> Looking at the descriptor for a FTDI USB serial to TTL cable it seems a lot
> simpler,
> but it does indicate vendor specific class, subclass and protocol - which
> means 
> that it requires a custom driver - ftdi_sio - right ?  I don't really want
> to have to 
> develop and support that.

You wouldn't, if you use the ftdi serial chip in your device.  Which
begs me to ask, what type of usb to serial chip is in your device?  What
protocol does it use to talk to the host?

> I don't think that I have enough Linux experience to be able to test a patch
> and rebuild of the kernel, and I don't think that I can ask my customers to
> do that it order to use our product as a simple serial display.  

They shouldn't have to do that, once we get it working, they get the
update automatically from their distro.  But if you can't test any
changes we make to try to get this to work, there's not much we can do
here, right?

I think you need to figure out the protocol used by your device to talk
to the host.  If you get that worked out, we can help to get Linux
working with it.

Oh, and fix that descriptor up in your firmware, that might solve
everything :)

Hope this helps,

greg k-h
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RE: Linux USB Serial

[Steven J. Ackerman]

> That's fine, the cdc-acm interface will work for that.
> 
> But is your device really a CDC ACM device?  Or is it something else?

The device is a 3.5" color LCD display with touchscreen that can act as a
serial 
terminal. It just needs to be able to send and receive characters over an
USB
serial port.

> You wouldn't, if you use the ftdi serial chip in your device.  Which
> begs me to ask, what type of usb to serial chip is in your device?  What
> protocol does it use to talk to the host?

The device is based upon a Renesas RX62N processor which has a USB interface

in it.  The protocol is supposedly based upon the CDC - a control endpoint
and 
two bulk endpoints. The software was derived from a demo supplied by the 
manufacturer - and it does work under Windows. The device enumerates as 
a COM port and you can interact with the display using a program or a
terminal 
emulator.  Unfortunately the chip vendor doesn't have any support for Linux.

> They shouldn't have to do that, once we get it working, they get the
> update automatically from their distro.  But if you can't test any
> changes we make to try to get this to work, there's not much we can do
> here, right?
> 

I guess that I'm operating under the assumption that there is something 
wrong on my end - an incorrectly configured descriptor for example. It
appears 
the other USB serial devices work OK under Linux - even without custom 
drivers. I'm hoping that I can find an error message somewhere that will 
tell me what I'm doing wrong - or that somebody who has been down that 
path before can't point to something obvious - like Bjrn did.

> Oh, and fix that descriptor up in your firmware, that might solve
> everything :)

Going through the USB CDC documentation between e-mails. Other than 
the incorrect bInterfaceSubClass value - which I have corrected - nothing 
else seems wrong.

> 
> Hope this helps,
> 
> greg k-h

Always appreciate your assistance - thank you!


Steven J. Ackerman, Consultant
ACS, Sarasota, FL
http://www.acscontrol.com
mailto:steve@acscontrol.com

Re: Linux USB Serial

[Oliver Neukum]

On Monday 17 September 2012 17:07:26 Steven J. Ackerman wrote:
> Bjrn-
> 
> Thank you for your response.
> 
> This change gets me closer. I can now successfully execute the modprobe
> without error, but the device still doesn't show up in /dev/ttyUSB? .

It shouldn't. Your device follows the CDC ACM specification, aside from
the incorrect subclass. Such devices don't generate /dev/ttyUSB devices
nodes. They generate /dev/ttyACM nodes.

> sja@UBUNTU-10:~$ sudo modprobe usbserial vendor=0x0c6a product=0x0005

That is the wrong driver. usbserial is for vendor specific serial devices.
Your device follows a class specification. You need cdc_acm. As soon
as the subclass is fixed, it should autoload.

If cdc_acm doesn't bind, please post "dmesg".

	Regards
		Oliver

RE: Linux USB Serial

[Steven J. Ackerman]

> It shouldn't. Your device follows the CDC ACM specification, aside from
> the incorrect subclass. Such devices don't generate /dev/ttyUSB devices
> nodes. They generate /dev/ttyACM nodes.
> 

Thank you.  I did some more research on this last night and found out that 
I was being mis-lead by observing how other USB Serial devices were 
working and used under Linux - without having to install a driver.
Apparently 
these were all using the FTDI chip - and there is a driver that is already 
installed for them.

> That is the wrong driver. usbserial is for vendor specific serial devices.
> Your device follows a class specification. You need cdc_acm. As soon
> as the subclass is fixed, it should autoload.
> 

Yes - the driver now autoloads and I can communicate with the device 
using the /dev/ttyACM0 node. I was able to install picocom and talk to and 
from our display.

Thanks to everyone who replied to this question for your assistance.

Steven J. Ackerman, Consultant
ACS, Sarasota, FL
http://www.acscontrol.com
mailto:steve-I01wfHm1r9xGyKhy+UYuEA@public.gmane.org





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