Re: [Libusb-devel] ENOENT on read from device

[Tim R. <ti...@pr...>]

Jens Thoms Toerring wrote:
> j) On trying to read the reply the device is supposed to send
>
>    libusb_bulk_transfer( udev, 8, readbuf, 64, &cnt, 0 );
>
>    the call fails returns -1 and the debug output is
>
>    libusb:error [submit_bulk_transfer] submiturb failed error -1 errno=2
>   

And have you tried 0x88, which is the actual endpoint address?

> Now there's something in the 'dmesg' output for
> the device that looks a bit suspicious to me but which I am not
> sure if it's relevant:
>
> usb 1-3: new high speed USB device using ehci_hcd and address 17
> usb 1-3: config 1 interface 0 altsetting 0 bulk endpoint 0x2 has invalid maxpacket 64
> usb 1-3: config 1 interface 0 altsetting 0 bulk endpoint 0x4 has invalid maxpacket 64
> usb 1-3: config 1 interface 0 altsetting 0 bulk endpoint 0x86 has invalid maxpacket 64
> usb 1-3: config 1 interface 0 altsetting 0 bulk endpoint 0x88 has invalid maxpacket 64
> usb 1-3: configuration #1 chosen from 1 choice
> usb 1-3: New USB device found, idVendor=184c, idProduct=0000
> usb 1-3: New USB device strings: Mfr=1, Product=2, SerialNumber=3
> usb 1-3: Product: Clear Shot II Camera
> usb 1-3: Manufacturer: Centice Corporation
> usb 1-3: SerialNumber: 0000044
>
> In contrast to this output the documentation for the camera expli-
> citely says that 64 is the max packet size for all endpoints. Could
> this explain why reading from the device fails with ENOENT? (But
> why is a writing data to it working then?)
>   

No, but this device violates the USB spec.  It is allowing itself to be
recognized as a high-speed device (see first line), and bulk endpoints
on a high speed device MUST have a max packet size of 512.  That a
device error, plain and simple.

Note that it is quite possible for a device to be a USB 2.0 device and
still enumerate only as full-speed.

> Finally one more question out of mere curiosity: how does one
> deduce from the device data if a configuration is low, full or
> high speed? Is all one can go by the maximum packet size or is
> this information somewhere in the output of lsusb and I'm just
> too stupid to figure it out?
>   

This information is not present in the descriptors.  If the bcdUSB value
is 1.xx, then you know it cannot be high-speed, but that's really as far
as you can go.  You can look in /proc/bus/usb/devices, if it is turned on.

-- 
Tim Roberts, ti...@pr...
Providenza & Boekelheide, Inc.