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

[Jens T. T. <jt...@to...>]

Hi Tim,

On Thu, Apr 23, 2009 at 01:32:51PM -0700, Tim Roberts wrote:
> And have you tried 0x88, which is the actual endpoint address?

No, I didn't - I have misunderstood the meaning of "endpoint
address" and was assuming that passing it the end point number
does the trick. I will try this and hope that's going to fix
the problem.

> > 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.

I was guessing that this contradiction would be the reason, thanks
for confirming my suspicion. I just can hope that it will work in
the end anyway...

> 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.

I see, thank you!

               Thank you very mich and best regards, Jens
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