Re: [Libusb-devel] Why does Linux forget the USB toggle bit of mydevice?

[Ludovic R. <lud...@gm...>]

2009/3/30 Alan Stern <st...@ro...>:
> On Mon, 30 Mar 2009, Mike Nuss wrote:
>
>> Ludovic Rousseau wrote:
>> > >
>> > > The driver works fine the first time I launch it. The problem is
>> when
>> > > I restart it. Using a USB hardware spy I discovered that each time I
>> > > start my driver the first USB frame sent is always using DATA0 (USB
>> > > toggle bit). The problem is my USB device may be expecting a DATA1
>> > > frame and will not answer this DATA0 frame.
>
> Kernel versions prior to 2.6.28 will always send a Set-Interface
> request when your program releases its interface (or when it closes the
> device file).  If the device doesn't support this request then the
> kernel sends Clear-Halt for each endpoint in the interface.  These
> requests are supposed to set the data toggle back to 0, but many
> devices don't support them properly.
>
>> Try set_configuration. The USB 2.0 spec requires the device to reset the
>> data toggle for any non-zero set_configuration request (section
>> 9.1.1.5).
>
> Set-Config is also rather heavy-handed.  Furthermore, the USB spec also
> requires devices to reset the data toggle in response to Set-Interface
> or Clear-Halt (section 9.4.5) --  devices don't always follow the spec.

My USB device does not support the CLEAR_FEATURE and respond with an error.
It looks like this behavior is supported by USB 2.0 specification:
9.4.1 Clear Feature
"A ClearFeature() request that references a feature that cannot be
cleared, that does not exist, or that references an interface or
endpoint that does not exist, will cause the device to respond with a
Request Error."

Maybe the Linux kernel could NOT reset its toggle bit if the
ClearFeature(ENDPOINT_HALT) fails?

> The best answer may be to upgrade to 2.6.28 or 2.6.29.

That would be a long term solution. I am using Linux 2.6.26 from
Debian stable and need to support a lot of other Linux distributions.

Note that I have the same problem on Mac OS X. So I have to "correct"
my code or the device firmware.

Thanks a lot for the very informative answers.

-- 
 Dr. Ludovic Rousseau