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-----Original Message-----

As Rudolf says, why would you want to do this.  It really makes no sense and
in over 8 years of working with USB and 100's of devices, I have never seen
it used.

See other comments inline:

> -----Original Message-----
> From: usb-bounces@o... [mailto:usb-bounces@o...]On
> Behalf Of Rudolf Usselmann
> Sent: Monday, February 09, 2004 12:47 AM
> To: Discussion list about free, open source USB IP core
> Subject: Re: [usb] Help about
>
>
> On Mon, 2004-02-09 at 15:27, Lifeng Chen wrote:
> > Hi, Marc
> >
> > Thx for your kindly help :-)
> >
> > My question should be :  Is it possible to use SetDescriptor
> Request (but not GetDescriptor) to modify the Interface
> Descriptor. ? or is it recommended to do so ?
>
> Why not ?
>
> You can also use the vendor IO to modify your descriptors.
>
> However I do not see WHY you would want to do that.
>
> > Here "modify" means to modify the content of an interface
> descriptor, e.g., bNumEndpoints field .
> >
> >
> > Another problem: According to the USB2.0 spec, only 1 device is
> in presence. But what's the factual situation?  What's the
> general solution? Do we need multiple device descriptors in case
> of OTG development, where CBI/Bulk Only/Still Image/etc. Class
> are all potential devices? Alllowing the Application Software to
> implement multiple Device Descriptors and select an approximate
> one to respond to the host ? or 1 single Device Descriptor with
> multiple Configuration/Interface Descriptors ?
>
> One device ? Hmmm, not sure what you are referring. USB
> bus support up to 128 devices if I remember correctly.
> OTG on the other hand is a pure point to point connection
> and supports only one device AT A TIME.

Actually, it is 127 since address 0 is the default address for any device
until they are enumerated.  Practically, it is 126 since the root hub counts
as a device.  Really practically, I have never seen a host actually survive
the connection of more and a few dozen devices and still keep working ;=)

> There are descriptors for the entire interface and for
> each endpoint in every device.
>
> I don't understand what the confusion is ...
>
> OTG is only required to support specific devices. Thats
> more of a "deriver" issue ...
>
> Regards,
> rudi
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