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Message
From: Rudolf Usselmann<rudi@a...>
Date: Mon Feb 9 09:47:10 CET 2004
Subject: [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.
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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