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On Mon, 2004-02-09 at 15:27, Lifeng Chen wrote:

Dear Rudi,
Excuse me for my carelessness. //blush.  What I meant should be a single "device descriptor" rather than "device" for my OTG controller.
Now I'd like to repeat my question here:
According to the USB2.0 spec, only 1 device DESCRIPTOR is in presence. But what's the factual situation?  What's the general solution? Do we need multiple device descriptors in case of OTG DEVICE 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 ?

Best Rgds,
-------------------------------
Joe
----- Original Message ----- 
From: "Rudolf Usselmann" <rudi@a...>
To: "Discussion list about free, open source USB IP core" <usb@o...>
Sent: Monday, February 09, 2004 4:47 PM
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.
> 
> 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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