OPENCORES.ORG

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

The spec has it.  You only have one device descriptor.  You are really
making this more complex than it has to be.

Use a single device descriptor and multiple configuration or interface
descriptors as appropriate for your specific application.  Don't try to out
guess or stretch the spec, follow it.  The other path leads to madness and
worse ;=)

Marc Reinig
System Solutions

> -----Original Message-----
> From: usb-bounces@o...
> [mailto:usb-bounces@o...]On Behalf Of Lifeng Chen
> Sent: Monday, February 09, 2004 1:06 AM
> To: rudi@a...; Discussion list about free,open source USB IP core
> Subject: Re: [usb] Help about
>
>
> 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" 
> To: "Discussion list about free, open source USB IP core"
> 
> 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
> > ========================================================
> >    ASICS.ws   ::: Solutions for your ASIC/FPGA needs :::
> > ..............::: FPGAs * Full Custom ICs * IP Cores :::
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> >
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>
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