On Thu, 12 Dec 2013, Tim Roberts wrote:
> Hans de Goede wrote:
> >
> > "the isoc endpoint is only created when changing to alt setting 1"
> >
> > Ah, that is what saves your bacon then, most devices have the isoc eps
> > in altsetting 0 too, with a maxpacketsize of 0.
> >
>
> No, they don't. Or at least they aren't supposed to. Alt setting 0
> should not contain any isochronous endpoints at all. Having an endpoint
> with a max packet size of 0 is silly.
I agree that it is silly, but the spec does permit it. At the end of
section 5.6.3 in the USB-2.0 spec, it says:
All device default interface settings must not include any
isochronous endpoints with non-zero data payload sizes
(specified via wMaxPacketSize in the endpoint descriptor).
Alternate interface settings may specify non-zero data payload
sizes for isochronous endpoints
ALan Stern
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