USB isochronous transfers

[John Birrell]

Are there any USB experts here?

The ugen driver in current has code that treats an isochronous endpoint
which has a wMaxPacketSize of zero as invalid and won't open it.

I have a board here that reports it's isochronous endpoint like that.

On page 47 of the USB Specification 2.0, I see this:

"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 operation."

My board is supposed to be a reference implementation from Philips
for their 1581 USB chip and their MPEG2 chips. It only has the default
interface.

The board seems to behave like the specification says it should. FreeBSD's
ugen implementation seems to be the odd one out.

Does anyone know what to expect from a device with wMaxPacketSize = 0?

-- 
John Birrell