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List:       freebsd-hackers
Subject:    Re: USB, select/poll for ucom
From:       Bernd Walter <ticso () cicely12 ! cicely ! de>
Date:       2003-06-28 12:03:16
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On Sat, Jun 28, 2003 at 12:37:10PM +0300, Danny Braniss wrote:
> [...]
> > have fun.  the mindshare book is good.  however, it took me a long
> > time to get a usb 'aha' moment and understand its twisty maze was
> > really a workable design obscured by standardese...  I suspect it is a
> > problem in the usb chipset driver for the com part.  ttypoll just says
> > 'you have data in the buffer' so for some reason the data isn't making
> > into the tty buffer.
> > 
> > Warner
> 
> Im amazed at how some of you can write a driver based on the Spec. Docs!
> 
> here is a pearl i came across reading the USB spec for 1.1, page 43
> 
>       'The maximum allowable interrupt data payload
>        size is 64 bytes or less for full-speed.'

The device will tell you his personal limits for the given endpoint.
See wMaxPacketSize in usb_endpoint_descriptor_t.
The specs only tell you that a device can't tell >64 byte as the
maximum for an interrupt endpoint.

-- 
B.Walter                   BWCT                http://www.bwct.de
ticso@bwct.de                                  info@bwct.de

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