From owner-freebsd-hackers@FreeBSD.ORG  Fri Jan 13 20:58:01 2012
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From: Hans Petter Selasky <hselasky@c2i.net>
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Date: Fri, 13 Jan 2012 21:55:45 +0100
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Message-Id: <201201132155.45324.hselasky@c2i.net>
Cc: Daniel Grech <dgre090@gmail.com>
Subject: Re: USB Zero length packet
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On Friday 13 January 2012 10:29:18 Daniel Grech wrote:
> Hi,
> 
> does anybody know what the procedure for sending a zero length packet
> through libusb on FreeBSD is ?
> 
> Thanks in advance,
> 
> Regards,
> 
> Daniel

By writing zero bytes, you send a zero length packet. With the libusb20 API 
you can set a flag to optimise this case in the kernel instead.

--HPS