On Wed, May 2, 2012 at 6:54 PM, Xiaofan Chen <xiaof...@gmail.com> wrote:
> On Thu, May 3, 2012 at 4:31 AM, Hans Petter Selasky <hsela...@c2i.net>
> wrote:
> > On Wednesday 02 May 2012 21:15:27 Tim Roberts wrote:
> >> Hans Petter Selasky wrote:
> >> > Why Microsoft can't use the BSD or Linux USB stack then, which
> supports
> >> > all of this. Sounds like very bad internal USB design to me!
> >>
> >> Oh, please. The Microsoft internal USB design is fine, and kernel
> >> drivers can do ALL of the things in that post. The restrictions
> >> mentioned in that list apply to WinUSB, which is the user-mode wrapper.
> >
> > In the answers from the Microsoft guy, there were some arguments about
> > security. Many kind of device drivers could have been made more secure by
> > moving out of the kernel, for example webcam drivers, which is a class of
> > devices which are especially using a lot of isochronous endpoints. The
> use
> > case is there for sure, but probably nobody saw it.
>
> I've seen many arguments about user space driver versus kernel
> space driver but I do not sell a very clear conclusions, for example
> on the webcam drivers. I see that Linux and Windows use
> kernel space driver for them. Do you think libusb based
> user space driver is good for USB Webcam?
>
It probably comes down to the number of kernel/user space transitions are
required. Certainly, you don't want to make an OS call per *isochronous
packet *see
http://msdn.microsoft.com/en-us/library/windows/hardware/hh406225%28v=vs.85%29.aspx.
That would then beg the question as to the user/kernel mode API and
its
ability to return status for each and every packet as well as the data
itself.
For such as a webcam, I'd think a higher level API is more appropriate -
along the lines of "give me a frame" rather than give me the next data from
the device... so a kernel driver may well be a better bet.
Orin.
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