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[Discuss-gnuradio] mmap()ed USB interface

From: Harald Welte
Subject: [Discuss-gnuradio] mmap()ed USB interface
Date: Sun, 1 May 2005 21:18:19 +0200
User-agent: mutt-ng 1.5.8-r168i (Debian)

On Sun, May 01, 2005 at 08:27:34PM +0200, Harald Welte wrote:

> I was also thinking of speeding up the USB data transfers by using a
> better kernel/userspace interface than libusb (which does
> copy_{from,to}_user for every URB).  Something like a mmap()ed
> ringbuffer comes to mind, much like the mmap() feature of AF_PACKET or
> the PF_RING socket.   But that's probably one of the things that would
> be nice and I never find the time to implement...

After doing some research on the EHCI hardware interface, this looks
very promising.  The situation is even better than networking.  USB2
should allow us to mmap() a buffer into userspace, and setup EHCI qtd's
that directly point into that mmap()ed buffer.

in other words: direct dma to userspace, real zerocopy.

Of course this is only superficially related to usrp, but rather
something like a generic usbdevfs-mmap extension.  I'll contact the
linux-usb kernel developers and see whether they might have any comments
on that.

- Harald Welte <address@hidden>                         http://gnumonks.org/
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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