linux-kernel - Re: [linux-usb-devel] [USB] urb->number_of

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Date:	Mon, 27 Nov 2006 10:03:02 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Duncan Sands <duncan.sands@...h.u-psud.fr>
cc:	Ilyes Gouta <ilyes.gouta@...il.com>,
	<linux-usb-devel@...ts.sourceforge.net>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [linux-usb-devel] [USB] urb->number_of_packets = 256 !

On Mon, 27 Nov 2006, Duncan Sands wrote:

> Hi Ilyes, you won't be able to allocate that much *contiguous* memory,
> but you should be able to allocate enough non-contiguous memory (e.g.
> by calling __get_free_page 256 times; not the same as calling
> __get_free_pages(8) !).  To use that memory, you can try using the usb
> scatter/gather support (see usb.h); I don't know if it works with
> isochronous urbs though.  I've CC'd the usb development list - maybe
> someone there can help.

The scatter/gather library does not support iso.

> > Splitting the transfer across multiple URB doesn't seem to work (I didn't really
> > investigate in depth this possibility).

It should work.  Go back and try it again more carefully.

Alan Stern

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