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From: Hans Petter Selasky <hselasky@c2i.net>
To: freebsd-arm@freebsd.org
Subject: Re: Isochronous USB transfers on RPI?
Date: Wed, 16 Jan 2013 13:19:17 +0100
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Cc: Jakob Alvermark <jakob@alvermark.net>
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On Wednesday 16 January 2013 10:25:38 Jakob Alvermark wrote:
> Hi,
> 
> Maybe this should go to the usb list, but it is probably relevant here as
> well. I have been playing with the Pi for a while now and having great fun
> with FreeBSD. Great work gonzo and others!
> However, I'd like to use a webcam with it. I learned that USB webcams use
> isochronous transfers and the DWC OTG driver doesn't fully implement it.
> (If I read the commit logs correctly)
> What is missing and how can I help?
> 

Hi,

The DWC OTG driver has not fully implemented isochronous. Using isochronous 
transfers will have a high CPU load impact, because 1000 IRQ's (FS) or 8000 
IRQ's (HS) second will be needed to feed the FIFOs. However, if this is 
acceptable, code can be found in:

sys/dev/usb/controller/dwc_otg.c

--HPS