Re: [Linux-uvc-devel] How to 'quirk' more than 3 same "YUYV" streaming web-cams

[Laurent P. <lau...@id...>]

On Tuesday 29 March 2011 14:59:52 Alexey Fisher wrote:
> Am Montag, den 28.03.2011, 20:26 +0400 schrieb "Клиентский отдел
> 
> \"Кибернет\"":
> > Hi.
> > 
> > I'm using zoneminder server to record events from usb uvcvideo web-cams.
> > 
> > 3 same A4tech PK-836MJ works well with 352x288 yuyv streaming if I
> > modify /sys/module/uvcvideo/parameters/quirks to 128.
> > 
> > But I unable to attach more webcams. These cams have no mjpeg. Could
> > anybody help me to apply quirks or recalculate bandwith to use more
> > webcams. As I understood "no space on left device" message depends on
> 
> i assume it mean your hard drive. uvcvideo do not have this kind of
> message.
> 
> > total bandwith utilisation of my usb hub. There is no other root usb 2.0
> > hubs on my motherboard. I'm use 2.6.36-gentoo-r8 kernel. I explore
> > /drivers/media/video/uvc. As I understand, the camera reports that it
> > can much better resolutiont than 640x480x24bit with 30fps. Is it
> > possible to manualy decrease bandwith of these cameras? Or maybe it is
> > possible to patch uvc_video.c?
> 
> can you please send more info about this cam. "lsusb -v" will be good
> start.
> 
> USB 2.0 theoretically can handle 480 Mbit/s. RAW yuyv (depends on
> resolution and frame rate) will  need say: 640x480 at 30fps (16bpp) =
> 140 Mbit/s .  So, theoretically you can use 3,4 cams. DO not forget a
> real usb bandwidth and uvc overhead.

Periodical transfers are limited to 80% of the USB bandwidth, so you're 
limited to 2.74 640x480 @30fps streams (not including UVC and USB overhead).

> If you need more cams, you need reduce resolution and/or frame rate. Not
> all webcams support different frame rates.

-- 
Regards,

Laurent Pinchart