> On Fr, 2011-04-15 at 19:39 +0200, Alexey Fisher wrote:
> > Hallo all,
> >
> > here is patch (against current master git) to add two new quirks and
> > some more debug string to see what happening :D
> >
> > The quirks are:
> > UVC_QUIRK_FIX_JPEG_BANDWIDTH 0x00000040
> > /* to recalculate bandwidth needed for jpeg compressed stream */
> > UVC_QUIRK_DISABLE_URB_1024 0x00000400
> > /* by default we use safe bandwith restriction, to less than 1024 *
> > * this quirk disables this restriction. So if you need URB less than
> > * 1024, use this quirk. It will work only with FIX*BANDWIDTH quirk. */
> >
> > Also i added module option "jpeg_comp" to change calculation for
> > bandwith. Default is 4bpp, 1 is maximal compression, 16bpp is no
> > compression, just normal raw stream.
> >
> > This patch also gather statistic about used buffers. It will report
> > biggest used buffer. You will need it to calculate best value for
> > jpeg_comp option.
> >
> > Usage. Recalculate bandwidth for jpeg and disable 1024 restriction:
> > sudo rmmod uvcvideo && sudo modprobe quirks=0x440
> >
> > reduce calculated bandwith to minimum:
> > sudo rmmod uvcvideo && sudo modprobe quirks=0x440 jpeg_comp=1
> >
> > for more info enable trace=0xffff and seek for messages like:
> > ...
> > [25495.869580] uvcvideo: Device requested 703 B/frame bandwidth.
> > [25495.869583] uvcvideo: Selecting alternate setting 5 (800 B/frame
> > bandwidth).
> > [25495.869758] uvcvideo: Allocated 5 URB buffers of 32x800 bytes each.
> > ...
> > [25501.959475] uvcvideo: Biggest used buffer: 1382400/106438. Format:
> > MJPEG 960x720@15.
> >
Lets continue the conversation hier :D it is the proper place for it.
> Hi Alexey,
>
> On Friday 15 April 2011 19:43:38 Alexey Fisher wrote:
> > There is new patch. With this patch you can recalculate bandwith for
> > jpeg stream. See my post in list and try it:
> > [patch] jpeg compression hacks. Tester are welcome!!!
>
> Now I understand what your patch is for :-)
>
> One issue that you forgot to take into account is that, in addition to
> average
> bandwidth requirements, cameras also have peak bandwidth requirements.
> At low
> frame rates, an image could be transmitted with a lower bandwidth, but
> that
> would require buffering capabilities on the camera side to store the
> image and
> transmit it over a longer period of time. Most cameras have very
> little buffer
> memory, and thus require a high bandwidth even at low frame rates.
> Depending
> on the hardware MJPEG encoder, the average bandwidth for a frame will
> not
> match the peak bandwidth requirements.
I thick you mean this part of code:
- bandwidth = max_t(u32, bandwidth, 1024);
+ if(!(stream->dev->quirks & UVC_QUIRK_DISABLE_URB_1024))
+ bandwidth = max_t(u32, bandwidth, 1024);
but i did it optional. User who has good cam can try to use unsafe
option. May be i need to mark it "highly dangerous, use on your own
risk!!!" :)
--
Regards,
Alexey
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