Re: My Microdia (SN9C201) webcam doesn't work properly in Linux anymore

[Jean-Francois Moine <moinejf@free.fr>]

On Mon, 05 Mar 2012 09:33:18 +0100
Hans de Goede <hdegoede@redhat.com> wrote:

> I guess that motion is using the JPG compressed frames rather then
> the i420 like special format these cameras also support, and it looks
> like we don't reserve enoug space to buffer these frames. To fix this
> we need to enlarge the size we reserve per frame in the sn9c20x driver,
> edit sn9c20x.c and search for vga_mode, in that table you will
> find a factor "4 / 8" (its in there 3 times), change all 3 occurences
> to "5 / 8" and try again, then "6 / 8", etc.
> 
> Normally I would be suspicious about SOF / EOF detection when we
> need such a factor, but the timestamps in your log exactly match 30
> fps, so that seems to be fine. And in my experience with the USB bandwidth
> stuff the sn9c20x does seem to compress less then other JPG cams, so
> it makes sense that it needs bigger buffers to store the frames too.

Hi Hans,

The JPEG compression quality of the sn9c20x is 95%. That's why the
frames are so big. Then, if the quality is not settable, I wonder why
to use the JPEG format.

BTW, I wonder also about the SN9C20X_I420: this format asks for a
buffer greater than the native image. So, as these webcams are USB 2.0,
shouldn't it be simpler to have only Bayer in the driver?

-- 
Ken ar c'hentañ	|	      ** Breizh ha Linux atav! **
Jef		|		http://moinejf.free.fr/