Re: [Spca50x-devs] (Re)design of gspca-v4l2
- Date: Tue, 08 Apr 2008 13:33:54 +0200
- From: Jean-Francois Moine <moinejf@xxxxxxx>
- Subject: Re: [Spca50x-devs] (Re)design of gspca-v4l2
On Sun, 30 Mar 2008 11:46:33 +0200, Hans de Goede <j.w.r.degoede@xxxxxx>
>The current design, which queues urbs for later processing in the application
>kernel context when a read or dqbuf call is made. Has one big advantage, the
>urb_complete handler which gets called in bottom half interrupt context is
>It however also has several big drawbacks:
You are right. In the last version, I changed the code so the transfer
URB packet to application frame is done at interrupt level. As there is
no decoding, the overhead is small.
>Problems with the suggested design: what todo with processing which needs to be
>done on the raw isoc packet data before being suitable for userspace.
>1) Don't, always feed raw data (frame aligned by checking for sof's but
> otherwise raw) to userspace.
[snip other solutions]
>After having written this all down, I believe I've answered my own question
>with with regards howto solve the processing of raw data problem, the answer I
>believe is method 3.
I think that only the solution 1 can be done. Decoding the frames is
the job of the (so awaited) v4l2 library!
BTW, without this library, a v4l2 helper extension must exist. Instead
of having a generic helper, as developped by Thierry Merle, I think
that the (main) gspca driver could implement a particular device, say
/dev/gspca_ext which could do pixfmt negociation and frame translation
with specific ioctls.
An other idea is to develop a usermode driver which uses a
vloopback-like device and the usblib. Such a driver could re-use the
same code (hear: without source change, only with a different
compilation) so that extending the supported webcam set could be easy
and any video application will work.
Ken ar c'hentañ | ** Breizh ha Linux atav! **
Jef | http://moinejf.free.fr/
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