Hi,
On 12/07/2010 09:01 PM, Mauro Carvalho Chehab wrote:
Hi Jean-Fronçois,
git commit 35680baa6822df98a6ed602e2380aa0a04e18b07 (see enclosed) caused not
only a regression
at PS/3 Eye webcam (git commit f43402fa55bf5e7e190c176343015122f694857c), but
also at sn9c201 driver,
when used on SXGA mode. What happens is that only the highest alternate mode is
enough for the
maximum resolution.
I suspect that other drivers broke due to that change. So, IMO, the better is
to revert and work
on another alternative.
I have to agree with Mauro here, dropping back to a lower alt setting for all
devices with a usb
audio interface is the wrong thing to do.
For example I know multiple devices where the highest alt setting does not have
a wMaxPacketSize
of 1023, but use something lower instead, to make sure there is enough
bandwidth left for usb audio
even if the highest alt setting get used.
Btw, no matter what resolution is used, sn9c201 is setting the same alternate
for all modes,
spending more USB bandwidth than needed. Why gspca is just getting the highest
value for
wMaxPacketSize? It should, instead, seek for the minimum packet size that is
needed for a
given resolution.
There are 2 reasons for this:
1) We do not know the minimum packetsize for a given resolution, unlike with
uvc where this
is arranged in the protocol, for proprietary apps we can only guess
2) Almost all devices supported by gspca are usb-1.1 and thus the framerate is
bandwidth
limited. We want to deliver the highest framerate possible, and thus get as
high an alt
setting as possible.
I most note that many gspca subdrivers are defective wrt how this is all
handled though, in
that they don't vary the framerate when the available bandwidth changes. So in
many cases if
the gspca core cannot get the highest alt setting things may not function at
all (because the
subdriver fails to select a lower framerate, resulting in parts of frames
getting dropped
due to bandwidth limitations).
Fixing this requires:
1) Figuring out how to change the framerate for each sensor + bridge combo
2) Testing to see what framerate will still work at which alt setting
Regards,
Hans
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