faq.html

Linux support for Philips USB webcams halted Latest version: pwc-9.0.2.tar.gz (including documents

<p>Sometimes when the camera is plugged in, its image controls are stuck to
some unusable state. Normally it has auto-exposure on and adjusts for
different lighting conditions (daytime, fluorescent light, etc).

<p>The only way to get this camera &quot;unstuck&quot; electronically is
with CamStream at the moment. In the video controls dialog, there is a
&quot;Reset to Factory Settings&quot; button. In 95% of the cases this
does the trick. Unfortunately, there is currently no way to do it
from a command line utility (I should probably make one), or have the
camera reset every time it is opened.


<h3><a name="L6">I get some USB message about "device not accepting address" when loading the module, and it doesn't work...</a></h3>

<p>Read this <a href="install.html#common">part in the Installation
notes</a> about it. Basicly, it's not problem.</p>


<h3><a name="R9">Everything loads fine, but I just get a black image with all the utilities I tried</a></h3>

<p>In case you have an UHCI controller, try using the usb-uhci.o module, and
not the uhci.o module. I'm having trouble with uhci.o too. The usb-uhci.o
module is built when you select <b>USB support -&gt; UHCI Intel PIIX4, VIA,
...</b> in your kernel.


<h3><a name="Q12">Why are the PCA635, PCVC665 (Vesta Fun) and PCVC720 (ToUCam XS) not supported by your driver?</a></h3>

<p>The answer is simple: Philips doesn't make them. This may come as a shock
to you, but it is quite common with computer hardware. These cameras are so
called OEM products: some manufacturer develops a piece of hardware, and
offers it for sale. Some other company (like Philips) then decides to buy
these devices in large quantities, stamps their label on it, puts them in a
box and sells them as their own, including warranty and support.

<p>However, with these deals the hardware specifications are rarely sold
with the device. Thus, Philips does not even have the documentation
themselves to give to me.<br>
The reverse also happens: Philips sells their hardware to others who
repackage it or design a camera around it; this explains the large number
of &quot;strange&quot; cameras supported by this driver.</p>

<p>But, not all is lost. The PVCV665 actually has a driver (see the main
page for the link), based on its chipset. Something is happening for
the PCVC720 too (again, link is on the main page).</p>

<p>The PCA635 is not supported because it is not a USB cam; it has a
parallel port interface.

<h3><a name="Q14">Should I always use the do-it-yourself package?</a></h3>

<p>Good question, which gets asked quite a lot. The answer is: if the binary
module works for you, don't bother. However, if the module goes Oops, hangs,
produces weird images or lots of debug messages, then by all means try it.</p>

<p>The do-it-yourself package should in theory fit your kernel better, since
it is compiled with the same options and compiler as your own kernel. Some
things in the kernel are dependant on the compiler version and this could
introduce a binary incompatibility. But in general, what I compile works on
most kernels. Also, the do-it-yourself package does not offer any advantage
in speed or functionality.</p>

<h3><a name="R10">I only get a very small picture within an enormous black/gray area</a></h3>

<p>You forgot to install and/or load the <a href="release.html#pwcx">pwcx.o module</a>.</p>


<h3><a name="Q15">I want to set an exposure time of 2 minutes for my astronomy
observations. Is this possible?</a></h3>

<p>Only with a hardware modification. Yes, that means heating up a soldering
iron, opening your webcam case and poke around the tiny SMD components with
tiny wires. In other words, not recommended. If you are willing to take the
risk, you can look at these <a
href="http://home.clara.net/smunch/iintro.htm">instructions</a> done by
Steve Chambers.

<p>The camera is quite sensitive however (that's why I get asked this
question quite a lot), and by playing with the settings I mentioned about
you can probably get a decent shot of the moon and some planets; but don't
expect miracles. If you really want to do serious astronomy with an
electronic camera I suggest you buy one of the commercially available CCD
sensors (some may even have Linux drivers). Or submit your resume at NASA :)</p>


<h3><a name="Q16">The driver from kernel &gt;= 2.4.5 doesn't work anymore with tool XYZ.</a></h3>

<p>Correct. With the inclusion of the driver in the standard kernel (version
7.0) Alan Cox <a href="driver-reject.html">insisted</a> that all the palette
conversion stuff be removed from the driver. The result is that 90% of the
tools didn't work anymore. Blame Alan, and contact the writer of your tool to
have it fixed, not me. The only palette currently supported by the driver is
VIDEO_PALETTE_YUV420P.</p>

<p>The good news is that virtually all tools work with the PWC
driver again; see the <a href="working.html">Working stuff</a> page
for what's known to work. The most notable exception is RealProducer
Basic.</p>

<h3><a name="Q17">I don't have /proc/bus/usb/devices!</a></h3>

<p>A yes... One day I'm going to have a word with the nitwit who decided
that the USB information should not be available to the user unless he/she
really requests it... Use this command:</p>

<p><pre>
	# mount -t usbdevfs none /proc/bus/usb  
</pre></p>



<h3><a name="Q18">Can you help me with a driver for Novell/OS2/Win CE/MacOS X?</a></h3>

<p>No. There is a MacOS X driver, however.</p>


<h3><a name="L7">PWCX complains about version mismatch</a></h3>

<p>The pwcx module was compiled on 2.4.6, so it won't load immediately on
anything else. But you can force the module in with insmod like this:</p>

<p><pre>
insmod --force /lib/modules/usb/pwcx.o
</pre></p>


<h3><a name="L8">Is there a way to automatically load PWCX after the PWC module?</a></h3>

<p>Yes, there is! John Rodkey sent me a tip; add this to your <b>/etc/modules.conf</b>:</p>

<p><pre>
post-install pwc /sbin/insmod --force /lib/modules/usb/pwcx-i386.o >/dev/null 2>&amp;1  || :
</pre></p>

<p>You may of course have to change the path to the pwcx module, depending
on your setup. Now everytime pwc is loaded (either by modprobe or the
kerneld), pwcx will loaded too. You will need the --force option because the
pwcx kernel version will probably not match yours. And oh, since pwcx is
kernel independant, you should indeed install it in <b>/lib/modules/usb</b>, instead
of <b>/lib/modules/&lt;kernel-version&gt;/kernel/drivers/usb</b>.</p>



<h3><a name="I5">Where should I install the pwcx.o module? After each kernel upgrade I have to copy it again to /lib/modules.</a></h3>

<p>You should copy the pwcx.o module to <b>/lib/modules/usb</b>; this
directory is specifically set up for kernel-independant/external modules,
and modprobe will look in this directory too. See also the item about
<a href="#L8">automatic loading of PWCX</a>.</p>


<h3><a name="R12">My image is mirrored</a></h3>

<p>This seems to happen with the PCVC730 and the Logitech cam; I have seen
it myself, and it has been reported a number of times. Unfortunately I
don't have a solution, and even the folks at Philips aren't sure what the
problem is... </p>

<p>Of course that doesn't help you a lot, but at least you know you're not
alone :-)</p>

<p>There have been a number of requests to make a 'mirror' option for the 
module. That is certainly possible, but that would require modifications
to the PWCX module as well, including a new major number. Eventually, it 
will happen, no worries :)</p>


<h3><a name="I6">I have no clue as how to configure my RedHat/Suse/Mandrake/Oompa-Loompa Linux distribution. Why don't you write step-by-step instructions on what I must do?</a></h3>


<p>Because then I would spend all day writing such step-by-step instructions 
for every imaginable Linux distribution and version out there. And next you're
going to ask me to translate it as well, including Oompa-Loompa...</p>

<p>The observant reader will detect a hint of sarcasm in the above
paragraph. But there is another reason: step-by-step instructions probably
aren't going to help you much if you don't know what you're doing. And if
something is missing from your installation or some other unexpected error
occurs, you'll probably be stuck anyway. The best advice I can give you
in this case is to ask a friend who has more knowledge about Linux and
help you with the installation, and observe what they are doing.</p>

<p>Now I know that this sounds a bit like 'I know it all but I'm not going
to tell you anything'. The point is: I don't know much. Not about the
current Linux distributions anyway. And I think you should learn how to do
your basic Linux stuff first before you attempt something like upgrading
your kernel, which isn't that difficult, but still a bit tricky...</p>




<h3><a name="L9">Modutils complains that PWCX is 'tainting' the kernel.
What's up?</a></h3>

<p>Nothing to worry about; since 2.4.something, kernel modules are required
to have a license type encoded in the module, similiar to the kernel version
number. This is because the Linux kernel is based on the GNU GPL (General
Public License), and some kernel developers feel that all modules that are
loaded in the kernel should be GPL 'licensed' too, so that's why this check
is built into modutils. However, since PWCX is based on an NDA and closed
source, it cannot be released as a GPL module. So I put in another text for
the license type, and that's why modutils complains.</p>

<p>Fortunately, this does not affect the working of the module in any way;
it is just a reminder that the module you're loading isn't 100% GPL 'pure'. 
To most people this doesn't matter; as long as it works without much hassle
they don't care. But some people insist on having a 100% pure GPL system,
so they are warned, and probably do not wish to use the PWCX module.</p>

<p>If you want to know my personal opinion of this tactic, you're
invited to read my editorial <a href="tainting.html#personal">&quot;Tainting
the kernel&quot;</a>.</p>


<h3><a name="L10">PWC(X) won't load because of 'unresolved symbols'</a></h3>

<p>If you can't load pwcx.o because of these messages:</p>

<p><pre>
depmod: *** Unresolved symbols in /lib/modules/usb/pwcx.o
depmod:         pwc_unregister_decompressor
depmod:         pwc_register_decompressor
depmod:         printk
</pre></p>

<p>then you have a kernel with <b>version information on module symbols</b>
turned <b>on</b>. Recompile and/or install a kernel with this option turned 
off. And yes, that is the only way.</p>

<p>If pwc.o (without x) doesn't load because of these missing functions:</p>

<p><pre>
  pwc.o: unresolved symbol video_register_device
  pwc.o: unresolved symbol video_unregister_device
</pre></p>

<p>you forgot to load and/or build the <b>videodev.o</b> module. However, on
newer systems this should almost never be the case. If this doesn't work
or you have other missing functions, you have a problem :)</p>


<h3><a name="R13">I want to hook up 10 cameras and take high resolution snapshots from them in succession. Is this possible?</a></h3>

<p>Presently, no. The reason is that the cameras are built for streaming
data, not stills. There's no way to pause the image stream easily so you can
take snapshots at a whim. The only method is to open the camera device, take
a snapshot and close it again, then go to the next.</p>



<h3><a name="R14">What does &quot;interrupt, status 2, frame #####&quot; mean?</a></h3>

<p>I have absoltely no idea. But if these kind of errors crop up regularely
and cause problems:</p>

<p><pre>usb-uhci.c: interrupt, status 2, frame# 1625</pre></p>

<p>then you may have a problem with your USB controller. Exactly what,
I can't tell you; but there is one common pattern: (heavy) IDE disk access.
This is what I wrote to somebody in a mail recently:</p>

<p><pre>
I think the main problem is timing and PCI bandwidth hogging. USB is quite
allergic to delays in its handling of incoming packets, or at least under
Linux. In addition, PWC can send quite large USB frames (up to 960
bytes/frame). Now, as soon as the USB controller receives a packet it will
try to send it to the computer's main memory, and to do so, it has to send
the data over the PCI bus (the USB controller is usually a PCI busmaster);
this can happen several hundred times per second. Now, with all these IDE
UltraDMA 33/66/100/133 disks and controllers, it's quite possible the IDE
disk hogs the PCI bus long enough for the USB transfer to fail. I think
that in the BIOS on most motherboards the IDE controller gets a way higher
priority than the USB controller. In the past I've suggested trying to play
with the latency of PCI devices with the 'setpci' utility, however without
any definite results.
</pre></p>


<p>So there. Either way, it's not my (or PWC) problem; you should write to the
authors of the UHCI and OHCI controller drivers, they may be able to
tell you what's wrong.</p>

<p>However, before you innundate them with email, try the following first:
<ul>
  <li>Try the latest kernel available, it may be solved already;</li>
  <li>Check if the USB controller shares an IRQ with other devices; if so,
      try to switch IRQs;</li>
  <li>Try using a powered hub for your webcam; there could be a power
      consumption issue, unstable voltages, et cetera;</li>
  <li>bad cabling;</li>
</ul>
</p>

<p>Before you really start mailing these guys, make sure you can reproduce the
problem. Unreproducable errors simply cannot be solved.</p>

<p>Note: the Philips webcams use isochronuous USB tranfers, which are not reliable.
This means that if a bad or corrupted USB frame arrives, it is discarded and no
retransmission is attempted. So it's quite normal for the PWC driver to drop a
video frame or two.</p>


<h3><a name="L11">PWCX won't load because of 'invalid module format'</a></h3>

<p>The 2.6 kernels use a new (binary) format for their modules; the module
files now end in '.ko', in stead of '.o'. This new format is incompatible
with the old one, so you can't load old versions of PWCX. I suggest you use
the new <a href="release.html#pwcx9">PWCX 9 module</a>. You will need
PWC/PWCX 9 anyway for kernel 2.6.7 and higher.</p>


<h3><a name="I7">I have trouble using the webcam on an ARM system</a></h3>

<p>Before you continue, you should check with the manufacturer of your ARM 
board if the on-board USB controller can support large ISOC transfers. 
Some boards do not support isochronuous transfers at all, others are limited
to a maximum of 240 bytes. Although theoretically some modes of the PWC 
cams use a framesize &lt; 240 bytes, it does not always seem to work.</p>

<p>Before you contact me, check if your USB controller on your board
supports ISOC transfers up to 1024 bytes. If not, PWC cannot work on your
system.</p>


<h3><a href="R15">I have triple vision!</a></h3>

<p>In case you don't get a color image but a grayscale image that is
repeated three times on a row, the program you are using does not support
the VIDEO_PALETTE_YUV420P palette. Contact the author of the program.
Or stop drinking so much :-)</p>


<p><a href="index.html">Back to the main page</a></p>

<hr>

<h6><i>2004-07-15 - Nemosoft Unv.</i></h6>

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