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Philips webcams (pwc driver)
This file contains some additional information for the Philips and OEM webcams.
E-mail: Last updated: 2004-01-19
As of this moment, the following cameras are supported:
* Philips PCA645
* Philips PCA646
* Philips PCVC675
* Philips PCVC680
* Philips PCVC690
* Philips PCVC720/40
* Philips PCVC730
* Philips PCVC740
* Philips PCVC750
* Askey VC010
* Creative Labs Webcam 5
* Creative Labs Webcam Pro Ex
* Logitech QuickCam 3000 Pro
* Logitech QuickCam 4000 Pro
* Logitech QuickCam Notebook Pro
* Logitech QuickCam Zoom
* Logitech QuickCam Orbit
* Logitech QuickCam Sphere
* Samsung MPC-C10
* Samsung MPC-C30
* Sotec Afina Eye
* AME CU-001
* Visionite VCS-UM100
* Visionite VCS-UC300
The main webpage for the Philips driver is at the address above. It contains
a lot of extra information, a FAQ, and the binary plugin 'PWCX'. This plugin
contains decompression routines that allow you to use higher image sizes and
framerates; in addition the webcam uses less bandwidth on the USB bus (handy
if you want to run more than 1 camera simultaneously). These routines fall
under a NDA, and may therefore not be distributed as source; however, its use
is completely optional.
You can build this code either into your kernel, or as a module. I recommend
the latter, since it makes troubleshooting a lot easier. The built-in
microphone is supported through the USB Audio class.
When you load the module you can set some default settings for the
camera; some programs depend on a particular image-size or -format and
don't know how to set it properly in the driver. The options are:
Can be one of 'sqcif', 'qsif', 'qcif', 'sif', 'cif' or
'vga', for an image size of resp. 128x96, 160x120, 176x144,
320x240, 352x288 and 640x480 (of course, only for those cameras that
support these resolutions).
Specifies the desired framerate. Is an integer in the range of 4-30.
This parameter specifies the number of internal buffers to use for storing
frames from the cam. This will help if the process that reads images from
the cam is a bit slow or momentarily busy. However, on slow machines it
only introduces lag, so choose carefully. The default is 3, which is
reasonable. You can set it between 2 and 5.
This is an integer between 1 and 10. It will tell the module the number of
buffers to reserve for mmap(), VIDIOCCGMBUF, VIDIOCMCAPTURE and friends.
The default is 2, which is adequate for most applications (double
Should you experience a lot of 'Dumping frame...' messages during
grabbing with a tool that uses mmap(), you might want to increase if.
However, it doesn't really buffer images, it just gives you a bit more
slack when your program is behind. But you need a multi-threaded or
forked program to really take advantage of these buffers.
The absolute maximum is 10, but don't set it too high! Every buffer takes
up 460 KB of RAM, so unless you have a lot of memory setting this to
something more than 4 is an absolute waste. This memory is only
allocated during open(), so nothing is wasted when the camera is not in
When power_save is enabled (set to 1), the module will try to shut down
the cam on close() and re-activate on open(). This will save power and
turn off the LED. Not all cameras support this though (the 645 and 646
don't have power saving at all), and some models don't work either (they
will shut down, but never wake up). Consider this experimental. By
default this option is disabled.
compression (only useful with the plugin)
With this option you can control the compression factor that the camera
uses to squeeze the image through the USB bus. You can set the
parameter between 0 and 3::
0 = prefer uncompressed images; if the requested mode is not available
in an uncompressed format, the driver will silently switch to low
1 = low compression.
2 = medium compression.
3 = high compression.
High compression takes less bandwidth of course, but it could also
introduce some unwanted artefacts. The default is 2, medium compression.
See the FAQ on the website for an overview of which modes require
The compression parameter does not apply to the 645 and 646 cameras
and OEM models derived from those (only a few). Most cams honour this
This settings takes 2 integers, that define the on/off time for the LED
(in milliseconds). One of the interesting things that you can do with
this is let the LED blink while the camera is in use. This::
will blink the LED once every second. But with::
the LED never goes on, making it suitable for silent surveillance.
By default the camera's LED is on solid while in use, and turned off
when the camera is not used anymore.
This parameter works only with the ToUCam range of cameras (720, 730, 740,
750) and OEMs. For other cameras this command is silently ignored, and
the LED cannot be controlled.
Finally: this parameters does not take effect UNTIL the first time you
open the camera device. Until then, the LED remains on.
A long standing problem with USB devices is their dynamic nature: you
never know what device a camera gets assigned; it depends on module load
order, the hub configuration, the order in which devices are plugged in,
and the phase of the moon (i.e. it can be random). With this option you
can give the driver a hint as to what video device node (/dev/videoX) it
should use with a specific camera. This is also handy if you have two
cameras of the same model.
A camera is specified by its type (the number from the camera model,
like PCA645, PCVC750VC, etc) and optionally the serial number (visible
in /sys/kernel/debug/usb/devices). A hint consists of a string with the
following format::
The square brackets mean that both the type and the serialnumber are
optional, but a serialnumber cannot be specified without a type (which
would be rather pointless). The serialnumber is separated from the type
by a '.'; the node number by a ':'.
This somewhat cryptic syntax is best explained by a few examples::
dev_hint=3,5 The first detected cam gets assigned
/dev/video3, the second /dev/video5. Any
other cameras will get the first free
available slot (see below).
dev_hint=645:1,680:2 The PCA645 camera will get /dev/video1,
and a PCVC680 /dev/video2.
dev_hint=645.0123:3,645.4567:0 The PCA645 camera with serialnumber
0123 goes to /dev/video3, the same
camera model with the 4567 serial
gets /dev/video0.
dev_hint=750:1,4,5,6 The PCVC750 camera will get /dev/video1, the
next 3 Philips cams will use /dev/video4
through /dev/video6.
Some points worth knowing:
- Serialnumbers are case sensitive and must be written full, including
leading zeroes (it's treated as a string).
- If a device node is already occupied, registration will fail and
the webcam is not available.
- You can have up to 64 video devices; be sure to make enough device
nodes in /dev if you want to spread the numbers.
After /dev/video9 comes /dev/video10 (not /dev/videoA).
- If a camera does not match any dev_hint, it will simply get assigned
the first available device node, just as it used to be.
In order to better detect problems, it is now possible to turn on a
'trace' of some of the calls the module makes; it logs all items in your
kernel log at debug level.
The trace variable is a bitmask; each bit represents a certain feature.
If you want to trace something, look up the bit value(s) in the table
below, add the values together and supply that to the trace variable.
====== ======= ================================================ =======
Value Value Description Default
(dec) (hex)
====== ======= ================================================ =======
1 0x1 Module initialization; this will log messages On
while loading and unloading the module
2 0x2 probe() and disconnect() traces On
4 0x4 Trace open() and close() calls Off
8 0x8 read(), mmap() and associated ioctl() calls Off
16 0x10 Memory allocation of buffers, etc. Off
32 0x20 Showing underflow, overflow and Dumping frame On
64 0x40 Show viewport and image sizes Off
128 0x80 PWCX debugging Off
====== ======= ================================================ =======
For example, to trace the open() & read() functions, sum 8 + 4 = 12,
so you would supply trace=12 during insmod or modprobe. If
you want to turn the initialization and probing tracing off, set trace=0.
The default value for trace is 35 (0x23).
# modprobe pwc size=cif fps=15 power_save=1
The fbufs, mbufs and trace parameters are global and apply to all connected
cameras. Each camera has its own set of buffers.
size and fps only specify defaults when you open() the device; this is to
accommodate some tools that don't set the size. You can change these
settings after open() with the Video4Linux ioctl() calls. The default of
defaults is QCIF size at 10 fps.
The compression parameter is semiglobal; it sets the initial compression
preference for all camera's, but this parameter can be set per camera with
the VIDIOCPWCSCQUAL ioctl() call.
All parameters are optional.