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README for Linux device driver for the IBM "C-It" USB video camera
INTRODUCTION:
This driver does not use all features known to exist in
the IBM camera. However most of needed features work well.
This driver was developed using logs of observed USB traffic
which was produced by standard Windows driver (c-it98.sys).
I did not have any input from Xirlink. Some people asked about
data sheets, but nothing came out of that. I didn't try.
Video formats: 128x96, 176x144, 352x288
Frame rate: 3 - 30 frames per second (FPS)
External interface: USB
Internal interface: Video For Linux (V4L)
Supported controls:
- by V4L: Contrast, Brightness, Color, Hue
- by driver options: frame rate, lighting conditions, video format,
default picture settings, sharpness.
SUPPORTED CAMERAS:
IBM "C-It" camera, also known as "Xirlink PC Camera"
The device uses proprietary ASIC (and compression method);
it is manufactured by Xirlink. See http://www.xirlink.com
WHAT YOU NEED:
- An IBM C-it camera
- A Linux box with USB support (2.3/2.4 or 2.2 w/backport)
- A Video4Linux compatible frame grabber program such as xawtv.
HOW TO COMPILE THE DRIVER:
You need to compile the driver only if you are a developer
or if you want to make changes to the code. Most distributions
precompile all modules, so you can go directly to the next
section "HOW TO USE THE DRIVER".
The driver consists of two files in usb/ directory:
ibmcam.c and ibmcam.h These files are included into the
Linux kernel build process if you configure the kernel
for CONFIG_USB_IBMCAM. Run "make xconfig" and in USB section
you will find the IBM camera driver. Select it, save the
configuration and recompile.
HOW TO USE THE DRIVER:
I recommend to compile driver as a module. This gives you an
easier access to its configuration. The camera has many more
settings than V4L can operate, so some settings are done using
module options.
Typically module is installed with command 'modprobe', like this:
# modprobe ibmcam framerate=1
Alternatively you can use 'insmod' in similar fashion:
# insmod /lib/modules/2.x.y/usb/ibmcam.o framerate=1
Module can be inserted with camera connected or disconnected.
The driver can have options, though some defaults are provided.
Driver options:
Name Type Range [default] Example
-------------- -------------- -------------- ------------------
debug Integer 0-9 [0] debug=1
flags Integer 0-0xFF [0] flags=0x0d
framerate Integer 0-6 [2] framerate=1
init_brightness Integer 0-255 [128] init_brightness=100
init_contrast Integer 0-255 [192] init_contrast=200
init_color Integer 0-255 [128] init_color=130
init_hue Integer 0-255 [128] init_hue=115
lighting Integer 0-2 [1] lighting=2
sharpness Integer 0-6 [4] sharpness=3
videosize Integer 0-2 [2] videosize=1
debug You don't need this option unless you are a developer.
If you are a developer then you will see in the code
what values do what. 0=off.
flags This is a bit mask, and you can combine any number of
bits to produce what you want. Usually you don't want
any of extra features this option provides:
FLAGS_RETRY_VIDIOCSYNC 1 This bit allows to retry failed
VIDIOCSYNC ioctls without failing.
Will work with xawtv, will not
with xrealproducer. Default is
not set.
FLAGS_MONOCHROME 2 Activates monochrome (b/w) mode.
FLAGS_DISPLAY_HINTS 4 Shows colored pixels which have
magic meaning to developers.
FLAGS_OVERLAY_STATS 8 Shows tiny numbers on screen,
useful only for debugging.
FLAGS_FORCE_TESTPATTERN 16 Shows blue screen with numbers.
framerate This setting controls frame rate of the camera. This is
an approximate setting (in terms of "worst" ... "best")
because camera changes frame rate depending on amount
of light available. Setting 0 is slowest, 6 is fastest.
Beware - fast settings are very demanding and may not
work well with all video sizes. Be conservative.
init_brightness These settings specify _initial_ values which will be
init_contrast used to set up the camera. If your V4L application has
init_color its own controls to adjust the picture then these
init_hue controls will be used too. These options allow you to
preconfigure the camera when it gets connected, before
any V4L application connects to it. Good for webcams.
lighting This option selects one of three hardware-defined
photosensitivity settings of the camera. 0=bright light,
1=Medium (default), 2=Low light. This setting affects
frame rate: the dimmer the lighting the lower the frame
rate (because longer exposition time is needed).
sharpness This option controls smoothing (noise reduction)
made by camera. Setting 0 is most smooth, setting 6
is most sharp. Be aware that CMOS sensor used in the
camera is pretty noisy, so if you choose 6 you will
be greeted with "snowy" image. Default is 4.
videosize This setting chooses one if three image sizes that are
supported by this driver. Camera supports more, but
it's difficult to reverse-engineer all formats.
Following video sizes are supported:
videosize=0 128x96
videosize=1 176x144
videosize=2 352x288
The last one (352x288) is the native size of the sensor
array, so it's the best resolution camera can yield.
Choose the image size you need. The smaller image can
support faster frame rate. Default is 352x288.
WHAT NEEDS TO BE DONE:
- The box freezes if working camera (with xawtv) is unplugged (OHCI).
Workaround: don't do that :) End the V4L application first.
- Some USB frames are lost on high frame rates, though they shouldn't
- ViCE compression (Xirlink proprietary) may improve frame rate
- On occasion camera does not start properly; xawtv reports errors.
Workaround: reload the driver module. Reason: [1].
- On occasion camera produces negative image (funny colors.)
Workaround: reload the driver module. Reason: [1].
- The button on the camera is not used. I don't know how to get to it.
[1]
- Camera reports its status back to the driver; however I don't know
what returned data means. If camera fails at some initialization
stage then something should be done, and I don't do that because
I don't even know that some command failed.
CREDITS:
The code is based in no small part on the CPiA driver by Johannes Erdfelt,
Randy Dunlap, and others. Big thanks to them for their pioneering work on that
and the USB stack.
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