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 data sheets from Xirlink.
  
  Video formats:
        128x96  [model 1]
        176x144
        320x240 [model 2]
        352x240 [model 2]
        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:
  
  Xirlink "C-It" camera, also known as "IBM PC Camera".
  The device uses proprietary ASIC (and compression method);

  it is manufactured by Xirlink. See http://xirlinkwebcam.sourceforge.net, 
  http://www.ibmpccamera.com, or http://www.c-itnow.com/ for details and pictures.

  
  This very chipset ("X Chip", as marked at the factory)
  is used in several other cameras, and they are supported
  as well:
  
  - IBM NetCamera
  - Veo Stingray
  
  The Linux driver was developed with camera with following
  model number (or FCC ID): KSX-XVP510. This camera has three
  interfaces, each with one endpoint (control, iso, iso). This
  type of cameras is referred to as "model 1". These cameras are
  no longer manufactured.
  
  Xirlink now manufactures new cameras which are somewhat different.
  In particular, following models [FCC ID] belong to that category:
  
  XVP300 [KSX-X9903]
  XVP600 [KSX-X9902]
  XVP610 [KSX-X9902]
  
  (see http://www.xirlink.com/ibmpccamera/ for updates, they refer
  to these new cameras by Windows driver dated 12-27-99, v3005 BETA)
  These cameras have two interfaces, one endpoint in each (iso, bulk).
  Such type of cameras is referred to as "model 2". They are supported
  (with exception of 352x288 native mode).
  
  Some IBM NetCameras (Model 4) are made to generate only compressed
  video streams. This is great for performance, but unfortunately
  nobody knows how to decompress the stream :-( Therefore, these
  cameras are *unsupported* and if you try to use one of those, all
  you get is random colored horizontal streaks, not the image!
  If you have one of those cameras, you probably should return it
  to the store and get something that is supported.
  
  Tell me more about all that "model" business
  --------------------------------------------
  
  I just invented model numbers to uniquely identify flavors of the
  hardware/firmware that were sold. It was very confusing to use
  brand names or some other internal numbering schemes. So I found
  by experimentation that all Xirlink chipsets fall into four big
  classes, and I called them "models". Each model is programmed in
  its own way, and each model sends back the video in its own way.
  
  Quirks of Model 2 cameras:
  -------------------------
  
  Model 2 does not have hardware contrast control. Corresponding V4L
  control is implemented in software, which is not very nice to your
  CPU, but at least it works.
  
  This driver provides 352x288 mode by switching the camera into
  quasi-352x288 RGB mode (800 Kbits per frame) essentially limiting
  this mode to 10 frames per second or less, in ideal conditions on
  the bus (USB is shared, after all). The frame rate
  has to be programmed very conservatively. Additional concern is that
  frame rate depends on brightness setting; therefore the picture can
  be good at one brightness and broken at another! I did not want to fix
  the frame rate at slowest setting, but I had to move it pretty much down
  the scale (so that framerate option barely matters). I also noticed that
  camera after first powering up produces frames slightly faster than during
  consecutive uses. All this means that if you use 352x288 (which is
  default), be warned - you may encounter broken picture on first connect;
  try to adjust brightness - brighter image is slower, so USB will be able
  to send all data. However if you regularly use Model 2 cameras you may
  prefer 176x144 which makes perfectly good I420, with no scaling and
  lesser demands on USB (300 Kbits per second, or 26 frames per second).
  
  Another strange effect of 352x288 mode is the fine vertical grid visible
  on some colored surfaces. I am sure it is caused by me not understanding
  what the camera is trying to say. Blame trade secrets for that.
  
  The camera that I had also has a hardware quirk: if disconnected,
  it needs few minutes to "relax" before it can be plugged in again
  (poorly designed USB processor reset circuit?)
  
  [Veo Stingray with Product ID 0x800C is also Model 2, but I haven't
  observed this particular flaw in it.]
  
  Model 2 camera can be programmed for very high sensitivity (even starlight
  may be enough), this makes it convenient for tinkering with. The driver
  code has enough comments to help a programmer to tweak the camera
  as s/he feels necessary.
  
  WHAT YOU NEED:
  
  - A supported IBM PC (C-it) camera (model 1 or 2)
  
  - A Linux box with USB support (2.3/2.4; 2.2 w/backport may work)
  
  - 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 ibmcam driver uses usbvideo helper library (module),
  so if you are studying the ibmcam code you will be led there.
  
  The driver itself consists of only one file in usb/ directory:
  ibmcam.c. This file is 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.
  
  To begin with, on most modern Linux distributions the driver
  will be automatically loaded whenever you plug the supported
  camera in. Therefore, you don't need to do anything. However
  if you want to experiment with some module parameters then
  you can load and unload the driver manually, with camera
  plugged in or unplugged.
  
  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: (* indicates that option is model-dependent)
  
  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
  hue_correction  Integer         0-255 [128]     hue_correction=115
  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
  size            Integer         0-2* [2]        size=1
  
  Options for Model 2 only:
  
  Name            Type            Range [default] Example
  --------------  --------------  --------------  ------------------
  init_model2_rg  Integer         0..255 [0x70]   init_model2_rg=128
  init_model2_rg2 Integer         0..255 [0x2f]   init_model2_rg2=50
  init_model2_sat Integer         0..255 [0x34]   init_model2_sat=65
  init_model2_yb  Integer         0..255 [0xa0]   init_model2_yb=200
  
  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.
  		FLAGS_SEPARATE_FRAMES   32 Shows each frame separately, as
  					   it was received from the camera.
  					   Default (not set) is to mix the
  					   preceding frame in to compensate
  					   for occasional loss of Isoc data
  					   on high frame rates.
  		FLAGS_CLEAN_FRAMES      64 Forces "cleanup" of each frame
  					   prior to use; relevant only if
  					   FLAGS_SEPARATE_FRAMES is set.
  					   Default is not to clean frames,
  					   this is a little faster but may
  					   produce flicker if frame rate is
  					   too high and Isoc data gets lost.
  		FLAGS_NO_DECODING      128 This flag turns the video stream
  					   decoder off, and dumps the raw
  					   Isoc data from the camera into
  					   the reading process. Useful to
  					   developers, but not to users.

  
  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.

  
  hue_correction  This highly optional setting allows to adjust the

  		hue of the image in a way slightly different from
  		what usual "hue" control does. Both controls affect
  		YUV colorspace: regular "hue" control adjusts only
  		U component, and this "hue_correction" option similarly
  		adjusts only V component. However usually it is enough
  		to tweak only U or V to compensate for colored light or
  		color temperature; this option simply allows more
  		complicated correction when and if it is necessary.

  
  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.

  
  init_model2_rg  These initial settings alter color balance of the
  init_model2_rg2 camera on hardware level. All four settings may be used
  init_model2_sat to tune the camera to specific lighting conditions. These
  init_model2_yb  settings only apply to Model 2 cameras.
  
  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). The
  		Model 2 cameras allow values more than 2 for this option,
  		thus enabling extremely high sensitivity at cost of frame
  		rate, color saturation and imaging sensor noise.

  
  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. Model 2
  		cameras do not support this feature.

  
  size            This setting chooses one of several image sizes that are

  		supported by this driver. Cameras may support more, but
  		it's difficult to reverse-engineer all formats.
  		Following video sizes are supported:
  
  		size=0     128x96  (Model 1 only)
  		size=1     160x120
  		size=2     176x144
  		size=3     320x240 (Model 2 only)
  		size=4     352x240 (Model 2 only)
  		size=5     352x288
  		size=6     640x480 (Model 3 only)
  
  		The 352x288 is the native size of the Model 1 sensor
  		array, so it's the best resolution the camera can
  		yield. The best resolution of Model 2 is 176x144, and
  		larger images are produced by stretching the bitmap.
  		Model 3 has sensor with 640x480 grid, and it works too,
  		but the frame rate will be exceptionally low (1-2 FPS);
  		it may be still OK for some applications, like security.
  		Choose the image size you need. The smaller image can
  		support faster frame rate. Default is 352x288.

  
  For more information and the Troubleshooting FAQ visit this URL:

  		http://www.linux-usb.org/ibmcam/

  
  WHAT NEEDS TO BE DONE:
  
  - The button on the camera is not used. I don't know how to get to it.
    I know now how to read button on Model 2, but what to do with it?
  
  - 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. This is mostly Model 1
    concern because Model 2 uses different commands which do not return
    status (and seem to complete successfully every time).
  
  - Some flavors of Model 4 NetCameras produce only compressed video
    streams, and I don't know how to decode them.
  
  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.
  
  I also thank John Lightsey for his donation of the Veo Stingray camera.