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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 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://www.xirlink.com/
+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.