1$Id: README,v 1.7 2005/08/29 23:39:57 sbertin Exp $
   31. Introduction
   5        This is a driver for STMicroelectronics's CPiA2 (second generation
   6Colour Processor Interface ASIC) based cameras. This camera outputs an MJPEG
   7stream at up to vga size. It implements the Video4Linux interface as much as
   8possible.  Since the V4L interface does not support compressed formats, only
   9an mjpeg enabled application can be used with the camera. We have modified the
  10gqcam application to view this stream.
  12        The driver is implemented as two kernel modules. The cpia2 module
  13contains the camera functions and the V4L interface.  The cpia2_usb module
  14contains usb specific functions.  The main reason for this was the size of the
  15module was getting out of hand, so I separated them.  It is not likely that
  16there will be a parallel port version.
  19   - Supports cameras with the Vision stv6410 (CIF) and stv6500 (VGA) cmos
  20     sensors. I only have the vga sensor, so can't test the other.
  21   - Image formats: VGA, QVGA, CIF, QCIF, and a number of sizes in between.
  22     VGA and QVGA are the native image sizes for the VGA camera. CIF is done
  23     in the coprocessor by scaling QVGA.  All other sizes are done by clipping.
  24   - Palette: YCrCb, compressed with MJPEG.
  25   - Some compression parameters are settable.
  26   - Sensor framerate is adjustable (up to 30 fps CIF, 15 fps VGA).
  27   - Adjust brightness, color, contrast while streaming.
  28   - Flicker control settable for 50 or 60 Hz mains frequency.
  302. Making and installing the stv672 driver modules:
  32        Requirements:
  33        -------------
  34        This should work with 2.4 (2.4.23 and later) and 2.6 kernels, but has
  35only been tested on 2.6.  Video4Linux must be either compiled into the kernel or
  36available as a module.  Video4Linux2 is automatically detected and made
  37available at compile time.
  39        Compiling:
  40        ----------
  41        As root, do a make install.  This will compile and install the modules
  42into the media/video directory in the module tree. For 2.4 kernels, use
  43Makefile_2.4 (aka do make -f Makefile_2.4 install).
  45        Setup:
  46        ------
  47        Use 'modprobe cpia2' to load and 'modprobe -r cpia2' to unload. This
  48may be done automatically by your distribution.
  503. Driver options
  52        Option          Description
  53        ------          -----------
  54        video_nr        video device to register (0=/dev/video0, etc)
  55                        range -1 to 64.  default is -1 (first available)
  56                        If you have more than 1 camera, this MUST be -1.
  57        buffer_size     Size for each frame buffer in bytes (default 68k)
  58        num_buffers     Number of frame buffers (1-32, default 3)
  59        alternate       USB Alternate (2-7, default 7)
  60        flicker_freq    Frequency for flicker reduction(50 or 60, default 60)
  61        flicker_mode    0 to disable, or 1 to enable flicker reduction.
  62                        (default 0). This is only effective if the camera
  63                        uses a stv0672 coprocessor.
  65        Setting the options:
  66        --------------------
  67        If you are using modules, edit /etc/modules.conf and add an options
  68line like this:
  69        options cpia2 num_buffers=3 buffer_size=65535
  71        If the driver is compiled into the kernel, at boot time specify them
  72like this:
  73        cpia2.num_buffers=3 cpia2.buffer_size=65535
  75        What buffer size should I use?
  76        ------------------------------
  77        The maximum image size depends on the alternate you choose, and the
  78frame rate achieved by the camera.  If the compression engine is able to
  79keep up with the frame rate, the maximum image size is given by the table
  81        The compression engine starts out at maximum compression, and will
  82increase image quality until it is close to the size in the table.  As long
  83as the compression engine can keep up with the frame rate, after a short time
  84the images will all be about the size in the table, regardless of resolution.
  85        At low alternate settings, the compression engine may not be able to
  86compress the image enough and will reduce the frame rate by producing larger
  88        The default of 68k should be good for most users.  This will handle
  89any alternate at frame rates down to 15fps.  For lower frame rates, it may
  90be necessary to increase the buffer size to avoid having frames dropped due
  91to insufficient space.
  93                             Image size(bytes)
  94        Alternate  bytes/ms   15fps    30fps
  95            2         128      8533     4267
  96            3         384     25600    12800
  97            4         640     42667    21333
  98            5         768     51200    25600
  99            6         896     59733    29867
 100            7        1023     68200    34100
 102        How many buffers should I use?
 103        ------------------------------
 104        For normal streaming, 3 should give the best results.  With only 2,
 105it is possible for the camera to finish sending one image just after a
 106program has started reading the other.  If this happens, the driver must drop
 107a frame.  The exception to this is if you have a heavily loaded machine.  In
 108this case use 2 buffers.  You are probably not reading at the full frame rate.
 109If the camera can send multiple images before a read finishes, it could
 110overwrite the third buffer before the read finishes, leading to a corrupt
 111image.  Single and double buffering have extra checks to avoid overwriting.
 1134. Using the camera
 115        We are providing a modified gqcam application to view the output. In
 116order to avoid confusion, here it is called mview.  There is also the qx5view
 117program which can also control the lights on the qx5 microscope. MJPEG Tools
 118( can also be used to record from the camera.
 1205. Notes to developers:
 122   - This is a driver version stripped of the 2.4 back compatibility
 123     and old MJPEG ioctl API. See for 2.4 support.
 1256. Thanks:
 127   - Peter Pregler <>,
 128     Scott J. Bertin <>, and
 129     Jarl Totland <> for the original cpia driver, which
 130     this one was modelled from.
 131 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.