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 separted 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.

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