146 lines
5.5 KiB
ReStructuredText
146 lines
5.5 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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The cpia2 driver
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================
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Authors: Peter Pregler <Peter_Pregler@email.com>,
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Scott J. Bertin <scottbertin@yahoo.com>, and
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Jarl Totland <Jarl.Totland@bdc.no> for the original cpia driver, which
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this one was modelled from.
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Introduction
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------------
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This is a driver for STMicroelectronics's CPiA2 (second generation
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Colour Processor Interface ASIC) based cameras. This camera outputs an MJPEG
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stream at up to vga size. It implements the Video4Linux interface as much as
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possible. Since the V4L interface does not support compressed formats, only
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an mjpeg enabled application can be used with the camera. We have modified the
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gqcam application to view this stream.
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The driver is implemented as two kernel modules. The cpia2 module
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contains the camera functions and the V4L interface. The cpia2_usb module
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contains usb specific functions. The main reason for this was the size of the
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module was getting out of hand, so I separated them. It is not likely that
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there will be a parallel port version.
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Features
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--------
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- Supports cameras with the Vision stv6410 (CIF) and stv6500 (VGA) cmos
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sensors. I only have the vga sensor, so can't test the other.
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- Image formats: VGA, QVGA, CIF, QCIF, and a number of sizes in between.
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VGA and QVGA are the native image sizes for the VGA camera. CIF is done
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in the coprocessor by scaling QVGA. All other sizes are done by clipping.
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- Palette: YCrCb, compressed with MJPEG.
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- Some compression parameters are settable.
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- Sensor framerate is adjustable (up to 30 fps CIF, 15 fps VGA).
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- Adjust brightness, color, contrast while streaming.
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- Flicker control settable for 50 or 60 Hz mains frequency.
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Making and installing the stv672 driver modules
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-----------------------------------------------
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Requirements
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~~~~~~~~~~~~
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Video4Linux must be either compiled into the kernel or
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available as a module. Video4Linux2 is automatically detected and made
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available at compile time.
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Setup
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~~~~~
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Use ``modprobe cpia2`` to load and ``modprobe -r cpia2`` to unload. This
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may be done automatically by your distribution.
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Driver options
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~~~~~~~~~~~~~~
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.. tabularcolumns:: |p{13ex}|L|
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============== ========================================================
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Option Description
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============== ========================================================
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video_nr video device to register (0=/dev/video0, etc)
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range -1 to 64. default is -1 (first available)
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If you have more than 1 camera, this MUST be -1.
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buffer_size Size for each frame buffer in bytes (default 68k)
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num_buffers Number of frame buffers (1-32, default 3)
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alternate USB Alternate (2-7, default 7)
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flicker_freq Frequency for flicker reduction(50 or 60, default 60)
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flicker_mode 0 to disable, or 1 to enable flicker reduction.
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(default 0). This is only effective if the camera
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uses a stv0672 coprocessor.
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============== ========================================================
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Setting the options
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~~~~~~~~~~~~~~~~~~~
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If you are using modules, edit /etc/modules.conf and add an options
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line like this::
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options cpia2 num_buffers=3 buffer_size=65535
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If the driver is compiled into the kernel, at boot time specify them
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like this::
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cpia2.num_buffers=3 cpia2.buffer_size=65535
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What buffer size should I use?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The maximum image size depends on the alternate you choose, and the
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frame rate achieved by the camera. If the compression engine is able to
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keep up with the frame rate, the maximum image size is given by the table
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below.
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The compression engine starts out at maximum compression, and will
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increase image quality until it is close to the size in the table. As long
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as the compression engine can keep up with the frame rate, after a short time
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the images will all be about the size in the table, regardless of resolution.
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At low alternate settings, the compression engine may not be able to
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compress the image enough and will reduce the frame rate by producing larger
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images.
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The default of 68k should be good for most users. This will handle
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any alternate at frame rates down to 15fps. For lower frame rates, it may
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be necessary to increase the buffer size to avoid having frames dropped due
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to insufficient space.
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========== ========== ======== =====
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Alternate bytes/ms 15fps 30fps
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========== ========== ======== =====
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2 128 8533 4267
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3 384 25600 12800
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4 640 42667 21333
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5 768 51200 25600
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6 896 59733 29867
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7 1023 68200 34100
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========== ========== ======== =====
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Table: Image size(bytes)
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How many buffers should I use?
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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For normal streaming, 3 should give the best results. With only 2,
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it is possible for the camera to finish sending one image just after a
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program has started reading the other. If this happens, the driver must drop
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a frame. The exception to this is if you have a heavily loaded machine. In
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this case use 2 buffers. You are probably not reading at the full frame rate.
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If the camera can send multiple images before a read finishes, it could
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overwrite the third buffer before the read finishes, leading to a corrupt
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image. Single and double buffering have extra checks to avoid overwriting.
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Using the camera
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~~~~~~~~~~~~~~~~
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We are providing a modified gqcam application to view the output. In
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order to avoid confusion, here it is called mview. There is also the qx5view
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program which can also control the lights on the qx5 microscope. MJPEG Tools
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(http://mjpeg.sourceforge.net) can also be used to record from the camera.
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