sn9c102.txt

linux下sn9c102芯片的数码相机的驱动程序。

                         SN9C10x PC Camera Controllers
                                Driver for Linux
                         =============================

                               - Documentation -


Index
=====
1.  Copyright
2.  Disclaimer
3.  License
4.  Overview and features
5.  Driver installation
6.  Module loading
7.  Module parameters
8.  Optional device control through "sysfs"
9.  Supported devices
10. How to add plug-in's for new image sensors
11. Notes for V4L2 application developers
12. Video frame formats
13. Contact information
14. Credits


1. Copyright
============
Copyright (C) 2004-2005 by Luca Risolia <[e-mail]>


2. Disclaimer
=============
SONiX is a trademark of SONiX Technology Company Limited, inc.
This software is not sponsored or developed by SONiX.


3. License
==========
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.


4. Overview and features
========================
This driver attempts to support the video and audio streaming capabilities of
the devices mounting the SONiX SN9C101, SN9C102 and SN9C103 PC Camera
Controllers.

It's worth to note that SONiX has never collaborated with the author during the
development of this project, despite several requests for enough detailed
specifications of the register tables, compression engine and video data format
of the above chips. Nevertheless, these informations are no longer necessary,
becouse all the aspects related to these chips are known and have been
described in detail in this documentation.

The driver relies on the Video4Linux2 and USB core modules of the official and
stable Linux kernels, version 2.6.10 or greater. It has been designed to run 
properly on SMP systems as well.

The latest version of the SN9C10x driver can be found at the following URL:
http://www.linux-projects.org/

Some of the features of the driver are:

- full compliance with the Video4Linux2 API (see also "Notes for V4L2
  application developers" paragraph);
- available mmap or read/poll methods for video streaming through isochronous
  data transfers;
- automatic detection of image sensor;
- support for any window resolutions and optional panning within the maximum
  pixel area of image sensor;
- image downscaling with arbitrary scaling factors from 1, 2 and 4 in both
  directions (see "Notes for V4L2 application developers" paragraph);
- two different video formats for uncompressed or compressed data in low or
  high compression quality (see also "Notes for V4L2 application developers"
  and "Video frame formats" paragraphs);
- full support for the capabilities of many of the possible image sensors that
  can be connected to the SN9C10x bridges, including, for istance, red, green,
  blue and global gain adjustments and exposure (see "Supported devices"
  paragraph for details);
- use of default color settings for sunlight conditions;
- dynamic I/O interface for both SN9C10x and image sensor control and
  monitoring (see "Optional device control through 'sysfs'" paragraph);
- dynamic driver control thanks to various module parameters (see "Module
  parameters" paragraph);
- up to 64 cameras can be handled at the same time; they can be connected and
  disconnected from the host many times without turning off the computer, if
  your system supports hotplugging;
- no known bugs.


5. Driver installation
======================
As noted above, kernel 2.6.10 is the minimum for this driver; for it to work
properly, the driver needs kernel support for Video4Linux and USB.

The following options of the kernel configuration file must be enabled and
corresponding modules must be compiled:

	# Multimedia devices
	#
	CONFIG_VIDEO_DEV=m

	# USB support
	#
	CONFIG_USB=m

In addition, depending on the hardware being used, the modules below are
necessary:

	# USB Host Controller Drivers
	#
	CONFIG_USB_EHCI_HCD=m
	CONFIG_USB_UHCI_HCD=m
	CONFIG_USB_OHCI_HCD=m

Moving along to the SN9C10x driver: after having downloaded the package,
decompress and compile:

	[user@localhost home]$ tar xvzf sn9c102-x.x.tar.gz
	[user@localhost home]$ cd sn9c102-x.x

(where "x.x" has to be substituted with the right version of the module just
downloaded)

It is necessary to properly configure your particular kernel source tree before
compiling the driver. The modular building process is used; therefore you must
have read and write access to your kernel source tree. If not, log in as root
before running the following commands:

	[user@localhost sn9c102-x.x]$ make clean
	[user@localhost sn9c102-x.x]$ make modules

If the commands fail, control the Makefile and change the path to the kernel
source tree or to any other files, according to your system configuration;
then run the previous commands again.

If everything went well, the SN9C10x driver can be used either immediatly
(skip to the next paragraph) or be installed.

The driver will be installed in the default directory reserved for modules
being built outside the kernel. This means that the possible version of the
driver present in the official Linux kernel tree will not be overwritten during
the installation process.

To install the driver, run as root:

	[root@localhost sn9c102-x.x]# make modules_install


6. Module loading
=================
To use the driver, it is necessary to load the "sn9c102" module into memory
after every other module required: "videodev", "usbcore" and, depending on
the USB host controller you have, "ehci-hcd", "uhci-hcd" or "ohci-hcd".

Loading can be done as shown below.

If the SN9C10x driver has been installed as shown in the previous paragraph:

	[root@localhost home]# modprobe sn9c102

otherwise, if you have not installed the driver, but have just compiled it,
run "insmod" indicating the path to the module; for example:

	[root@localhost sn9c102-x.x]# insmod ./sn9c102.ko

At this point the devices should be recognized. You can invoke "dmesg" to
analyze kernel messages and verify that the loading process has gone well:

	[user@localhost home]$ dmesg


7. Module parameters
====================
Module parameters are listed below:
-------------------------------------------------------------------------------
Name:           video_nr
Type:           int array (min = 0, max = 64)
Syntax:         <-1|n[,...]> 
Description:    Specify V4L2 minor mode number:
                -1 = use next available
                 n = use minor number n
                You can specify up to 64 cameras this way.
                For example:
                video_nr=-1,2,-1 would assign minor number 2 to the second
                recognized camera and use auto for the first one and for every
                other camera.
Default:        -1
-------------------------------------------------------------------------------
Name:           force_munmap;
Type:           bool array (min = 0, max = 64)
Syntax:         <0|1[,...]> 
Description:    Force the application to unmap previously mapped buffer memory
                before calling any VIDIOC_S_CROP or VIDIOC_S_FMT ioctl's. Not
                all the applications support this feature. This parameter is
                specific for each detected camera.
                0 = do not force memory unmapping"
                1 = force memory unmapping (save memory)"
Default:        0
-------------------------------------------------------------------------------
Name:           debug
Type:           int
Syntax:         <n> 
Description:    Debugging information level, from 0 to 3:
                0 = none (use carefully)
                1 = critical errors
                2 = significant informations
                3 = more verbose messages
                Level 3 is useful for testing only, when only one device
                is used. It also shows some more informations about the
                hardware being detected. This parameter can be changed at
                runtime thanks to the /sys filesystem.
Default:        2
-------------------------------------------------------------------------------


8. Optional device control through "sysfs" [1]
==========================================
It is possible to read and write both the SN9C10x and the image sensor
registers by using the "sysfs" filesystem interface.

Every time a supported device is recognized, a write-only file named "green" is
created in the /sys/class/video4linux/videoX directory. You can set the green
channel's gain by writing the desired value to it. The value may range from 0
to 15 for SN9C101 or SN9C102 bridges, from 0 to 127 for SN9C103 bridges.
Similarly, only for SN9C103 controllers, blue and red gain control files are
available in the same directory, for which accepted values may range from 0 to
127.

There are other four entries in the directory above for each registered camera:
"reg", "val", "i2c_reg" and "i2c_val". The first two files control the
SN9C10x bridge, while the other two control the sensor chip. "reg" and
"i2c_reg" hold the values of the current register index where the following
reading/writing operations are addressed at through "val" and "i2c_val". Their
use is not intended for end-users. Note that "i2c_reg" and "i2c_val" will not
be created if the sensor does not actually support the standard I2C protocol or
its registers are not 8-bit long. Also, remember that you must be logged in as
root before writing to them.

As an example, suppose we were to want to read the value contained in the
register number 1 of the sensor register table - which is usually the product
identifier - of the camera registered as "/dev/video0":

	[root@localhost #] cd /sys/class/video4linux/video0
	[root@localhost #] echo 1 > i2c_reg