amlogic-aml8726-mx-kernel/Documentation/video4linux/et61x251.txt

		       ET61X[12]51 PC Camera Controllers
				Driver for Linux
		       =================================

			       - Documentation -


Index
=====
1.  Copyright
2.  Disclaimer
3.  License
4.  Overview and features
5.  Module dependencies
6.  Module loading
7.  Module parameters
8.  Optional device control through "sysfs"
9.  Supported devices
10. Notes for V4L2 application developers
11. Contact information


1. Copyright
============
Copyright (C) 2006-2007 by Luca Risolia <luca.risolia@studio.unibo.it>


2. Disclaimer
=============
Etoms is a trademark of Etoms Electronics Corp.
This software is not developed or sponsored by Etoms Electronics.


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 supports the video interface of the devices mounting the ET61X151
or ET61X251 PC Camera Controllers.

It's worth to note that Etoms Electronics has never collaborated with the
author during the development of this project; despite several requests,
Etoms Electronics also refused to release enough detailed specifications of
the video compression engine.

The driver relies on the Video4Linux2 and USB core modules. It has been
designed to run properly on SMP systems as well.

The latest version of the ET61X[12]51 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 and 2 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"
  paragraph);
- full support for the capabilities of every possible image sensors that can
  be connected to the ET61X[12]51 bridges, including, for instance, red, green,
  blue and global gain adjustments and exposure control (see "Supported
  devices" paragraph for details);
- use of default color settings for sunlight conditions;
- dynamic I/O interface for both ET61X[12]51 and image sensor control (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
  the system supports hotplugging;
- no known bugs.


5. Module dependencies
======================
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

To enable advanced debugging functionality on the device through /sysfs:

	# Multimedia devices
	#
	CONFIG_VIDEO_ADV_DEBUG=y

	# 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

And finally:

	# USB Multimedia devices
	#
	CONFIG_USB_ET61X251=m


6. Module loading
=================
To use the driver, it is necessary to load the "et61x251" module into memory
after every other module required: "videodev", "v4l2_common", "compat_ioctl32",
"usbcore" and, depending on the USB host controller you have, "ehci-hcd",
"uhci-hcd" or "ohci-hcd".

Loading can be done as shown below:

	[root@localhost home]# modprobe et61x251

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:           short 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
		registered 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:           frame_timeout
Type:           uint array (min = 0, max = 64)
Syntax:         <n[,...]>
Description:    Timeout for a video frame in seconds. This parameter is
		specific for each detected camera. This parameter can be
		changed at runtime thanks to the /sys filesystem interface.
Default:        2
-------------------------------------------------------------------------------
Name:           debug
Type:           ushort
Syntax:         <n>
Description:    Debugging information level, from 0 to 3:
		0 = none (use carefully)
		1 = critical errors
		2 = significant information
		3 = more verbose messages
		Level 3 is useful for testing only, when only one device
		is used at the same time. It also shows some more information
		about the hardware being detected. This module parameter can be
		changed at runtime thanks to the /sys filesystem interface.
Default:        2
-------------------------------------------------------------------------------


8. Optional device control through "sysfs"
==========================================
If the kernel has been compiled with the CONFIG_VIDEO_ADV_DEBUG option enabled,
it is possible to read and write both the ET61X[12]51 and the image sensor
registers by using the "sysfs" filesystem interface.

There are four files in the /sys/class/video4linux/videoX directory for each
registered camera: "reg", "val", "i2c_reg" and "i2c_val". The first two files
control the ET61X[12]51 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, unless you know what you
are doing. 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
	[root@localhost #] cat i2c_val

Note that if the sensor registers cannot be read, "cat" will fail.
To avoid race conditions, all the I/O accesses to the files are serialized.


9. Supported devices
====================
None of the names of the companies as well as their products will be mentioned
here. They have never collaborated with the author, so no advertising.

From the point of view of a driver, what unambiguously identify a device are
its vendor and product USB identifiers. Below is a list of known identifiers of
devices mounting the ET61X[12]51 PC camera controllers:

Vendor ID  Product ID
---------  ----------
0x102c     0x6151
0x102c     0x6251
0x102c     0x6253
0x102c     0x6254
0x102c     0x6255
0x102c     0x6256
0x102c     0x6257
0x102c     0x6258
0x102c     0x6259
0x102c     0x625a
0x102c     0x625b
0x102c     0x625c
0x102c     0x625d
0x102c     0x625e
0x102c     0x625f
0x102c     0x6260
0x102c     0x6261
0x102c     0x6262
0x102c     0x6263
0x102c     0x6264
0x102c     0x6265
0x102c     0x6266
0x102c     0x6267
0x102c     0x6268
0x102c     0x6269

The following image sensors are supported:

Model       Manufacturer
-----       ------------
TAS5130D1B  Taiwan Advanced Sensor Corporation

All the available control settings of each image sensor are supported through
the V4L2 interface.


10. Notes for V4L2 application developers
=========================================
This driver follows the V4L2 API specifications. In particular, it enforces two
rules:

- exactly one I/O method, either "mmap" or "read", is associated with each
file descriptor. Once it is selected, the application must close and reopen the
device to switch to the other I/O method;

- although it is not mandatory, previously mapped buffer memory should always
be unmapped before calling any "VIDIOC_S_CROP" or "VIDIOC_S_FMT" ioctl's.
The same number of buffers as before will be allocated again to match the size
of the new video frames, so you have to map the buffers again before any I/O
attempts on them.

Consistently with the hardware limits, this driver also supports image
downscaling with arbitrary scaling factors from 1 and 2 in both directions.
However, the V4L2 API specifications don't correctly define how the scaling
factor can be chosen arbitrarily by the "negotiation" of the "source" and
"target" rectangles. To work around this flaw, we have added the convention
that, during the negotiation, whenever the "VIDIOC_S_CROP" ioctl is issued, the
scaling factor is restored to 1.

This driver supports two different video formats: the first one is the "8-bit
Sequential Bayer" format and can be used to obtain uncompressed video data
from the device through the current I/O method, while the second one provides
"raw" compressed video data (without frame headers not related to the
compressed data). The current compression quality may vary from 0 to 1 and can
be selected or queried thanks to the VIDIOC_S_JPEGCOMP and VIDIOC_G_JPEGCOMP
V4L2 ioctl's.


11. Contact information
=======================
The author may be contacted by e-mail at <luca.risolia@studio.unibo.it>.

GPG/PGP encrypted e-mail's are accepted. The GPG key ID of the author is
'FCE635A4'; the public 1024-bit key should be available at any keyserver;
the fingerprint is: '88E8 F32F 7244 68BA 3958  5D40 99DA 5D2A FCE6 35A4'.