sn9c102.txt

linux下sn9c102芯片的数码相机的驱动程序。

	[root@localhost #] cat i2c_val

Note that "cat" will fail if sensor registers cannot be read.

Now let's set the green gain's register of the SN9C101 or SN9C102 chips to 2:

	[root@localhost #] echo 0x11 > reg
	[root@localhost #] echo 2 > val

Note that the SN9C10x always returns 0 when some of its registers are read.
To avoid race conditions, all the I/O accesses to the above files are
serialized.

The sysfs interface also provides the "frame_header" entry, which exports the
frame header of the most recent requested and captured video frame. The header
is 12-bytes long and is appended to every video frame by the SN9C10x
controllers. As an example, this additional information can be used by the user
application for implementing auto-exposure features via software. 

The following table describes the frame header:

Byte #  Value         Description
------  -----         -----------
0x00    0xFF          Frame synchronisation pattern.
0x01    0xFF          Frame synchronisation pattern.
0x02    0x00          Frame synchronisation pattern.
0x03    0xC4          Frame synchronisation pattern.
0x04    0xC4          Frame synchronisation pattern.
0x05    0x96          Frame synchronisation pattern.
0x06    0x00 or 0x01  Unknown meaning. The exact value depends on the chip.
0x07    0xXX          Variable value, whose bits are ff00uzzc, where ff is a
                      frame counter, u is unknown, zz is a size indicator
                      (00 = VGA, 01 = SIF, 10 = QSIF) and c stands for
                      "compression enabled" (1 = yes, 0 = no).
0x08    0xXX          Brightness sum inside Auto-Exposure area (low-byte).
0x09    0xXX          Brightness sum inside Auto-Exposure area (high-byte).
                      For a pure white image, this number will be equal to 500
                      times the area of the specified AE area. For images
                      that are not pure white, the value scales down according
                      to relative whiteness.
0x0A    0xXX          Brightness sum outside Auto-Exposure area (low-byte).
0x0B    0xXX          Brightness sum outside Auto-Exposure area (high-byte).
                      For a pure white image, this number will be equal to 125
                      times the area outside of the specified AE area. For
                      images that are not pure white, the value scales down
                      according to relative whiteness.

The AE area (sx, sy, ex, ey) in the active window can be set by programming the
registers 0x1c, 0x1d, 0x1e and 0x1f of the SN9C10x controllers, where one unit
corresponds to 32 pixels.

[1] The frame header has been documented by Bertrik Sikken.


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 SN9C10x PC camera controllers:

Vendor ID  Product ID
---------  ----------
0x0c45     0x6001
0x0c45     0x6005
0x0c45     0x6009
0x0c45     0x600d
0x0c45     0x6024
0x0c45     0x6025
0x0c45     0x6028
0x0c45     0x6029
0x0c45     0x602a
0x0c45     0x602b
0x0c45     0x602c
0x0c45     0x6030
0x0c45     0x6080
0x0c45     0x6082
0x0c45     0x6083
0x0c45     0x6088
0x0c45     0x608a
0x0c45     0x608b
0x0c45     0x608c
0x0c45     0x608e
0x0c45     0x608f
0x0c45     0x60a0
0x0c45     0x60a2
0x0c45     0x60a3
0x0c45     0x60a8
0x0c45     0x60aa
0x0c45     0x60ab
0x0c45     0x60ac
0x0c45     0x60ae
0x0c45     0x60af
0x0c45     0x60b0
0x0c45     0x60b2
0x0c45     0x60b3
0x0c45     0x60b8
0x0c45     0x60ba
0x0c45     0x60bb
0x0c45     0x60bc
0x0c45     0x60be

The list above does not imply that all those devices work with this driver: up
until now only the ones that mount the following image sensors are supported;
kernel messages will always tell you whether this is the case:

Model       Manufacturer
-----       ------------
HV7131D     Hynix Semiconductor, Inc.
MI-0343     Micron Technology, Inc.
PAS106B     PixArt Imaging, Inc.
PAS202BCB   PixArt Imaging, Inc.
TAS5110C1B  Taiwan Advanced Sensor Corporation
TAS5130D1B  Taiwan Advanced Sensor Corporation

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

Donations of new models for further testing and support would be much
appreciated. Non-available hardware will not be supported by the author of this
driver.


10. How to add plug-in's for new image sensors
==============================================
It should be easy to write plug-in's for new sensors by using the small API
that has been created for this purpose, which is present in "sn9c102_sensor.h"
(documentation is included there). As an example, have a look at the code in
"sn9c102_pas106b.c", which uses the mentioned interface.

At the moment, possible unsupported image sensors are: CIS-VF10 (VGA),
OV7620 (VGA), OV7630 (VGA).


11. 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, 2 and 4 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 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. For maximum flexibility, both the default active video format and the
default compression quality depend on how the image sensor being used is
initialized (as described in the documentation of the API for the image sensors
supplied by this driver).


12. Video frame formats [1]
=======================
The SN9C10x PC Camera Controllers can send images in two possible video
formats over the USB: either native "Sequential RGB Bayer" or Huffman
compressed. The latter is used to achieve high frame rates. The current video
format may be selected or queried from the user application by calling the
VIDIOC_S_FMT or VIDIOC_G_FMT ioctl's, as described in the V4L2 API
specifications.

The name "Sequential Bayer" indicates the organization of the red, green and
blue pixels in one video frame. Each pixel is associated with a 8-bit long
value and is disposed in memory according to the pattern shown below:

B[0]   G[1]    B[2]    G[3]    ...   B[m-2]         G[m-1]
G[m]   R[m+1]  G[m+2]  R[m+2]  ...   G[2m-2]        R[2m-1] 
...
...                                  B[(n-1)(m-2)]  G[(n-1)(m-1)]
...                                  G[n(m-2)]      R[n(m-1)]

The above matrix also represents the sequential or progressive read-out mode of
the (n, m) Bayer color filter array used in many CCD/CMOS image sensors.

One compressed video frame consists of a bitstream that encodes for every R, G,
or B pixel the difference between the value of the pixel itself and some
reference pixel value. Pixels are organised in the Bayer pattern and the Bayer
sub-pixels are tracked individually and alternatingly. For example, in the
first line values for the B and G1 pixels are alternatingly encoded, while in
the second line values for the G2 and R pixels are alternatingly encoded.

The pixel reference value is calculated as follows:
- the 4 top left pixels are encoded in raw uncompressed 8-bit format;
- the value in the top two rows is the value of the pixel left of the current
  pixel;
- the value in the left column is the value of the pixel above the current
  pixel;
- for all other pixels, the reference value is the average of the value of the
  pixel on the left and the value of the pixel above the current pixel;
- there is one code in the bitstream that specifies the value of a pixel
  directly (in 4-bit resolution);
- pixel values need to be clamped inside the range [0..255] for proper
  decoding.

The algorithm purely describes the conversion from compressed Bayer code used
in the SN9C10x chips to uncompressed Bayer. Additional steps are required to
convert this to a color image (i.e. a color interpolation algorithm).
 
The following Huffman codes have been found:
0: +0 (relative to reference pixel value) 
100: +4
101: -4?
1110xxxx: set absolute value to xxxx.0000 
1101: +11
1111: -11
11001: +20
110000: -20
110001: ??? - these codes are apparently not used

[1] The Huffman compression algorithm has been reverse-engineered and
    documented by Bertrik Sikken.


13. Contact information
=======================
The author may be contacted by e-mail at <[e-mail]>.

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'.


14. Credits
===========
Many thanks to following persons for their contribute (listed in alphabetical
order):

- Luca Capello for the donation of a webcam;
- Joao Rodrigo Fuzaro, Joao Limirio, Claudio Filho and Caio Begotti for the
  donation of a webcam;
- Carlos Eduardo Medaglia Dyonisio, who added the support for the PAS202BCB
  image sensor;
- Stefano Mozzi, who donated 45 EU;
- Bertrik Sikken, who reverse-engineered and documented the Huffman compression
  algorithm used in the SN9C10x controllers and implemented the first decoder;
- Mizuno Takafumi for the donation of a webcam;
- An "anonymous" donator (who didn't want his name to be revealed) for the
  donation of a webcam.