SN9C10x 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. 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 <luca.risolia@studio.unibo.it> 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. 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. 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 # 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_SN9C102=m 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: [root@localhost home]# modprobe sn9c102 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 [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 0x602d 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. OV7630 OmniVision Technologies, 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 <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'. 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; - Jon Hollstrom 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; - Andrew Pearce for the donation of a webcam; - 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.