blob: b26f5195af51f58db1d4a04f2826e044b29bc8a2 [file] [log] [blame]
Linus Torvalds1da177e2005-04-16 15:20:36 -07001
Luca Risoliaf327ebb2007-01-08 10:43:56 -03002 SN9C1xx PC Camera Controllers
Michael Krufky6e204092006-05-23 17:41:31 -03003 Driver for Linux
4 =============================
Linus Torvalds1da177e2005-04-16 15:20:36 -07005
Michael Krufky6e204092006-05-23 17:41:31 -03006 - Documentation -
Linus Torvalds1da177e2005-04-16 15:20:36 -07007
8
9Index
10=====
111. Copyright
122. Disclaimer
133. License
144. Overview and features
155. Module dependencies
166. Module loading
177. Module parameters
188. Optional device control through "sysfs"
199. Supported devices
Luca Risoliaa966f3e2006-01-05 18:14:04 +00002010. Notes for V4L2 application developers
2111. Video frame formats
2212. Contact information
2313. Credits
Linus Torvalds1da177e2005-04-16 15:20:36 -070024
25
261. Copyright
27============
Luca Risoliaf423b9a2007-03-26 16:12:04 -030028Copyright (C) 2004-2007 by Luca Risolia <luca.risolia@studio.unibo.it>
Linus Torvalds1da177e2005-04-16 15:20:36 -070029
30
312. Disclaimer
32=============
33SONiX is a trademark of SONiX Technology Company Limited, inc.
34This software is not sponsored or developed by SONiX.
35
36
373. License
38==========
39This program is free software; you can redistribute it and/or modify
40it under the terms of the GNU General Public License as published by
41the Free Software Foundation; either version 2 of the License, or
42(at your option) any later version.
43
44This program is distributed in the hope that it will be useful,
45but WITHOUT ANY WARRANTY; without even the implied warranty of
46MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
47GNU General Public License for more details.
48
49You should have received a copy of the GNU General Public License
50along with this program; if not, write to the Free Software
51Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
52
53
544. Overview and features
55========================
Luca Risoliaf327ebb2007-01-08 10:43:56 -030056This driver attempts to support the video interface of the devices assembling
57the SONiX SN9C101, SN9C102, SN9C103, SN9C105 and SN9C120 PC Camera Controllers
58("SN9C1xx" from now on).
Linus Torvalds1da177e2005-04-16 15:20:36 -070059
60The driver relies on the Video4Linux2 and USB core modules. It has been
61designed to run properly on SMP systems as well.
62
Luca Risoliaf327ebb2007-01-08 10:43:56 -030063The latest version of the SN9C1xx driver can be found at the following URL:
Linus Torvalds1da177e2005-04-16 15:20:36 -070064http://www.linux-projects.org/
65
66Some of the features of the driver are:
67
68- full compliance with the Video4Linux2 API (see also "Notes for V4L2
69 application developers" paragraph);
70- available mmap or read/poll methods for video streaming through isochronous
71 data transfers;
72- automatic detection of image sensor;
Luca Risoliaa966f3e2006-01-05 18:14:04 +000073- support for built-in microphone interface;
Linus Torvalds1da177e2005-04-16 15:20:36 -070074- support for any window resolutions and optional panning within the maximum
75 pixel area of image sensor;
76- image downscaling with arbitrary scaling factors from 1, 2 and 4 in both
77 directions (see "Notes for V4L2 application developers" paragraph);
78- two different video formats for uncompressed or compressed data in low or
79 high compression quality (see also "Notes for V4L2 application developers"
80 and "Video frame formats" paragraphs);
81- full support for the capabilities of many of the possible image sensors that
Luca Risoliaf327ebb2007-01-08 10:43:56 -030082 can be connected to the SN9C1xx bridges, including, for instance, red, green,
Linus Torvalds1da177e2005-04-16 15:20:36 -070083 blue and global gain adjustments and exposure (see "Supported devices"
84 paragraph for details);
85- use of default color settings for sunlight conditions;
Luca Risoliaf327ebb2007-01-08 10:43:56 -030086- dynamic I/O interface for both SN9C1xx and image sensor control and
Linus Torvalds1da177e2005-04-16 15:20:36 -070087 monitoring (see "Optional device control through 'sysfs'" paragraph);
88- dynamic driver control thanks to various module parameters (see "Module
89 parameters" paragraph);
90- up to 64 cameras can be handled at the same time; they can be connected and
91 disconnected from the host many times without turning off the computer, if
Luca Risoliaa966f3e2006-01-05 18:14:04 +000092 the system supports hotplugging;
Linus Torvalds1da177e2005-04-16 15:20:36 -070093- no known bugs.
94
95
965. Module dependencies
97======================
98For it to work properly, the driver needs kernel support for Video4Linux and
99USB.
100
101The following options of the kernel configuration file must be enabled and
102corresponding modules must be compiled:
103
104 # Multimedia devices
105 #
106 CONFIG_VIDEO_DEV=m
107
Luca Risoliacd6fcc52006-01-13 17:19:43 +0000108To enable advanced debugging functionality on the device through /sysfs:
109
110 # Multimedia devices
111 #
112 CONFIG_VIDEO_ADV_DEBUG=y
113
Linus Torvalds1da177e2005-04-16 15:20:36 -0700114 # USB support
115 #
116 CONFIG_USB=m
117
118In addition, depending on the hardware being used, the modules below are
119necessary:
120
121 # USB Host Controller Drivers
122 #
123 CONFIG_USB_EHCI_HCD=m
124 CONFIG_USB_UHCI_HCD=m
125 CONFIG_USB_OHCI_HCD=m
126
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300127The SN9C103, SN9c105 and SN9C120 controllers also provide a built-in microphone
128interface. It is supported by the USB Audio driver thanks to the ALSA API:
Luca Risoliaa966f3e2006-01-05 18:14:04 +0000129
130 # Sound
131 #
132 CONFIG_SOUND=y
133
134 # Advanced Linux Sound Architecture
135 #
136 CONFIG_SND=m
137
138 # USB devices
139 #
140 CONFIG_SND_USB_AUDIO=m
141
Linus Torvalds1da177e2005-04-16 15:20:36 -0700142And finally:
143
144 # USB Multimedia devices
145 #
146 CONFIG_USB_SN9C102=m
147
148
1496. Module loading
150=================
151To use the driver, it is necessary to load the "sn9c102" module into memory
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300152after every other module required: "videodev", "v4l2_common", "compat_ioctl32",
153"usbcore" and, depending on the USB host controller you have, "ehci-hcd",
154"uhci-hcd" or "ohci-hcd".
Linus Torvalds1da177e2005-04-16 15:20:36 -0700155
156Loading can be done as shown below:
157
158 [root@localhost home]# modprobe sn9c102
159
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300160Note that the module is called "sn9c102" for historic reasons, althought it
161does not just support the SN9C102.
162
163At this point all the devices supported by the driver and connected to the USB
164ports should be recognized. You can invoke "dmesg" to analyze kernel messages
165and verify that the loading process has gone well:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700166
167 [user@localhost home]$ dmesg
168
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300169or, to isolate all the kernel messages generated by the driver:
170
171 [user@localhost home]$ dmesg | grep sn9c102
172
Linus Torvalds1da177e2005-04-16 15:20:36 -0700173
1747. Module parameters
175====================
176Module parameters are listed below:
177-------------------------------------------------------------------------------
178Name: video_nr
Luca Risoliaa966f3e2006-01-05 18:14:04 +0000179Type: short array (min = 0, max = 64)
Michael Krufky1864cfb2006-04-02 03:14:11 -0300180Syntax: <-1|n[,...]>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700181Description: Specify V4L2 minor mode number:
Michael Krufky6e204092006-05-23 17:41:31 -0300182 -1 = use next available
183 n = use minor number n
184 You can specify up to 64 cameras this way.
185 For example:
186 video_nr=-1,2,-1 would assign minor number 2 to the second
187 recognized camera and use auto for the first one and for every
188 other camera.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700189Default: -1
190-------------------------------------------------------------------------------
Luca Risoliaa966f3e2006-01-05 18:14:04 +0000191Name: force_munmap
Linus Torvalds1da177e2005-04-16 15:20:36 -0700192Type: bool array (min = 0, max = 64)
Michael Krufky1864cfb2006-04-02 03:14:11 -0300193Syntax: <0|1[,...]>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700194Description: Force the application to unmap previously mapped buffer memory
Michael Krufky6e204092006-05-23 17:41:31 -0300195 before calling any VIDIOC_S_CROP or VIDIOC_S_FMT ioctl's. Not
196 all the applications support this feature. This parameter is
197 specific for each detected camera.
198 0 = do not force memory unmapping
199 1 = force memory unmapping (save memory)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700200Default: 0
201-------------------------------------------------------------------------------
Luca Risolia2ffab022006-02-25 06:50:47 +0000202Name: frame_timeout
203Type: uint array (min = 0, max = 64)
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300204Syntax: <0|n[,...]>
205Description: Timeout for a video frame in seconds before returning an I/O
206 error; 0 for infinity. This parameter is specific for each
207 detected camera and can be changed at runtime thanks to the
208 /sys filesystem interface.
Luca Risolia2ffab022006-02-25 06:50:47 +0000209Default: 2
210-------------------------------------------------------------------------------
Linus Torvalds1da177e2005-04-16 15:20:36 -0700211Name: debug
Luca Risoliaa966f3e2006-01-05 18:14:04 +0000212Type: ushort
Michael Krufky1864cfb2006-04-02 03:14:11 -0300213Syntax: <n>
Linus Torvalds1da177e2005-04-16 15:20:36 -0700214Description: Debugging information level, from 0 to 3:
Michael Krufky6e204092006-05-23 17:41:31 -0300215 0 = none (use carefully)
216 1 = critical errors
217 2 = significant informations
218 3 = more verbose messages
Luca Risoliaf423b9a2007-03-26 16:12:04 -0300219 Level 3 is useful for testing only. It also shows some more
220 informations about the hardware being detected.
221 This parameter can be changed at runtime thanks to the /sys
222 filesystem interface.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700223Default: 2
224-------------------------------------------------------------------------------
225
226
2278. Optional device control through "sysfs" [1]
228==========================================
Luca Risoliacd6fcc52006-01-13 17:19:43 +0000229If the kernel has been compiled with the CONFIG_VIDEO_ADV_DEBUG option enabled,
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300230it is possible to read and write both the SN9C1xx and the image sensor
Linus Torvalds1da177e2005-04-16 15:20:36 -0700231registers by using the "sysfs" filesystem interface.
232
233Every time a supported device is recognized, a write-only file named "green" is
234created in the /sys/class/video4linux/videoX directory. You can set the green
235channel's gain by writing the desired value to it. The value may range from 0
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300236to 15 for the SN9C101 or SN9C102 bridges, from 0 to 127 for the SN9C103,
237SN9C105 and SN9C120 bridges.
Luca Risoliaf423b9a2007-03-26 16:12:04 -0300238Similarly, only for the SN9C103, SN9C105 and SN9C120 controllers, blue and red
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300239gain control files are available in the same directory, for which accepted
240values may range from 0 to 127.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700241
242There are other four entries in the directory above for each registered camera:
243"reg", "val", "i2c_reg" and "i2c_val". The first two files control the
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300244SN9C1xx bridge, while the other two control the sensor chip. "reg" and
Linus Torvalds1da177e2005-04-16 15:20:36 -0700245"i2c_reg" hold the values of the current register index where the following
246reading/writing operations are addressed at through "val" and "i2c_val". Their
247use is not intended for end-users. Note that "i2c_reg" and "i2c_val" will not
248be created if the sensor does not actually support the standard I2C protocol or
249its registers are not 8-bit long. Also, remember that you must be logged in as
250root before writing to them.
251
252As an example, suppose we were to want to read the value contained in the
253register number 1 of the sensor register table - which is usually the product
254identifier - of the camera registered as "/dev/video0":
255
256 [root@localhost #] cd /sys/class/video4linux/video0
257 [root@localhost #] echo 1 > i2c_reg
258 [root@localhost #] cat i2c_val
259
260Note that "cat" will fail if sensor registers cannot be read.
261
262Now let's set the green gain's register of the SN9C101 or SN9C102 chips to 2:
263
264 [root@localhost #] echo 0x11 > reg
265 [root@localhost #] echo 2 > val
266
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300267Note that the SN9C1xx always returns 0 when some of its registers are read.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700268To avoid race conditions, all the I/O accesses to the above files are
269serialized.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700270The sysfs interface also provides the "frame_header" entry, which exports the
271frame header of the most recent requested and captured video frame. The header
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300272is always 18-bytes long and is appended to every video frame by the SN9C1xx
Linus Torvalds1da177e2005-04-16 15:20:36 -0700273controllers. As an example, this additional information can be used by the user
Michael Krufky1864cfb2006-04-02 03:14:11 -0300274application for implementing auto-exposure features via software.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700275
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300276The following table describes the frame header exported by the SN9C101 and
277SN9C102:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700278
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300279Byte # Value or bits Description
280------ ------------- -----------
2810x00 0xFF Frame synchronisation pattern
2820x01 0xFF Frame synchronisation pattern
2830x02 0x00 Frame synchronisation pattern
2840x03 0xC4 Frame synchronisation pattern
2850x04 0xC4 Frame synchronisation pattern
2860x05 0x96 Frame synchronisation pattern
2870x06 [3:0] Read channel gain control = (1+R_GAIN/8)
288 [7:4] Blue channel gain control = (1+B_GAIN/8)
2890x07 [ 0 ] Compression mode. 0=No compression, 1=Compression enabled
290 [2:1] Maximum scale factor for compression
291 [ 3 ] 1 = USB fifo(2K bytes) is full
292 [ 4 ] 1 = Digital gain is finish
293 [ 5 ] 1 = Exposure is finish
294 [7:6] Frame index
2950x08 [7:0] Y sum inside Auto-Exposure area (low-byte)
2960x09 [7:0] Y sum inside Auto-Exposure area (high-byte)
297 where Y sum = (R/4 + 5G/16 + B/8) / 32
2980x0A [7:0] Y sum outside Auto-Exposure area (low-byte)
2990x0B [7:0] Y sum outside Auto-Exposure area (high-byte)
300 where Y sum = (R/4 + 5G/16 + B/8) / 128
3010x0C 0xXX Not used
3020x0D 0xXX Not used
3030x0E 0xXX Not used
3040x0F 0xXX Not used
3050x10 0xXX Not used
3060x11 0xXX Not used
Luca Risoliaa966f3e2006-01-05 18:14:04 +0000307
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300308The following table describes the frame header exported by the SN9C103:
Luca Risoliaa966f3e2006-01-05 18:14:04 +0000309
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300310Byte # Value or bits Description
311------ ------------- -----------
3120x00 0xFF Frame synchronisation pattern
3130x01 0xFF Frame synchronisation pattern
3140x02 0x00 Frame synchronisation pattern
3150x03 0xC4 Frame synchronisation pattern
3160x04 0xC4 Frame synchronisation pattern
3170x05 0x96 Frame synchronisation pattern
3180x06 [6:0] Read channel gain control = (1/2+R_GAIN/64)
3190x07 [6:0] Blue channel gain control = (1/2+B_GAIN/64)
320 [7:4]
3210x08 [ 0 ] Compression mode. 0=No compression, 1=Compression enabled
322 [2:1] Maximum scale factor for compression
323 [ 3 ] 1 = USB fifo(2K bytes) is full
324 [ 4 ] 1 = Digital gain is finish
325 [ 5 ] 1 = Exposure is finish
326 [7:6] Frame index
3270x09 [7:0] Y sum inside Auto-Exposure area (low-byte)
3280x0A [7:0] Y sum inside Auto-Exposure area (high-byte)
329 where Y sum = (R/4 + 5G/16 + B/8) / 32
3300x0B [7:0] Y sum outside Auto-Exposure area (low-byte)
3310x0C [7:0] Y sum outside Auto-Exposure area (high-byte)
332 where Y sum = (R/4 + 5G/16 + B/8) / 128
3330x0D [1:0] Audio frame number
334 [ 2 ] 1 = Audio is recording
3350x0E [7:0] Audio summation (low-byte)
3360x0F [7:0] Audio summation (high-byte)
3370x10 [7:0] Audio sample count
3380x11 [7:0] Audio peak data in audio frame
Linus Torvalds1da177e2005-04-16 15:20:36 -0700339
340The AE area (sx, sy, ex, ey) in the active window can be set by programming the
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300341registers 0x1c, 0x1d, 0x1e and 0x1f of the SN9C1xx controllers, where one unit
Linus Torvalds1da177e2005-04-16 15:20:36 -0700342corresponds to 32 pixels.
343
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300344[1] The frame headers exported by the SN9C105 and SN9C120 are not described.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700345
346
3479. Supported devices
348====================
349None of the names of the companies as well as their products will be mentioned
350here. They have never collaborated with the author, so no advertising.
351
352From the point of view of a driver, what unambiguously identify a device are
353its vendor and product USB identifiers. Below is a list of known identifiers of
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300354devices assembling the SN9C1xx PC camera controllers:
Linus Torvalds1da177e2005-04-16 15:20:36 -0700355
356Vendor ID Product ID
357--------- ----------
Luca Risolia480b55c22007-05-02 10:04:03 -03003580x0458 0x7025
3590x045e 0x00f5
3600x045e 0x00f7
Luca Risoliaf327ebb2007-01-08 10:43:56 -03003610x0471 0x0327
3620x0471 0x0328
Linus Torvalds1da177e2005-04-16 15:20:36 -07003630x0c45 0x6001
3640x0c45 0x6005
Luca Risolia2ffab022006-02-25 06:50:47 +00003650x0c45 0x6007
Linus Torvalds1da177e2005-04-16 15:20:36 -07003660x0c45 0x6009
3670x0c45 0x600d
Luca Risoliaf327ebb2007-01-08 10:43:56 -03003680x0c45 0x6011
3690x0c45 0x6019
Linus Torvalds1da177e2005-04-16 15:20:36 -07003700x0c45 0x6024
3710x0c45 0x6025
3720x0c45 0x6028
3730x0c45 0x6029
3740x0c45 0x602a
3750x0c45 0x602b
3760x0c45 0x602c
Luca Risoliab9df9782005-06-25 16:30:24 +02003770x0c45 0x602d
Luca Risoliaa966f3e2006-01-05 18:14:04 +00003780x0c45 0x602e
Linus Torvalds1da177e2005-04-16 15:20:36 -07003790x0c45 0x6030
Luca Risoliaf327ebb2007-01-08 10:43:56 -03003800x0c45 0x603f
Linus Torvalds1da177e2005-04-16 15:20:36 -07003810x0c45 0x6080
3820x0c45 0x6082
3830x0c45 0x6083
3840x0c45 0x6088
3850x0c45 0x608a
3860x0c45 0x608b
3870x0c45 0x608c
3880x0c45 0x608e
3890x0c45 0x608f
3900x0c45 0x60a0
3910x0c45 0x60a2
3920x0c45 0x60a3
3930x0c45 0x60a8
3940x0c45 0x60aa
3950x0c45 0x60ab
3960x0c45 0x60ac
3970x0c45 0x60ae
3980x0c45 0x60af
3990x0c45 0x60b0
4000x0c45 0x60b2
4010x0c45 0x60b3
4020x0c45 0x60b8
4030x0c45 0x60ba
4040x0c45 0x60bb
4050x0c45 0x60bc
4060x0c45 0x60be
Luca Risoliaf327ebb2007-01-08 10:43:56 -03004070x0c45 0x60c0
Luca Risoliaf423b9a2007-03-26 16:12:04 -03004080x0c45 0x60c2
Luca Risoliaf327ebb2007-01-08 10:43:56 -03004090x0c45 0x60c8
4100x0c45 0x60cc
4110x0c45 0x60ea
4120x0c45 0x60ec
Luca Risoliaf423b9a2007-03-26 16:12:04 -03004130x0c45 0x60ef
Luca Risoliaf327ebb2007-01-08 10:43:56 -03004140x0c45 0x60fa
4150x0c45 0x60fb
4160x0c45 0x60fc
4170x0c45 0x60fe
Luca Risoliaf423b9a2007-03-26 16:12:04 -03004180x0c45 0x6102
4190x0c45 0x6108
4200x0c45 0x610f
Luca Risoliaf327ebb2007-01-08 10:43:56 -03004210x0c45 0x6130
Luca Risoliaf423b9a2007-03-26 16:12:04 -03004220x0c45 0x6138
Luca Risoliaf327ebb2007-01-08 10:43:56 -03004230x0c45 0x613a
4240x0c45 0x613b
4250x0c45 0x613c
4260x0c45 0x613e
Linus Torvalds1da177e2005-04-16 15:20:36 -0700427
428The list above does not imply that all those devices work with this driver: up
Luca Risoliaf423b9a2007-03-26 16:12:04 -0300429until now only the ones that assemble the following pairs of SN9C1xx bridges
430and image sensors are supported; kernel messages will always tell you whether
431this is the case (see "Module loading" paragraph):
Linus Torvalds1da177e2005-04-16 15:20:36 -0700432
Luca Risoliaf423b9a2007-03-26 16:12:04 -0300433Image sensor / SN9C1xx bridge | SN9C10[12] SN9C103 SN9C105 SN9C120
434-------------------------------------------------------------------------------
435HV7131D Hynix Semiconductor | Yes No No No
436HV7131R Hynix Semiconductor | No Yes Yes Yes
437MI-0343 Micron Technology | Yes No No No
Luca Risolia480b55c22007-05-02 10:04:03 -0300438MI-0360 Micron Technology | No Yes Yes Yes
Luca Risolia3770be32007-06-13 14:37:50 -0300439OV7630 OmniVision Technologies | Yes Yes Yes Yes
Luca Risoliaf423b9a2007-03-26 16:12:04 -0300440OV7660 OmniVision Technologies | No No Yes Yes
441PAS106B PixArt Imaging | Yes No No No
442PAS202B PixArt Imaging | Yes Yes No No
443TAS5110C1B Taiwan Advanced Sensor | Yes No No No
444TAS5110D Taiwan Advanced Sensor | Yes No No No
445TAS5130D1B Taiwan Advanced Sensor | Yes No No No
Linus Torvalds1da177e2005-04-16 15:20:36 -0700446
Luca Risoliaf423b9a2007-03-26 16:12:04 -0300447"Yes" means that the pair is supported by the driver, while "No" means that the
448pair does not exist or is not supported by the driver.
449
450Only some of the available control settings of each image sensor are supported
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300451through the V4L2 interface.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700452
453Donations of new models for further testing and support would be much
454appreciated. Non-available hardware will not be supported by the author of this
455driver.
456
457
Luca Risoliaa966f3e2006-01-05 18:14:04 +000045810. Notes for V4L2 application developers
Linus Torvalds1da177e2005-04-16 15:20:36 -0700459=========================================
460This driver follows the V4L2 API specifications. In particular, it enforces two
461rules:
462
463- exactly one I/O method, either "mmap" or "read", is associated with each
464file descriptor. Once it is selected, the application must close and reopen the
465device to switch to the other I/O method;
466
467- although it is not mandatory, previously mapped buffer memory should always
468be unmapped before calling any "VIDIOC_S_CROP" or "VIDIOC_S_FMT" ioctl's.
469The same number of buffers as before will be allocated again to match the size
470of the new video frames, so you have to map the buffers again before any I/O
471attempts on them.
472
473Consistently with the hardware limits, this driver also supports image
474downscaling with arbitrary scaling factors from 1, 2 and 4 in both directions.
475However, the V4L2 API specifications don't correctly define how the scaling
476factor can be chosen arbitrarily by the "negotiation" of the "source" and
477"target" rectangles. To work around this flaw, we have added the convention
478that, during the negotiation, whenever the "VIDIOC_S_CROP" ioctl is issued, the
479scaling factor is restored to 1.
480
481This driver supports two different video formats: the first one is the "8-bit
482Sequential Bayer" format and can be used to obtain uncompressed video data
483from the device through the current I/O method, while the second one provides
Luca Risolia480b55c22007-05-02 10:04:03 -0300484either "raw" compressed video data (without frame headers not related to the
485compressed data) or standard JPEG (with frame headers). The compression quality
486may vary from 0 to 1 and can be selected or queried thanks to the
487VIDIOC_S_JPEGCOMP and VIDIOC_G_JPEGCOMP V4L2 ioctl's. For maximum flexibility,
488both the default active video format and the default compression quality
489depend on how the image sensor being used is initialized.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700490
491
Luca Risoliaa966f3e2006-01-05 18:14:04 +000049211. Video frame formats [1]
Linus Torvalds1da177e2005-04-16 15:20:36 -0700493=======================
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300494The SN9C1xx PC Camera Controllers can send images in two possible video
495formats over the USB: either native "Sequential RGB Bayer" or compressed.
496The compression is used to achieve high frame rates. With regard to the
497SN9C101, SN9C102 and SN9C103, the compression is based on the Huffman encoding
Luca Risoliaf423b9a2007-03-26 16:12:04 -0300498algorithm described below, while with regard to the SN9C105 and SN9C120 the
499compression is based on the JPEG standard.
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300500The current video format may be selected or queried from the user application
501by calling the VIDIOC_S_FMT or VIDIOC_G_FMT ioctl's, as described in the V4L2
502API specifications.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700503
504The name "Sequential Bayer" indicates the organization of the red, green and
505blue pixels in one video frame. Each pixel is associated with a 8-bit long
506value and is disposed in memory according to the pattern shown below:
507
508B[0] G[1] B[2] G[3] ... B[m-2] G[m-1]
Michael Krufky1864cfb2006-04-02 03:14:11 -0300509G[m] R[m+1] G[m+2] R[m+2] ... G[2m-2] R[2m-1]
Linus Torvalds1da177e2005-04-16 15:20:36 -0700510...
511... B[(n-1)(m-2)] G[(n-1)(m-1)]
512... G[n(m-2)] R[n(m-1)]
513
514The above matrix also represents the sequential or progressive read-out mode of
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300515the (n, m) Bayer color filter array used in many CCD or CMOS image sensors.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700516
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300517The Huffman compressed video frame consists of a bitstream that encodes for
518every R, G, or B pixel the difference between the value of the pixel itself and
519some reference pixel value. Pixels are organised in the Bayer pattern and the
520Bayer sub-pixels are tracked individually and alternatingly. For example, in
521the first line values for the B and G1 pixels are alternatingly encoded, while
522in the second line values for the G2 and R pixels are alternatingly encoded.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700523
524The pixel reference value is calculated as follows:
525- the 4 top left pixels are encoded in raw uncompressed 8-bit format;
526- the value in the top two rows is the value of the pixel left of the current
527 pixel;
528- the value in the left column is the value of the pixel above the current
529 pixel;
530- for all other pixels, the reference value is the average of the value of the
531 pixel on the left and the value of the pixel above the current pixel;
532- there is one code in the bitstream that specifies the value of a pixel
533 directly (in 4-bit resolution);
534- pixel values need to be clamped inside the range [0..255] for proper
535 decoding.
536
537The algorithm purely describes the conversion from compressed Bayer code used
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300538in the SN9C101, SN9C102 and SN9C103 chips to uncompressed Bayer. Additional
539steps are required to convert this to a color image (i.e. a color interpolation
540algorithm).
Michael Krufky1864cfb2006-04-02 03:14:11 -0300541
Linus Torvalds1da177e2005-04-16 15:20:36 -0700542The following Huffman codes have been found:
Michael Krufky1864cfb2006-04-02 03:14:11 -03005430: +0 (relative to reference pixel value)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700544100: +4
545101: -4?
Michael Krufky1864cfb2006-04-02 03:14:11 -03005461110xxxx: set absolute value to xxxx.0000
Linus Torvalds1da177e2005-04-16 15:20:36 -07005471101: +11
5481111: -11
54911001: +20
550110000: -20
551110001: ??? - these codes are apparently not used
552
553[1] The Huffman compression algorithm has been reverse-engineered and
554 documented by Bertrik Sikken.
555
556
Luca Risoliaa966f3e2006-01-05 18:14:04 +000055712. Contact information
Linus Torvalds1da177e2005-04-16 15:20:36 -0700558=======================
559The author may be contacted by e-mail at <luca.risolia@studio.unibo.it>.
560
561GPG/PGP encrypted e-mail's are accepted. The GPG key ID of the author is
562'FCE635A4'; the public 1024-bit key should be available at any keyserver;
563the fingerprint is: '88E8 F32F 7244 68BA 3958 5D40 99DA 5D2A FCE6 35A4'.
564
565
Luca Risoliaa966f3e2006-01-05 18:14:04 +000056613. Credits
Linus Torvalds1da177e2005-04-16 15:20:36 -0700567===========
568Many thanks to following persons for their contribute (listed in alphabetical
569order):
570
Luca Risoliaddef2dc2007-11-12 11:42:54 -0300571- David Anderson for the donation of a webcam;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700572- Luca Capello for the donation of a webcam;
Luca Risolia2ffab022006-02-25 06:50:47 +0000573- Philippe Coval for having helped testing the PAS202BCA image sensor;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700574- Joao Rodrigo Fuzaro, Joao Limirio, Claudio Filho and Caio Begotti for the
575 donation of a webcam;
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300576- Dennis Heitmann for the donation of a webcam;
Luca Risoliab9df9782005-06-25 16:30:24 +0200577- Jon Hollstrom for the donation of a webcam;
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300578- Nick McGill for the donation of a webcam;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700579- Carlos Eduardo Medaglia Dyonisio, who added the support for the PAS202BCB
580 image sensor;
581- Stefano Mozzi, who donated 45 EU;
Luca Risoliab9df9782005-06-25 16:30:24 +0200582- Andrew Pearce for the donation of a webcam;
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300583- John Pullan for the donation of a webcam;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700584- Bertrik Sikken, who reverse-engineered and documented the Huffman compression
Luca Risoliaf327ebb2007-01-08 10:43:56 -0300585 algorithm used in the SN9C101, SN9C102 and SN9C103 controllers and
586 implemented the first decoder;
Luca Risolia3770be32007-06-13 14:37:50 -0300587- Ronny Standke for the donation of a webcam;
Linus Torvalds1da177e2005-04-16 15:20:36 -0700588- Mizuno Takafumi for the donation of a webcam;
Luca Risoliaa966f3e2006-01-05 18:14:04 +0000589- an "anonymous" donator (who didn't want his name to be revealed) for the
Linus Torvalds1da177e2005-04-16 15:20:36 -0700590 donation of a webcam.
Luca Risoliaf423b9a2007-03-26 16:12:04 -0300591- an anonymous donator for the donation of four webcams and two boards with ten
592 image sensors.