cpia2.rst (5612B)
1.. SPDX-License-Identifier: GPL-2.0 2 3The cpia2 driver 4================ 5 6Authors: Peter Pregler <Peter_Pregler@email.com>, 7Scott J. Bertin <scottbertin@yahoo.com>, and 8Jarl Totland <Jarl.Totland@bdc.no> for the original cpia driver, which 9this one was modelled from. 10 11Introduction 12------------ 13 14This is a driver for STMicroelectronics's CPiA2 (second generation 15Colour Processor Interface ASIC) based cameras. This camera outputs an MJPEG 16stream at up to vga size. It implements the Video4Linux interface as much as 17possible. Since the V4L interface does not support compressed formats, only 18an mjpeg enabled application can be used with the camera. We have modified the 19gqcam application to view this stream. 20 21The driver is implemented as two kernel modules. The cpia2 module 22contains the camera functions and the V4L interface. The cpia2_usb module 23contains usb specific functions. The main reason for this was the size of the 24module was getting out of hand, so I separated them. It is not likely that 25there will be a parallel port version. 26 27Features 28-------- 29 30- Supports cameras with the Vision stv6410 (CIF) and stv6500 (VGA) cmos 31 sensors. I only have the vga sensor, so can't test the other. 32- Image formats: VGA, QVGA, CIF, QCIF, and a number of sizes in between. 33 VGA and QVGA are the native image sizes for the VGA camera. CIF is done 34 in the coprocessor by scaling QVGA. All other sizes are done by clipping. 35- Palette: YCrCb, compressed with MJPEG. 36- Some compression parameters are settable. 37- Sensor framerate is adjustable (up to 30 fps CIF, 15 fps VGA). 38- Adjust brightness, color, contrast while streaming. 39- Flicker control settable for 50 or 60 Hz mains frequency. 40 41Making and installing the stv672 driver modules 42----------------------------------------------- 43 44Requirements 45~~~~~~~~~~~~ 46 47Video4Linux must be either compiled into the kernel or 48available as a module. Video4Linux2 is automatically detected and made 49available at compile time. 50 51Setup 52~~~~~ 53 54Use ``modprobe cpia2`` to load and ``modprobe -r cpia2`` to unload. This 55may be done automatically by your distribution. 56 57Driver options 58~~~~~~~~~~~~~~ 59 60.. tabularcolumns:: |p{13ex}|L| 61 62 63============== ======================================================== 64Option Description 65============== ======================================================== 66video_nr video device to register (0=/dev/video0, etc) 67 range -1 to 64. default is -1 (first available) 68 If you have more than 1 camera, this MUST be -1. 69buffer_size Size for each frame buffer in bytes (default 68k) 70num_buffers Number of frame buffers (1-32, default 3) 71alternate USB Alternate (2-7, default 7) 72flicker_freq Frequency for flicker reduction(50 or 60, default 60) 73flicker_mode 0 to disable, or 1 to enable flicker reduction. 74 (default 0). This is only effective if the camera 75 uses a stv0672 coprocessor. 76============== ======================================================== 77 78Setting the options 79~~~~~~~~~~~~~~~~~~~ 80 81If you are using modules, edit /etc/modules.conf and add an options 82line like this:: 83 84 options cpia2 num_buffers=3 buffer_size=65535 85 86If the driver is compiled into the kernel, at boot time specify them 87like this:: 88 89 cpia2.num_buffers=3 cpia2.buffer_size=65535 90 91What buffer size should I use? 92~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 93 94The maximum image size depends on the alternate you choose, and the 95frame rate achieved by the camera. If the compression engine is able to 96keep up with the frame rate, the maximum image size is given by the table 97below. 98 99The compression engine starts out at maximum compression, and will 100increase image quality until it is close to the size in the table. As long 101as the compression engine can keep up with the frame rate, after a short time 102the images will all be about the size in the table, regardless of resolution. 103 104At low alternate settings, the compression engine may not be able to 105compress the image enough and will reduce the frame rate by producing larger 106images. 107 108The default of 68k should be good for most users. This will handle 109any alternate at frame rates down to 15fps. For lower frame rates, it may 110be necessary to increase the buffer size to avoid having frames dropped due 111to insufficient space. 112 113========== ========== ======== ===== 114Alternate bytes/ms 15fps 30fps 115========== ========== ======== ===== 116 2 128 8533 4267 117 3 384 25600 12800 118 4 640 42667 21333 119 5 768 51200 25600 120 6 896 59733 29867 121 7 1023 68200 34100 122========== ========== ======== ===== 123 124Table: Image size(bytes) 125 126 127How many buffers should I use? 128~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 129 130For normal streaming, 3 should give the best results. With only 2, 131it is possible for the camera to finish sending one image just after a 132program has started reading the other. If this happens, the driver must drop 133a frame. The exception to this is if you have a heavily loaded machine. In 134this case use 2 buffers. You are probably not reading at the full frame rate. 135If the camera can send multiple images before a read finishes, it could 136overwrite the third buffer before the read finishes, leading to a corrupt 137image. Single and double buffering have extra checks to avoid overwriting. 138 139Using the camera 140~~~~~~~~~~~~~~~~ 141 142We are providing a modified gqcam application to view the output. In 143order to avoid confusion, here it is called mview. There is also the qx5view 144program which can also control the lights on the qx5 microscope. MJPEG Tools 145(http://mjpeg.sourceforge.net) can also be used to record from the camera.