Installation
Making and installing the CPiA2 driver module.
Requirements
This should work with 2.4 (2.4.23 and later) and 2.6 kernels, but has only been tested on 2.6. Video4Linux must be either compiled into the kernel or available as a module. Video4Linux2 is automatically detected and made available at compile time.
Compiling
As root, do a make install. This will compile and install the modules into the media/video directory in the module tree. For 2.4 kernels, use Makefile_2.4 (aka do make -f Makefile_2.4 install).
Setup
Use 'modprobe cpia2' to load and 'modprobe -r cpia2' to unload. This may be done automatically by your distribution.
Driver options
Option Description ------ ----------- video_nr video device to register (0=/dev/video0, etc) range -1 to 64. default is -1 (first available) If you have more than 1 camera, this MUST be -1. buffer_size Size for each frame buffer in bytes (default 68k) num_buffers Number of frame buffers (1-32, default 3) alternate USB Alternate (2-7, default 7) flicker_freq Frequency for flicker reduction(50 or 60, default 60) flicker_mode 0 to disable, or 1 to enable flicker reduction. (default 0). This is only effective if the camera uses a stv0672 coprocessor.
Setting the options
If you are using modules, edit /etc/modules.conf and add an options line like this:
options cpia2 num_buffers=3 buffer_size=65535
If the driver is compiled into the kernel, at boot time specify them like this:
cpia2=num_buffers:3,buffer_size:65535
What buffer size should I use?
The maximum image size depends on the alternate you choose, and the frame rate achieved by the camera. If the compression engine is able to keep up with the frame rate, the maximum image size is given by the table below. The compression engine starts out at maximum compression, and will increase image quality until it is close to the size in the table. As long as the compression engine can keep up with the frame rate, after a short time the images will all be about the size in the table, regardless of resolution. At low alternate settings, the compression engine may not be able to compress the image enough and will reduce the frame rate by producing larger images. The default of 68k should be good for most users. This will handle any alternate at frame rates down to 15fps. For lower frame rates, it may be necessary to increase the buffer size to avoid having frames dropped due to insufficient space.
Image size(bytes)
Alternate bytes/ms 15fps 30fps
2 128 8533 4267
3 384 25600 12800
4 640 42667 21333
5 768 51200 25600
6 896 59733 29867
7 1023 68200 34100
How many buffers should I use?
For normal streaming, 3 should give the best results. With only 2, it is possible for the camera to finish sending one image just after a program has started reading the other. If this happens, the driver must drop a frame. The exception to this is if you have a heavily loaded machine. In this case use 2 buffers. You are probably not reading at the full frame rate. If the camera can send multiple images before a read finishes, it could overwrite the third buffer before the read finishes, leading to a corrupt image. Single and double buffering have extra checks to avoid overwriting.