Webcam
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It is possible to plug and use a webcam on the Freerunner. This is a very rough list of the steps required to do so with Debian Lenny installed.
The webcam used to perform this example is a Philips SPC620NC, using the [UVC] driver.
The method described here is still rather ugly, feel free to improve it.
Contents |
Make it work on a PC
To be safe, you just first ensure the webcam works on a regular PC, and Linux in particular. This will minimise the problems you are likely to face (though it may not eliminate them altogether). The regular documentation applies:
Add video support to the kernel
The 2.6.24 kernel is provided without video input support enabled. There is a way to add the necessary modules without recompiling everything:
- download the source code for the kernel:
- make sure you have bzip2 and development tools installed:
- apt-get install bzip2 gcc make libc6-dev libncurses5-dev
- uncompress it in /usr/src:
- cd /usr/src
- tar -xjvf $OLDPWD/linux-2.6.24.tar.bz2
- fix links bluntly in /lib/modules:
- ln -sf /usr/src/linux-2.6.24 /lib/modules/2.6.24/build
- initialize the kernel sources with the current configuration:
- cd /usr/src/linux-2.6.24
- gzip -dc /proc/config.gz > .config
- make oldconfig # just say "n" to power management debugging support
- add video support:
- make menuconfig
Basically, look for "Device drivers", "Multimedia devices", then enable "Video For Linux", "Video For Linux API 1", "Video For Linux API 1 compatible Layer", "Video capture adapters" as modules. If the driver for your webcam is found in the kernel already, also enable it there.
- compile the relevant kernel modules:
- make drivers/media/video/v4l1-compat.ko
- make drivers/media/video/v4l2-common.ko
- make drivers/media/video/videodev.ko
- make drivers/media/video/compat_ioctl32.ko
- load the modules:
- insmod drivers/media/video/v4l1-compat.ko
- insmod drivers/media/video/v4l2-common.ko
- insmod drivers/media/video/videodev.ko
- insmod drivers/media/video/compat_ioctl32.ko
The errors encountered while loading modules can be obtained with the "dmesg" command. They are typically also logged in /var/log/messages.
Compile the UVC driver
To obtain and compile the latest source tree for the driver:
- apt-get install subversion
- svn checkout svn://svn.berlios.de/linux-uvc/linux-uvc/trunk
- cd trunk
- make
And if all goes well:
- insmod uvcvideo.ko
Add the device node
In our case, the relevant device node was not created automatically. Here's how to do so:
- mkdir -p /dev/v4l
- mknod /dev/v4l/video0 c 81 0
Plug the camera itself
The Freerunner needs to run in USB host mode in order to do this. A special USB cable (or gender changer) is necessary to do so.
Again, you can use the command "dmesg" to verify that the camera is properly recognized.
Install and try a viewer
A good webcam test application is luvcview. You can install and test it this way:
- apt-get install luvcview
- luvcview -f yuv -d /dev/v4l/video0
Webcam in action: [1]
Known problems
- the resolution was limited to 160x120 with our Philips SPC620NC
This limitation may depend on video format; for example, luvcvideo on FreeRunner&debian told me that Logitech QuickCam E3500+ supports up to 176x144 with YUV, and up to 640x480 with MJPG