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 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. You will already run into problems already, and it is much easier and faster to address them this way. 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:
# wget http://kernel.org/pub/linux/kernel/v2.6/linux-2.6.24.tar.bz2
- 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
- load the modules:
# insmod drivers/media/video/v4l1-compat.ko # insmod drivers/media/video/v4l2-common.ko # insmod drivers/media/video/videodev.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/linux-uvc # 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
Known problems
- the resolution was limited to 160x120 with our Philips SPC620NC