EBC Exercise 23 Configuring the Kernel

There are several ways to get and configure the kernel. You could go to the The Linux Kernel Archives, find the ---arm--- branch, download a kernel and patch it for the omap. You could use git to get a kernel. Or you could just use bitbake like we did before.

Let's first learn how to do it the bitbake way.

bitbake
When you did ECE597 Installing The Ångström Distribution you used bitbake to build console-image. During that build the kernel was downloaded and compiled. If you used the default configure, the source code was removed once it was done. Check and see: cd ${OETREE}/angstrom-dev/work/beagleboard-angstrom-linux-gnueabi ls You should see a directory starting with. The rest of the name tells what version you have. Change to that directory and see what's there: cd linux-omap-2.6.29-r46 ls If you see a git directory, you are in luck. If you see just a temp directory you need to do the following to reload the sources: cd ${OETREE}/build/conf gedit local.conf Find the line near the top that says  and comment it out. Save the file and then: cd ${OETREE}/openembedded $ bitbake -c clean linux-omap-2.6.29 $ bitbake -f -c compile linux-omap-2.6.29 ''Note: These instructions are based on this which is a good reference on finding and modifying the kernel in the oe distribution. In fact, wh1t3s seems to have several nice tips.''
 * 1) INHERIT += " rm_work "


 * The first bitbake command tells bitbake to remove the previously made binary file for that package (think "make clean"), which will force it to re-do what it previously did with the console-image build.


 * The second bitbake line forces bitbake to rebuild the linux-omap package, which will require re-extracting the previously deleted source code, and apply the relevant OE related patches.

This took some three hours on my machine. Your mileage may vary. Once done go back to cd ${OETREE}/angstrom-dev/work/beagleboard-angstrom-linux-gnueabi/linux-omap-2.6.29-r46 ls You should now see the git directory. cd to it and look around.

You can now configure the kernel. sudo apt-get install libqt3-mt-dev make xconfig After saving the configuration changes to update the .config file, it is a simple matter of rerunning the forced compile step from above to rebuild the kernel: $ bitbake -f -c compile linux-omap-2.6.29 $ bitbake -f -c deploy linux-omap-2.6.29 If your kernel configuration modifications happen to result in the generation of any loadable modules, then you will wind up with another file in the deployment images folder:


 * What does the bitbake deploy command do? See if you can find out

$ cd ${OETREE}/angstrom-dev/deploy/glibc/images/beagleboard $ ls

Doing it yourself
If you would prefer to maintain your own kernel source tree outside of OE, see these directions: BeagleBoardLinuxKernel

Alternatively it is possible to run the official omap branch of the linux kernel. Take a peek at this page. BeagleBoard (Please continue reading for the modifications I needed)

PATH=~/oe/angstrom-dev/cross/armv7a/bin:~/oe/angstrom-dev/staging/i686-linux/usr/bin:$PATH # add cross tools to your path make ARCH=arm CROSS_COMPILE=arm-angstrom-linux-gnueabi- distclean make ARCH=arm CROSS_COMPILE=arm-angstrom-linux-gnueabi- omap3_beagle_defconfig make ARCH=arm CROSS_COMPILE=arm-angstrom-linux-gnueabi- menuconfig # only needed if you want to change the default configuration make ARCH=arm CROSS_COMPILE=arm-angstrom-linux-gnueabi- uImage
 * Since we are using OE, our paths are set up slightly different, I have made the relevant changes below that I needed to do it manually. Take note on the second path command is arch specific (if you get an error about mkimage not being found, make sure you have the second path right)


 * It is important to note that the kernel in the official branch will be newer then the ones that OE provides (2.6.33 at the time of this writing), and as such there are no OE related patches to apply.


 * There is no reason why you can't steal the OE kernel config, and apply it to the newer kernel. See if you can figure out how to do this.  (Hint: You will need to combine both above links directions)


 * Alternatively if you've previously built the kernel, take a peek in your ${OETREE}/downloads. This is where the old kernel source (pre-patches) was downloaded, and see if you can manually apply the OE patches.