Category Archives: Raspberry Pi

General tips about using the Raspberry Pi and Raspberry Wheezy (the operating system).

Building a loadable kernel module

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I needed to design, implement and build a loadable kernel module in order to access the ARM11 performance counters from user-space. I will slowly roll out the design and code for the kernel module. But, first, I’ve posted my notes for building a loadable kernel module. It’s easier to explain the process of building the module and the internal design of the module if I separate the two discussions.

There were a few problems along the way. The kernel source for Raspbian Wheezy 3.6.11+ is not available using Synaptic. Only 3.6.9 is available through Synaptic. I needed to download the source for 3.6.11+ from github.com in order to match the installed Linux image. Next, I needed the module version information for 3.6.11+. Usually this information is built along with the kernel and is stored in the file named Module.symvers. Raspbian Wheezy takes 10+ hours to build on the Raspberry Pi, according to reports on the Web, so I didn’t want to undertake a long-running kernel build just to generate the version information. Fortunately, I could download Module.symvers from github.com, too.

I hope the next Raspbian Wheezy distro has all of the essentials for a module build — headers, version information, the whole she-bang. This would really help a brother out because many people are building custom hardware for the RPi and they need to build custom device drivers, too.

I’m currently in the process of writing pages on performance monitoring on the RPi. That discussion will include the design and code for my kernel module. The kernel module is about as simple as can be and is a kind of “Hello world” example. Please stay tuned.

Raspberry Pi tips and tricks

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If you’re new to the world of Raspberry Pi, you should check out the page about Raspberry Pi tips and tricks. The page has all of the things that I did to configure Raspberry Pi and get started with the operating system, Raspbian Wheezy.

One of the most important things you should do is to configure the operating system for your geographic location or “locale”. The Raspbian Wheezy image is configured for the United Kingdom (UK). Therefore, the operating system and other software formats the data, time, and money for the UK. If you’re living somewhere else, you’ll want to set things to local convention. That’s where the locale comes into play.

Run the raspi-config program to change settings:

sudo raspi-config

The program implements a simple quasi-GUI where you navigate using the arrow keys. The space bar makes selections and the enter key confirms selections, etc.

Of course, you should set the timezone using the change_timezone option. Use the change_locale option to set your locale.

You would think that change_locale would set the keymap for your keyboard, but no! You need to change the keymap (keyboard layout) using the configure_keyboard option. If you type a key like “|” and you get a different character, you probably need to change the keymap to match your keyboard. Raspian Wheezy will build the new keymap when it reboots the next time (a step that takes a little time to execute).

Finally, you should know how to properly shut down the operating system and Raspberry Pi. I use the shutdown program:

sudo shutdown -h now

The -h option tells the processor to halt after shutdown, allowing you to safely pull the adapter plug from the wall. Use the -r option if you want to reboot instead. Don’t forget to do this since the OS may need to update information in permanent storage, thereby avoiding file system corruption.

Hey, don’t forget to have fun with your new system!