Raspberry Pi

My Raspberry Pi finally arrived after 4 months:

The stable Debian distribution “Squeeze” does not contain support for all of the Raspberry Pi features. That means there is no way around the the latest Debian “Wheezy” image:  http://www.raspberrypi.org/archives/1435

But even with the latest image version there is still some configuration effort left…

WLAN Stick

For network connectivity I have chosen the Conrad WLAN Stick N150 Nano, which is based on the following chipset: USB: 0BDA:8176 Realtek Semiconductor Corp. RTL8188CUS 802.11n WLAN Adapter.
Unfortunately this chipset has some issues with the current drivers from both Debian Linux images as discussed in the forum thread Automatic setup for RTL8188CUS based wifi adapters. By executing the script install-rtl8188cus-latest.sh from the forum thread, the adapter started working immediately after the script was finished.
The general WLAN configuration is described in detail in the Debian Wiki: http://wiki.debian.org/WiFi/HowToUse#Command_Line

Analog Audio

The following commands must be issued to activate the analog output of the Raspberry Pi:

sudo apt-get install alsa-utils gstreamer-tools madplay gstreamer0.10-alsa  
sudo modprobe snd_bcm2835  
sudo amixer cset numid=3 1 

Now you can play a mp3 audio stream via the ALSA device like this:

gst-launch souphttpsrc location=http://dradio_mp3_dlf_m.akacast.akamaistream.net/7/249/142684/v1/gnl.akacast.akamaistream.net/dradio_mp3_dlf_m \\  
   ! mad \\  
   ! audioconvert \\
   ! audioresample \\
   ! alsasink device=hw:0

The fact that the device needs to be specified explicitly “device=hw:0” indicates another issue here as this is not necessary on my desktop Linux machine.

For testing the output without an internet connection you can use the following commands:

cd /opt/vs/src/hello_pi  
make
./hello_audio

The audio output is not as clear as I expected it to be. I still hear some clicking noises when playing a stream. I hope this will be fixed in upcoming releases of the analog audio driver.

GPIO Ports

In a first test I connected a button to the GPIO port 0 and tried to read the switch state via a simple script:

sudo -s  
echo "0" > /sys/class/gpio/export  
echo "in" > /sys/class/gpio/gpio0/direction  
watch cat /sys/class/gpio/gpio0/value

When pressing and holding the button pressed for at least 2 seconds you will see that the value turns from 1 (not pressed) to 0 (pressed).

Because the polling approach consumes too much resources I started looking after an interrupt solution.
The Debian “Wheezy” Beta version does not support interrupts for input ports. However, patches exist and have been included into Linux kernel version 3.2.21 from here: http://www.bootc.net/archives/2012/07/01/new-revision-of-3-2-21/
In order to download the kernel and activate it, run the following commands (NOTE: the kernel version changes quite frequently, so the 3.2.23 might be outdated):

wget http://apt.bootc.net/debian/pool/main/l/linux-source-3.2.23-rpi1+/linux-image-3.2.23-rpi1+_1_armel.deb  
sudo dpkg -i linux-image-3.2.23-rpi1+_1_armel.deb
sudo cp /boot/vmlinuz-3.2.23-rpi1+ /boot/kernel.img

After a reboot the kernel provides interrupts on GPIO input ports and a simple C application published on the following thread demonstrates how to handle interrupts:  http://www.raspberrypi.org/phpBB3/viewtopic.php?t=7509&p=92074