Dual Relay Shield v2 (green thing on top) connected to a Rascal 0.6 (red and yellow thing on bottom). The DRS lets you switch 2 relays on and off to control devices up to 5 amps at 220 volts.

The shield has two relays that can switch up to 5 amps — this could be a pair of lights, motors, speakers, etc. It also has an integrated I2C temperature sensor. You could use this to build, for instance, a web-based thermostat. I expect Brandon will set up a Rascal demo or tutorial using the shield in the near future, to which I’ll link from here once it exists.

All of the design files are open source. You can find them on my Rascal Shield github.

0. I had to first install some packages for the build to succeed:

sudo apt-get install libxml2 libxml2-dev python-dev

1. Download the current tarball listed under http://projects.unbit.it/uwsgi/wiki/WikiStart#Getit

2. Untar and then follow the instructions from projects.unbit.it/uwsgi/wiki/Install

tar xzvf uwsgi-1.0.2.1.tar.gz
cd uwsgi-1.0.2.1
make

3. The compile should complete successfully with the last line reading like this:

*** uWSGI is ready, launch it with ./uwsgi ***

4. Start it like this:

./uwsgi --http :80

In future posts, I’ll look at modifying the uWSGI source code to support Python-programmed user mode interrupt handlers.

As an example, let’s download Dave Hylands’s gpio-event driver and usermode application for the Gumstix Overo.  As it turns out, we can compile this driver for the Rascal unmodified once we get the paths right.  Check out the Rascal kernel git branch to ~/rascal/linux-2.6 and download Hylands’s code to ~/rascal/gpio-event.  Modify ~/rascal/gpio-event/module/Makefile to use these alternate variable definitions:

CROSS_COMPILE ?= /opt/eldk/usr/arm-linux-gnueabi
KERNEL_PATH   ?= /home/mike/rascal/linux-2.6/arch/arm/kernel
ARCH          ?= arm

(Of course, the /home/mike prefix is specific to my machine.  What matters is that $(KERNAL_PATH) contains a bunch of C source files like module.c.)

Then do this:

cd ~/rascal/gpio-event/module
make -C ~/rascal/linux-2.6/ M=`pwd` ARCH=arm modules

You should get a file called gpio-event-drv.ko in ~/rascal/gpio-event/module.  SCP this file to the Rascal and ssh in to it.  From the directory where you put the gpio-event-drv.ko file, you can use these commands:

insmod gpio-event-drv.ko
rmmod gpio-event-drv.ko

to load and unload the module respectively.