Archive for January, 2012

Rascal/Arduino Dual Relay Shield v2

January 25, 2012 at 2:23 pm · Filed under dual relay shield

Yesterday, I assembled a few copies of my Dual Relay Shield (rev 2). Here’s a picture of its handsome exterior:

Dual Relay Shield v2

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.

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Building uWSGI on Ubuntu 11.xx

January 25, 2012 at 1:26 pm · Filed under uWSGI

uWSGI is the HTTP server included with the Rascal. I want to fiddle with its source code and extend it, so I started by building the stock distribution on an x86 Ubuntu 11.04 box. This is how I did it.

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.

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Compiling and loading kernel modules on the Rascal

January 22, 2012 at 3:15 pm · Filed under low-level rascaling, notes to self

Here’s a tut showing how to cross-compile your own device driver (as a kernel module) on the Rascal and then load/unload it into Linux on the device.  I’ll assume you have previously followed these instructions to create a kernel build environment on your development PC.

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.

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How to beat the Wikipedia SOPA blackout

January 18, 2012 at 12:13 am · Filed under wikipedia

I was able to download a local copy of Wikipedia and a reader and set them up in less than 5 minutes.  Used this tut:  http://lifehacker.com/5876833

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