>> ARDUINO YÚN - SO MANY POSSIBILITIES
Small device, hidden power - this is one of my favourite Arduino devices so far.
As part of my research into
IoT security feasibility I got my hands on an
Arduino Yún, an official Arduino device that not only
comes with a 16Mhz Atmel ATmega32u4 CPU but an accompanying 400Mhz Atheros
AR9331 running a Linux variant known as
(based on OpenWRT). I was interested to know if this extra CPU could be
utilized for more intensive tasks that the low powered Atmel couldn't
handle - here is how I got it working.
The first step was to identify exactly how to execute tasks on the Linux
CPU and exchange information back and forth - the Arduino team have created
a mini library called
YunBridgeLibrary which effectively uses a proprietary protocol
sending commands and data back and forth over a secondary Serial interface
(HardwareSerial) on the Atmel CPU.
The examples show how to interact with standard Linux shell commands and
services - but what about running your own applications to do complex tasks?
For that we would need to compile C/C++ code into native MIPS binaries -
using a cross-compiler or, if we can find it, a pre-compiled gcc to use
directly on the device (much less work for sure!)
I came across
sniff.org.uk's post on how they figured
out how to build gcc directly for the Yún - and viola, they even provide
a pre-compiled version for anyone to use (160Mb download). Unfortunately,
the default file system on SD cards is FAT32 - which if you try to extract
the tarball to you will find quickly that it wont support symbolic links =
I used Paragon ExtFS for MacOSX to format my SD card
to the traditional "ext3" file system - extracted the tarball then inserted
it into the Yún; viola, it mounted without any complaints. Alternatively
you could also use the tutorial ExpandingYunDiskSpace to do
the same and then copy the tarball to the device and extract directly.
The default password for the Arduino Uún is "arduino" - it is
possible (and recommended to change it) but once you have extracted the
gcc tarball to where ever your compatible file system is (/mnt/sda1
or /mnt/sda2 - depending on which method you used), set up your
path and you should be able to compile your first C program directly on
the device itself. The SD card is only required for compilation - you can
simply move the compiled programs to the root directory once created
(or, put them in their own directory).
Now your native application is compiled - it is time to code an
arduino sketch and run it.
This will effectively execute the command /my_program 123 456
on the device and echo the results of the process on the Serial
connection (from the arduino IDE) - of course, you would customize
this to your own needs and put the data returned into a format you
could utilize and process. With the limited SRAM available on the
Atmel side of the device - you may want to consider writing files
to the /tmp directory if you need to pass large amounts
of data; it will be faster and much more memory efficient.
To give you an idea of performance, the Yún is almost exactly
the same as the UNO or Leonardo - it just has this extra CPU. In my
RSA 1024 speed comparisons, the difference was staggering - 12682ms
verses 707ms for the same C code; this includes the 200-300ms overhead
that the bridge library has as well.
So, what do you plan to do with your Arduino Yún now you know
how to use that extra CPU?