Hello,

I should probably explain that I'm a linux and BBB novice, and am currently 
experiencing a crazily steep learning curve. So please bear with me while I 
ask what are probably incredibly rudimentary questions...

I'm interested in doing some realtime control (servos, reading encoders 
etc) on my BBB rev C under Xenomai, and after some reading around it seemed 
like the simplest way to get started was using the pre-built machinekit 
images found 
here: 
http://elinux.org/Beagleboard:BeagleBoneBlack_Debian#BBW.2FBBB_.28All_Revs.29_Machinekit

So, having installed this image I can now ssh into the BBB from a Xubuntu 
install running under VMware on my PC.

I thought a good place to start would be blinking an LED. To that end I've 
compiled the C++ program here 
<http://inspire.logicsupply.com/2014/07/beaglebone-c-programming-example.html>, 
which works (only) if I use sudo, i.e. sudo ./myprog. I've also tried 
turning them on and off at the command line as outlined on Derek Molloy's 
site 
<http://derekmolloy.ie/beaglebone-controlling-the-on-board-leds-using-c/>, 
but this doesn't work:

cd /sys/class/leds
cd beaglebone:green:usr0
echo none > trigger

-bash: trigger: Permission denied

sudo echo none > trigger doesn't work either...

What am I doing wrong?

Also more generally, is this approach of accessing LEDs and GPIOs through 
the file system the right way to go if I'm interested in doing things 
quickly? Intuitively it feels like it'd be slow - is there another way?

Incidentally this <https://hackaday.io/project/12827-double-pendulum-cart> 
is what I'm aiming to do eventually. 

Thanks for any help, it's appreciated!

Luke


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